A marine coastal ecosystem is a
marine ecosystem
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the sur ...
which occurs where the land meets the ocean. Marine coastal ecosystems include many different types of
marine habitat
Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...
s, such as
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
and
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...
s,
salt marsh
A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is domin ...
es and
mangrove forests,
seagrass meadow
A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...
s and
coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
s,
kelp forest
Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Ea ...
s and backwaters. Directly and indirectly these provide a vast range of
ecosystem service
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. ...
s for humans, such as sequestering carbon, cycling nutrients and elements, providing nurseries and fishing grounds for commercial fisheries, preventing coastal erosion and moderating extreme events, as well as providing recreational services and supporting tourism.
Overview
![Continental shelf](https://upload.wikimedia.org/wikipedia/commons/3/32/Continental_shelf.png)
Coastal seas are highly productive systems, providing an array of ecosystem services to humankind, such as processing of nutrient effluents from land and climate regulation.
However, coastal ecosystems are threatened by human-induced pressures such as climate change and
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
. In the coastal zone, the fluxes and transformations of nutrients and carbon sustaining coastal ecosystem functions and services are strongly regulated by
benthic (that is, occurring at the
seafloor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...
) biological and chemical processes.
Coastal systems also contribute to the regulation of climate and
nutrient cycle
A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cyc ...
s, by efficiently processing anthropogenic emissions from land before they reach the ocean. The high value of these ecosystem services is obvious considering that a large proportion of the world population lives close to the coast.
Currently, coastal seas around the world are undergoing major ecological changes driven by human-induced pressures, such as climate change, anthropogenic nutrient inputs,
overfishing and the spread of
invasive species.
In many cases, the changes alter underlying ecological functions to such an extent that new states are achieved and
baselines are shifted.
In 2015, the United Nations established 17
Sustainable Development Goals with the aim of achieving certain targets by 2030. Their mission statement for their 14th goal, ''
Life below water
Sustainable Development Goal 14 (Goal 14 or SDG 14) is about "Life below water" and is one of the 17 Sustainable Development Goals established by the United Nations in 2015. The official wording is to "Conserve and sustainably use the oceans, seas ...
'', is to "conserve and sustainably use the oceans, seas and marine resources for sustainable development".
[United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development]
A/RES/71/313
The United Nations has also declared 2021–2030 the
UN Decade on Ecosystem Restoration
The United Nations Decade on Ecosystem Restoration runs from 2021 to 2030. Similar to other nature related international decades, its purpose is to promote the United Nation's environmental goals. Specifically, to facilitate global cooperation for ...
, but restoration of coastal ecosystems is not receiving appropriate attention.
Coastal habitats
Intertidal zone
Intertidal zones are the areas that are visible and exposed to air during low tide and covered up by saltwater during high tide.
There are four physical divisions of the intertidal zone with each one having its distinct characteristics and wildlife. These divisions are the Spray zone, High intertidal zone, Middle Intertidal zone, and Low intertidal zone. The Spray zone is a damp area that is usually only reached by the ocean and submerged only under high tides or storms. The high intertidal zone is submerged at high tide but remains dry for long periods between high tides.
Due to the large variance of conditions possible in this region, it is inhabited by resilient wildlife that can withstand these changes such as barnacles, marine snails, mussels and hermit crabs.
Tides flow over the middle intertidal zone two times a day and this zone has a larger variety of wildlife.
The low intertidal zone is submerged nearly all the time except during the lowest tides and life is more abundant here due to the protection that the water gives.
Estuaries
Estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
occur where there is a noticeable change in salinity between saltwater and freshwater sources. This is typically found where rivers meet the ocean or sea. The wildlife found within estuaries is unique as the water in these areas is brackish - a mix of freshwater flowing to the ocean and salty seawater.
Other types of estuaries also exist and have similar characteristics as traditional brackish estuaries. The Great Lakes are a prime example. There, river water mixes with lake water and creates freshwater estuaries.
Estuaries are extremely productive ecosystems that many humans and animal species rely on for various activities.
This can be seen as, of the 32 largest cities in the world, 22 are located on estuaries as they provide many environmental and economic benefits such as crucial habitat for many species, and being economic hubs for many coastal communities.
Estuaries also provide essential ecosystem services such as water filtration, habitat protection, erosion control, gas regulation nutrient cycling, and it even gives education, recreation and tourism opportunities to people.
Lagoons
Lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...
s are areas that are separated from larger water by natural barriers such as coral reefs or sandbars. There are two types of lagoons, coastal and oceanic/atoll lagoons. A coastal lagoon is, as the definition above, simply a body of water that is separated from the ocean by a barrier. An atoll lagoon is a circular coral reef or several coral islands that surround a lagoon. Atoll lagoons are often much deeper than coastal lagoons.
Most lagoons are very shallow meaning that they are greatly affected by changed in precipitation, evaporation and wind. This means that salinity and temperature are widely varied in lagoons and that they can have water that ranges from fresh to hypersaline.
Lagoons can be found in on coasts all over the world, on every continent except Antarctica and is an extremely diverse habitat being home to a wide array of species including birds, fish, crabs, plankton and more.
Lagoons are also important to the economy as they provide a wide array of ecosystem services in addition to being the home of so many different species. Some of these services include fisheries, nutrient cycling, flood protection, water filtration, and even human tradition.
Reefs
Coral reefs
Coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
s are one of the most well-known marine ecosystems in the world, with the largest being the
Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
. These reefs are composed of large coral colonies of a variety of species living together. The corals from multiple symbiotic relationships with the organisms around them. Coral reefs are being heavily affected by global warming. They are one of the most vulnerable marine ecosystems. Due to marine heatwaves that have high warming levels coral reefs are at risk of a great decline, loss of its important structures, and exposure to higher frequency of marine heatwaves.
File:The Coral Reef at the Andaman Islands.jpg,
File:Global distribution of coral, mangrove, and seagrass diversity.png, center,
File:Dugong Marsa Alam.jpg,
Bivalve reefs
![Ecosystem services delivered by epibenthic bivalve reefs](https://upload.wikimedia.org/wikipedia/commons/1/18/Ecosystem_services_delivered_by_epibenthic_bivalve_reefs.png)
Bivalve reefs provide coastal protection through erosion control and shoreline stabilization, and modify the physical landscape by
ecosystem engineering
An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem enginee ...
, thereby providing habitat for species by facilitative interactions with other habitats such as
tidal flat
Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
benthic communities,
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
es and
marsh
A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...
es.
[Ysebaert T., Walles B., Haner J., Hancock B. (2019) "Habitat Modification and Coastal Protection by Ecosystem-Engineering Reef-Building Bivalves". In: Smaal A., Ferreira J., Grant J., Petersen J., Strand Ø. (eds) ''Goods and Services of Marine Bivalves''. Springer. ]
Vegetated
Vegetated coastal ecosystems occur throughout the world, as illustrated in the diagram on the right.
Seagrass beds are found from cold polar waters to the tropics.
Mangrove forests are confined to tropical and sub-tropical areas, while
tidal marsh
A tidal marsh (also known as a type of "tidal wetland") is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes are commonly zoned into lower marshes ( ...
es are found in all regions, but most commonly in temperate areas. Combined, these ecosystems cover about 50 million hectares and provide a diverse array of
ecosystem service
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. ...
s such as fishery production, coastline protection, pollution buffering, as well as high rates of
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...
.
Rapid loss of vegetated coastal ecosystems through land-use change has occurred for centuries, and has accelerated in recent decades. Causes of habitat conversion vary globally and include conversion to aquaculture, agriculture, forest over-exploitation, industrial use, upstream dams, dredging, eutrophication of overlying waters, urban development, and conversion to open water due to accelerated sea-level rise and subsidence.
Vegetated coastal ecosystems typically reside over organic-rich sediments that may be several meters deep and effectively lock up carbon due to low-oxygen conditions and other factors that inhibit decomposition at depth.
These carbon stocks can exceed those of terrestrial ecosystems, including forests, by several times. When coastal habitats are degraded or converted to other land uses, the sediment carbon is destabilised or exposed to oxygen, and subsequent increased microbial activity releases large amounts of greenhouse gasses to the atmosphere or
water column
A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...
.
The potential economic impacts that come from releasing stored coastal
blue carbon to the atmosphere are felt worldwide. Economic impacts of greenhouse gas emissions in general stem from associated increases in droughts, sea level, and frequency of extreme weather events.
Coastal wetlands
![Map Halophytes](https://upload.wikimedia.org/wikipedia/commons/c/c2/Map_Halophytes.png)
Coastal wetlands are among the most productive ecosystems on Earth and generate vital services that benefit human societies around the world. Sediment-stabilization by wetlands such as salt marshes and mangroves serves to protect coastal communities from storm-waves, flooding, and land erosion. Coastal wetlands also reduce pollution from human waste, remove excess nutrients from the water column, trap pollutants, and sequester carbon. Further, near-shore wetlands act as both essential nursery habitats and feeding grounds for
game fish
Game fish, sport fish or quarry refer to popular fish pursued by recreational anglers, and can be freshwater or saltwater fish. Game fish can be eaten after being caught, or released after capture. Some game fish are also targeted commercial ...
, supporting a diverse group of economically important species.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
=Mangrove forests
=
Mangrove
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...
s are trees or shrubs that grow in low-oxygen soil near coastlines in tropical or subtropical latitudes.
They are an extremely productive and complex ecosystem that connects the land and sea. Mangroves consist of species that are not necessarily related to each other and are often grouped for the characteristics they share rather than genetic similarity.
Because of their proximity to the coast, they have all developed adaptions such as salt excretion and root aeration to live in salty, oxygen-depleted water.
Mangroves can often be recognized by their dense tangle of roots that act to protect the coast by reducing erosion from storm surges, currents, wave, and tides.
The mangrove ecosystem is also an important source of food for many species as well as excellent at
sequestering carbon
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...
dioxide from the atmosphere with global mangrove carbon storage is estimated at 34 million metric tons per year.
=Salt marshes
=
Salt marshes are a transition from the ocean to the land, where fresh and saltwater mix.
The soil in these marshes is often made up of mud and a layer of organic material called peat. Peat is characterized as waterlogged and root-filled decomposing plant matter that often causes low oxygen levels (hypoxia). These hypoxic conditions causes growth of the bacteria that also gives salt marshes the sulfurous smell they are often known for.
Salt marshes exist around the world and are needed for healthy ecosystems and a healthy economy. They are extremely productive ecosystems and they provide essential services for more than 75 percent of fishery species and protect shorelines from erosion and flooding.
Salt marshes can be generally divided into the high marsh, low marsh, and the upland border. The low marsh is closer to the ocean, with it being flooded at nearly every tide except low tide.
The high marsh is located between the low marsh and the upland border and it usually only flooded when higher than usual tides are present.
The upland border is the freshwater edge of the marsh and is usually located at elevations slightly higher than the high marsh. This region is usually only flooded under extreme weather conditions and experiences much less waterlogged conditions and salt stress than other areas of the marsh.
Seagrass meadows
Seagrasses form dense underwater
meadow
A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non- woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or arti ...
s which are among the most productive ecosystems in the world. They provide habitats and food for a diversity of marine life comparable to coral reefs. This includes invertebrates like shrimp and crabs, cod and flatfish, marine mammals and birds. They provide refuges for endangered species such as seahorses, turtles, and dugongs. They function as nursery habitats for shrimps, scallops and many commercial fish species. Seagrass meadows provide coastal storm protection by the way their leaves absorb energy from waves as they hit the coast. They keep
coastal waters
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
healthy by absorbing bacteria and nutrients, and slow the speed of climate change by sequestering carbon dioxide into the sediment of the ocean floor.
Seagrasses evolved from marine algae which colonized land and became land plants, and then returned to the ocean about 100 million years ago. However, today seagrass meadows are being damaged by human activities such as pollution from land runoff, fishing boats that drag dredges or trawls across the meadows uprooting the grass, and overfishing which unbalances the ecosystem. Seagrass meadows are currently being destroyed at a rate of about two football fields every hour.
File:Fan mussel (Pinna nobilis).jpg, Seagrass meadow
File:Diver in kelp forest.jpg, Kelp forest
Kelp forests
Kelp forests occur worldwide throughout
temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
and
polar coastal oceans.
[Mann, K.H. 1973. Seaweeds: their productivity and strategy for growth. Science 182: 975-981.] In 2007, kelp forests were also discovered in
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
waters near
Ecuador
Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ' ...
.
[Graham, M.H., B.P. Kinlan, L.D. Druehl, L.E. Garske, and S. Banks. 2007. Deep-water kelp refugia as potential hotspots of tropical marine diversity and productivity. Proceedings of the National Academy of Sciences 104: 16576-16580.]
Physically formed by brown
macroalgae
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
, kelp forests provide a unique habitat for marine organisms and are a source for understanding many ecological processes. Over the last century, they have been the focus of extensive research, particularly in
trophic
Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to:
* Trophic cascade
* Trophic coherence
* Trophic egg
* Trophic function
* Trophic hormone
* Trophic level index
* Trophic level
...
ecology, and continue to provoke important ideas that are relevant beyond this unique ecosystem. For example, kelp forests can influence coastal
oceanographic
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
patterns and provide many
ecosystem services
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. ...
.
[Steneck, R.S., M.H. Graham, B.J. Bourque, D. Corbett, J.M. Erlandson, J.A. Estes and M.J. Tegner. 2002. Kelp forest ecosystems: biodiversity, stability, resilience and future. Environmental Conservation 29: 436-459.]
However, the influence of humans has often contributed to kelp
forest degradation
Forest degradation is a process in which the biological wealth of a forest area is permanently diminished by some factor or by a combination of factors. "This does not involve a reduction of the forest area, but rather a quality decrease in its c ...
. Of particular concern are the effects of
overfishing nearshore ecosystems, which can release
herbivores from their normal population regulation and result in the
overgrazing
Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...
of kelp and other algae.
[Sala, E., C.F. Bourdouresque and M. Harmelin-Vivien. 1998. Fishing, trophic cascades, and the structure of algal assemblages: evaluation of an old but untested paradigm. Oikos 82: 425-439.] This can rapidly result in transitions to
barren landscapes where relatively few species persist.
[Dayton, P.K. 1985a. Ecology of kelp communities. Annual Review of Ecology and Systematics 16: 215-245.] Already due to the combined effects of
overfishing and
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, kelp forests have all but disappeared in many especially vulnerable places, such as
Tasmania
)
, nickname =
, image_map = Tasmania in Australia.svg
, map_caption = Location of Tasmania in AustraliaCoordinates:
, subdivision_type = Country
, subdi ...
's east coast and the coast of
Northern California
Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state of California. Spanning the state's northernmost 48 counties, its main population centers incl ...
. The implementation of
marine protected areas
Marine protected areas (MPA) are protected areas of seas, oceans, estuaries or in the US, the Great Lakes. These marine areas can come in many forms ranging from wildlife refuges to research facilities. MPAs restrict human activity for a conserv ...
is one management strategy useful for addressing such issues, since it may limit the impacts of fishing and buffer the ecosystem from additive effects of other environmental stressors.
Coastal ecology
Coastal food webs
Coastal waters include the waters in
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
and over
continental shelves
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
. They occupy about 8 percent of the total ocean area and account for about half of all the ocean productivity. The key nutrients determining
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
are nitrogen in coastal waters and phosphorus in lakes. Both are found in high concentrations in
guano
Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...
(seabird feces), which acts as a fertilizer for the surrounding ocean or an adjacent lake.
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown of ...
is the dominant nitrogen compound, and during its mineralization different nitrogen forms are produced.
Ecosystems, even those with seemingly distinct borders, rarely function independently of other adjacent systems. Ecologists are increasingly recognizing the important effects that cross-ecosystem transport of energy and nutrients have on plant and animal populations and communities. A well known example of this is how seabirds concentrate marine-derived nutrients on breeding islands in the form of feces (guano) which contains ~15–20% nitrogen (N), as well as 10% phosphorus.
These nutrients dramatically alter terrestrial ecosystem functioning and dynamics and can support increased primary and secondary productivity.
However, although many studies have demonstrated nitrogen enrichment of terrestrial components due to guano deposition across various taxonomic groups,
only a few have studied its retroaction on marine ecosystems and most of these studies were restricted to temperate regions and high nutrient waters.
In the tropics, coral reefs can be found adjacent to islands with large populations of breeding seabirds, and could be potentially affected by local nutrient enrichment due to the transport of seabird-derived nutrients in surrounding waters. Studies on the influence of guano on tropical marine ecosystems suggest nitrogen from guano enriches seawater and reef primary producers.
Reef building corals have essential nitrogen needs and, thriving in nutrient-poor tropical waters where nitrogen is a major limiting nutrient for primary productivity, they have developed specific adaptations for conserving this element. Their establishment and maintenance are partly due to their symbiosis with unicellular dinoflagellates, Symbiodinium spp. (zooxanthellae), that can take up and retain dissolved inorganic nitrogen (ammonium and nitrate) from the surrounding waters.
These zooxanthellae can also recycle the animal wastes and subsequently transfer them back to the coral host as amino acids, ammonium or urea. Corals are also able to ingest nitrogen-rich sediment particles and plankton. Coastal eutrophication and excess nutrient supply can have strong impacts on corals, leading to a decrease in skeletal growth,
Coastal predators
Food web
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one ...
theory predicts that current global declines in marine predators could generate unwanted consequences for many marine ecosystems. In coastal plant communities, such as kelp, seagrass meadows, mangrove forests and salt marshes, several studies have documented the far-reaching effects of changing predator populations. Across coastal ecosystems, the loss of marine predators appears to negatively affect coastal plant communities and the ecosystem services they provide.
The green world hypothesis predicts loss of predator control on
herbivores could result in runaway consumption that would eventually denude a landscape or seascape of vegetation. Since the inception of the green world hypothesis, ecologists have tried to understand the prevalence of indirect and alternating effects of predators on lower trophic levels (
trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...
s), and their overall impact on ecosystems.
Multiple lines of evidence now suggest that top predators are key to the persistence of some ecosystems.
With an estimated habitat loss greater than 50 percent, coastal plant communities are among the world’s most endangered ecosystems. As bleak as this number is, the predators that patrol coastal systems have fared far worse. Several predatory taxa including species of
marine mammal
Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their reli ...
s,
elasmobranch
Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gil ...
s, and
seabird
Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...
s have declined by 90 to 100 percent compared to historical populations.
Predator declines pre-date habitat declines,
suggesting alterations to predator populations may be a major driver of change for coastal systems.
There is little doubt that collapsing marine predator populations results from
overharvesting
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term app ...
by humans. Localized declines and extinctions of coastal predators by humans began over 40,000 years ago with subsistence harvesting.
However, for most large bodied, marine predators (
toothed whale
The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
s, large
pelagic fish
Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that do live on or near the bottom, and reef fish that are associated with coral reef ...
, sea birds,
pinniped
Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walru ...
s, and
otter
Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes wea ...
s) the beginning of their sharp global declines occurred over the last century, coinciding with the expansion of coastal human populations and advances in
industrial fishing
The fishing industry includes any industry or activity concerned with taking, culturing, processing, preserving, storing, transporting, marketing or selling fish or fish products. It is defined by the Food and Agriculture Organization as including ...
.
Following global declines in marine predators, evidence of trophic cascades in coastal ecosystems started to emerge, with the disturbing realisation that they affected more than just populations of lower trophic levels.
Understanding the importance of predators in coastal plant communities has been bolstered by their documented ability to influence ecosystem services. Multiple examples have shown that changes to the strength or direction of predator effects on lower trophic levels can influence
coastal erosion
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...
,
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...
,
and
ecosystem resilience. The idea that the
extirpation
Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...
of predators can have far-reaching effects on the persistence of coastal plants and their ecosystem services has become a major motivation for their conservation in coastal systems.
Seascape ecology
![Connectivity among different patch types in a tropical seascape](https://upload.wikimedia.org/wikipedia/commons/6/65/Connectivity_among_different_patch_types_in_a_tropical_seascape.png)
*
Connectivity
Connectivity may refer to:
Computing and technology
* Connectivity (media), the ability of the social media to accumulate economic capital from the users connections and activities
* Internet connectivity, the means by which individual terminal ...
Seascape ecology
Seascape ecology is a scientific discipline that deals with the causes and ecological consequences of spatial pattern in the marine environment, drawing heavily on conceptual and analytical frameworks developed in terrestrial landscape ecology.
...
is the marine and coastal version of
landscape ecology
Landscape ecology is the science of studying and improving relationships between ecological processes in the environment and particular ecosystems. This is done within a variety of landscape scales, development spatial patterns, and organizati ...
. It is currently emerging as an interdisciplinary and spatially explicit ecological science with relevance to marine management, biodiversity conservation, and restoration.
Seascapes are complex ocean spaces, shaped by dynamic and interconnected patterns and processes operating across a range of spatial and temporal scales.
Rapid advances in geospatial technologies and the proliferation of sensors, both above and below the ocean surface, have revealed intricate and scientifically intriguing ecological patterns and processes,
some of which are the result of human activities. Despite progress in the collecting, mapping, and sharing of ocean data, the gap between technological advances and the ability to generate ecological insights for marine management and conservation practice remains substantial.
For instance, fundamental gaps exist in the understanding of multidimensional spatial structure in the sea,
and the implications for planetary health and human wellbeing.
Deeper understanding of the multi-scale linkages between ecological structure, function, and change will better support the design of whole-system strategies for biodiversity preservation and reduce uncertainty around the consequences of human activity. For example, in the design and evaluation of marine protected areas (MPAs) and habitat restoration, it is important to understand the influence of spatial context, configuration, and connectivity, and to consider effects of scale.
Interactions between ecosystems
The diagram on the right shows the principal interactions between mangroves, seagrass, and coral reefs.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Coral reefs, seagrasses, and mangroves buffer habitats further inland from storms and wave damage as well as participate in a tri-system exchange of mobile fish and invertebrates. Mangroves and seagrasses are critical in regulating sediment, freshwater, and nutrient flows to coral reefs.
The diagram immediately below shows locations where mangroves, coral reefs, and seagrass beds exist within one km of each other. Buffered intersection between the three systems provides relative co-occurrence rates on a global scale. Regions where systems strongly intersect include Central America (Belize), the Caribbean, the Red Sea, the Coral Triangle (particularly Malaysia), Madagascar, and the Great Barrier Reef.
The diagram at the right graphically illustrates the ecosystem service synergies between mangroves, seagrasses, and coral reefs. The ecosystem services provided by intact reefs, seagrasses, and mangroves are both highly valuable and mutually enhance each other. Coastal protection (storm/wave attenuation) maintains the structure of adjacent ecosystems, and associated ecosystem services, in an offshore-to-onshore direction. Fisheries are characterized by migratory species, and therefore, protecting fisheries in one ecosystem increases fish biomass in others. Tourism benefits from coastal protection and healthy fisheries from multiple ecosystems. Here, we do not draw within-ecosystem connections in order to better emphasise synergies between systems.
Network ecology
![Intertidal food web highlighting nodes and links of artisanal fisheries and plankton](https://upload.wikimedia.org/wikipedia/commons/9/9e/Intertidal_food_web_highlighting_nodes_and_links_of_artisanal_fisheries_and_plankton.webp)
To compound things, removal of biomass from the ocean occurs simultaneously with multiple other stressors associated to climate change that compromise the capacity of these socio-ecological systems to respond to perturbations. Besides sea surface temperature, climate change also affects many other physical–chemical characteristics of marine
coastal waters
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
(stratification, acidification, ventilation)
as well as the wind regimes that control surface water productivity along the productive coastal upwelling ecosystems. Changes in the productivity of the oceans are reflected in changes of plankton biomass. Plankton contributes approximately half of the global primary production, supports marine food webs, influences the biogeochemical process in the ocean, and strongly affects commercial fisheries.
Indeed, an overall decrease in marine plankton productivity is expected over global scales.
Long-term increases and decreases in plankton productivity have already occurred over the past two decades along extensive regions of the Humboldt upwelling ecosystem off Chile, and are expected to propagate up the pelagic and benthic food webs.
Network ecology has advanced understanding of ecosystems by providing a powerful framework to analyse biological communities. Previous studies used this framework to assess food web robustness against species extinctions, defined as the fraction of initial species that remain present in the ecosystem after a primary extinction.
These studies showed the importance for food web persistence of highly connected species (independent of trophic position),
basal species,
and highly connected species that, at the same time, trophically support other highly connected species.
Most of these studies used a static approach, which stems from network theory and analyzes the impacts of structural changes on food webs represented by nodes (species) and links (interactions) that connect nodes, but ignores interaction strengths and population dynamics of interacting species.
Other studies used a dynamic approach, which considers not only the structure and intensity of interactions in a food web, but also the changes in species biomasses through time and the indirect effects that these changes have on other species.
Coastal biogeochemistry
Globally,
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
is one of the major environmental problems in coastal ecosystems. Over the last century the annual
riverine
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
inputs of
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
to the oceans have increased from 19 to 37
megatonnes
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
of nitrogen and from 2 to 4 megatonnes of phosphorus. Regionally, these increases were even more substantial as observed in the United States, Europe and China. In the Baltic Sea nitrogen and phosphorus loads increased by roughly a factor of three and six, respectively. The riverine nitrogen flux has increased by an order of magnitude to coastal waters of China within thirty years, while phosphorus export has tripled between 1970 and 2000.
Efforts to mitigate eutrophication through nutrient load reductions are hampered by the effects of
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
.
Changes in precipitation increase the runoff of N, P and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
(C) from land, which together with warming and increased dissolution alter the coupled marine nutrient and carbon cycles.
In contrast to the
open ocean
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
where
biogeochemical cycling
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
is largely dominated by
pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
processes driven primarily by
ocean circulation
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, s ...
, in the
coastal zone
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
, pelagic and benthic processes interact strongly and are driven by a complex and dynamic physical environment. Eutrophication in coastal areas leads to shifts toward rapidly growing opportunistic algae, and generally to a decline in benthic macrovegetation because of decreased light penetration, substrate change and more reducing sediments. Increased production and warming waters have caused expanding
hypoxia at the seafloor with a consequent loss of
benthic fauna. Hypoxic systems tend to lose many long-lived higher organisms and biogeochemical cycles typically become dominated by benthic bacterial processes and rapid pelagic turnover. However, if hypoxia does not occur, benthic fauna tends to increase in biomass with eutrophication.
![Vegetation and fauna processes controlling benthic biogeochemical fluxes](https://upload.wikimedia.org/wikipedia/commons/3/33/Vegetation_and_fauna_processes_controlling_benthic_biogeochemical_fluxes.jpg)
Changes in
benthic biota have far-reaching impacts on biogeochemical cycles in the coastal zone and beyond. In the
illuminated zone, benthic
microphyte
Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individu ...
s and
macrophytes mediate biogeochemical fluxes through
primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
, nutrient storage and
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
stabilization and act as a habitat and food source for a variety of animals, as shown in the diagram on the left above. Benthic animals contribute to biogeochemical transformations and fluxes between water and sediments both directly through their metabolism and indirectly by physically reworking the sediments and their porewaters and stimulating bacterial processes. Grazing on pelagic organic matter and biodeposition of feces and pseudofeces by suspension-feeding fauna increases organic matter sedimentation rates. In addition, nutrients and carbon are retained in biomass and transformed from organic to inorganic forms through metabolic processes.
Bioturbation
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a pr ...
, including sediment reworking and burrow ventilation activities (
bioirrigation
Bioirrigation refers to the process of benthos, benthic organisms flushing their burrows with overlying water. The exchange of dissolved substances between the porewater and overlying seawater that results is an important process in the context o ...
), redistributes particles and solutes within the sediment and enhances sediment-water fluxes of solutes. Bioturbation can also enhance resuspension of particles, a phenomenon termed "bioresuspension". Together, all these processes affect physical and chemical conditions at the sediment-water interface, and strongly influence organic matter degradation. When up-scaled to the ecosystem level, such modified conditions can significantly alter the functioning of coastal ecosystems and ultimately, the role of the coastal zone in filtering and transforming nutrients and carbon.
Artisan fisheries
Artisanal fisheries use simple fishing gears and small vessels.
Their activities tend to be confined to coastal areas. In general,
top-down and bottom-up forces determine ecosystem functioning and dynamics. Fisheries as a
top-down force can shorten and destabilise
food web
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one ...
s, while
effects driven by climate change can alter the bottom-up forces of
primary productivity
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
.
Direct human impacts and the full suite of drivers of global change are the main cause of species extinctions in
Anthropocene
The Anthropocene ( ) is a proposed geological epoch dating from the commencement of significant human impact on Earth's geology and ecosystems, including, but not limited to, anthropogenic climate change.
, neither the International Commissi ...
ecosystems,
with detrimental consequences on ecosystem functioning and their services to human societies. The world fisheries crisis is among those consequences, which cuts across fishing strategies, oceanic regions, species, and includes countries that have little regulation and those that have implemented rights-based co-management strategies to reduce
overharvesting
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term app ...
.
Chile has been one of the countries implementing Territorial Use Rights (TURFs) over an unprecedented geographic scale to manage the diverse coastal benthic resources using a co-management strategy.
These TURFS are used for artisanal fisheries. Over 60 coastal benthic species are actively harvested by these artisanal fisheries,
with species that are extracted from intertidal and shallow subtidal habitats.
The Chilean TURFs system brought significant improvements in sustainability of this complex socio-ecological system, helping to rebuild benthic
fish stocks,
improving fishers’ perception towards sustainability and increasing compliance9, as well as showing positive ancillary effects on conservation of biodiversity. However, the situation of most artisanal fisheries is still far from sustainable, and many fish stocks and coastal ecosystems show signs of
overexploitation
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term app ...
and ecosystem degradation, a consequence of the low levels of cooperation and low enforcement of TURF regulations, which leads to high levels of
free-riding and illegal fishing. It is imperative to improve understanding of the effects of these multi-species artisanal fisheries which simultaneously harvest species at all
trophic level
The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
s from kelp primary producers to top carnivores.
Remote sensing
Coastal zones are among the most populated areas on the planet. As the population continues to increase, economic development must expand to support human welfare. However, this development may damage the ability of the coastal environment to continue supporting human welfare for current and future generations. The management of complex coastal and marine social-ecological systems requires tools that provide frameworks with the capability of responding to current and emergent issues.
Remote data collection technologies include
satellite-based remote sensing,
aerial remote sensing,
unmanned aerial vehicles
An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
,
unmanned surface vehicle
Unmanned surface vehicles (USVs), also known as unmanned surface vessels, autonomous surface vehicles (ASVs) in some cases, uncrewed surface vessels (USVs), or colloquially drone ships, or robot boats, are boats or ships that operate on the ...
s,
unmanned underwater vehicle
Unmanned underwater vehicles (UUV), sometimes known as underwater drones, are submersible vehicles that can operate underwater without a human occupant. These vehicles may be divided into two categories: remotely operated underwater vehicles (ROU ...
s, and static sensors.
Frameworks have been developed that attempt to address and integrate these complex issues, such as the
Millennium Ecosystem Assessment
The Millennium Ecosystem Assessment (MA) is a major assessment of the human impact on the environment, called for by the United Nations Secretary-General Kofi Annan in 2000, launched in 2001 and published in 2005 with more than $14 million of gr ...
framework which links drivers, ecosystem services, and human welfare
However, obtaining the environmental data that is necessary to use such frameworks is difficult, especially in countries where access to reliable data and their dissemination are limited or non-existent and even thwarted.
Traditional techniques of point sampling and observation in the environment do deliver high information content, but they are expensive and often do not provide adequate spatial and temporal coverage, while remote sensing can provide cost-effective solutions, as well as data for locations where there is no or only limited information.
Coastal observing systems are typically nationally funded and built around national priorities. As a result, there are presently significant differences between countries in terms of sustainability, observing capacity and technologies, as well as methods and research priorities.
Ocean observing systems in coastal areas need to move toward integrated,
multidisciplinary
Interdisciplinarity or interdisciplinary studies involves the combination of multiple academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, anthropology, psychology, ec ...
and
multiscale systems, where heterogeneity can be exploited to deliver fit-for-purpose answers.
Essential elements of such distributed observation systems are the use of
machine-to-machine communication,
data fusion
Data fusion is the process of integrating multiple data sources to produce more consistent, accurate, and useful information than that provided by any individual data source.
Data fusion processes are often categorized as low, intermediate, or hig ...
and processing applying recent technological developments for the
Internet of Things
The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other comm ...
(IoT) toward a common
cyberinfrastructure United States federal research funders use the term cyberinfrastructure to describe research environments that support advanced data acquisition, data storage, data management, data integration, data mining, data visualization and other computing a ...
.
It has been argued that the standardisation that IoT brings to
wireless sensing will revolutionise areas like this.
Coastal areas are the most dynamic and productive parts of the oceans, which makes them a significant source of human resources and services. Coastal waters are located immediately in contact with human populations and exposed to anthropogenic disturbances, placing these resources and services under threat. These concerns explain why, in several coastal regions, a rapidly increasing number of observing systems have been implemented in the last decade. Expansion of coherent and sustained coastal observations has been fragmented and driven by national and regional policies and is often undertaken through short-term research projects. This results in significant differences between countries both in terms of sustainability and observing technologies, methods and research priorities.
Unlike the open ocean, where challenges are rather well-defined and stakeholders are fewer and well-identified, coastal processes are complex, acting on several spatial and temporal scales, with numerous and diversified users and stakeholders, often with conflicting interests. To adapt to such complexity coastal ocean observing system must be an integrated, multidisciplinary and multiscale system of systems.
Regime shifts
![Flow diagram of the Portuguese continental shelf ecosystem](https://upload.wikimedia.org/wikipedia/commons/a/a9/Flow_diagram_of_the_Portuguese_continental_shelf_ecosystem.jpg)
Marine ecosystems are affected by diverse pressures and consequently may undergo significant changes that can be interpreted as
regime shift
Regime shifts are large, abrupt, persistent changes in the structure and function of ecosystems, the climate, financial systems or other complex systems.Lewontin, R. (1969) Meaning of Stability. ''Brookhaven Sym Biol'', 13Holling, C.S. (1973) Resil ...
s.
Marine ecosystems worldwide are affected by increasing natural and anthropogenic pressures and consequently undergo significant changes at unprecedented rates. Affected by these changes, ecosystems can reorganise and still maintain the same function, structure, and identity.
However, under some circumstances, the ecosystem may undergo changes that modify the system’s structure and function and this process can be described as a shift to a new regime.
Usually, a regime shift is triggered by large-scale climate-induced variations, intense fishing exploitation or both. Criteria used to define regime shifts vary and the changes that have to occur in order to consider that a system has undergone a regime shift are not well-defined.
Normally, regime shifts are defined as high amplitude, low-frequency and often abrupt changes in species abundance and community composition that are observed at multiple trophic levels (TLs).
These changes are expected to occur on a large spatial scale and take place concurrently with physical changes in the climate system.
Regime shifts have been described in several marine ecosystems including Northern
Benguela
Benguela (; Umbundu: Luombaka) is a city in western Angola, capital of Benguela Province. Benguela is one of Angola's most populous cities with a population of 555,124 in the city and 561,775 in the municipality, at the 2014 census.
History
Por ...
,
the North Sea, and the Baltic Sea. In large
upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
ecosystems, it is common to observe
decadal fluctuations in
species abundance
In ecology, local abundance is the relative representation of a species in a particular ecosystem. It is usually measured as the number of individuals found per sample. The ratio of abundance of one species to one or multiple other species livin ...
and their replacements. These fluctuations might be irreversible and might be an indicator of the new regime, as was the case in the Northern Benguela ecosystem.
However, changes in the upwelling systems might be interpreted as fluctuations within the limits of natural variability for an ecosystem, and not as an indicator of the regime shift.
The Portuguese continental shelf ecosystem (PCSE) constitutes the northernmost part of the
Canary Current
The Canary Current is a wind-driven surface current that is part of the North Atlantic Gyre. This eastern boundary current branches south from the North Atlantic Current and flows southwest about as far as Senegal where it turns west and later jo ...
Upwelling System and is characterised by seasonal upwelling that occurs during the spring and summer as a result of steady northerly winds. It has recently changed in the abundance of coastal pelagic species such as
sardine
"Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the Ital ...
,
chub mackerel
The chub mackerel, Pacific mackerel, or Pacific chub mackerel (''Scomber japonicus'') is a species of fish in the tuna and mackerel family, Scombridae. This species of mackerel closely resembles the Atlantic chub mackerel.
Characteristics
The chu ...
,
horse mackerel
Horse mackerel is a vague vernacular term for a range of species of fish throughout the English-speaking world. It is commonly applied to pelagic fishes, especially of the Carangidae (jack mackerels and scads) family, most commonly those of the gen ...
,
blue jack mackerel and
anchovy
An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water.
More than 140 species are placed in 1 ...
. Moreover, in the last decades, an increase in higher trophic level species has been documented. The causes underlying changes in the pelagic community are not clear but it has been suggested that they result from a complex interplay between environmental variability, species interactions and
fishing pressure
Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...
.
There is evidence, that changes in the intensity of the Iberian coastal upwelling (resulting from the strengthening or weakening northern winds) had occurred in the last decades. However, the character of these changes is contradictory where some authors observed intensification of upwelling-favourable winds while others documented their weakening. A 2019 review of upwelling rate and intensity along the Portuguese coast documented a successive weakening of the upwelling since 1950 that lasted till mid/late 1970s in the north-west and south-west and till 1994 in the south coast.
An increase in upwelling index over the period 1985–2009 was documented in all studied regions while additionally upwelling intensification were observed in the south.
A continuous increase in water temperature, ranging from 0.1 to 0.2 °C per decade has also been documented.
Threats and decline
![Nørre Vorupør Coast one third sky 2012-11-18](https://upload.wikimedia.org/wikipedia/commons/b/b0/N%C3%B8rre_Vorup%C3%B8r_Coast_one_third_sky_2012-11-18.jpg)
Many marine fauna utilise coastal habitats as critical nursery areas, for shelter and feeding, yet these habitats are increasingly at risk from agriculture, aquaculture, industry and urban expansion. Indeed, these systems are subject to what may be called "a triple whammy" of increasing industrialisation and urbanisation, an increased loss of biological and physical resources (fish, water, energy, space), and a decreased resilience to the
consequences of a warming climate and
sea level rise
Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
. This has given rise to the complete loss, modification or disconnection of natural coastal ecosystems globally. For example, almost 10% of the entire
Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
coastline in Australia (2,300 km) has been replaced with urban infrastructure (e.g., rock seawalls, jetties, marinas), causing massive loss and fragmentation of sensitive coastal ecosystems. Global loss of seagrass reached around 7% of seagrasses area per year by the end of the twentieth century. A global analysis of tidal wetlands (
mangroves
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in several ...
,
tidal flats
Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
, and
tidal marshes) published in 2022 estimated global losses of from 1999-2019, however, this study also estimated that these losses were largely offset by the establishment of of new tidal wetlands that were not present in 1999.
Approximately three-quarters of the net decrease between 1999 and 2019 occurred in Asia (74.1%), with 68.6% concentrated in three countries:
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
(36%),
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
(20.6%), and
Myanmar
Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
(12%).
Of these global tidal wetland losses and gains, 39% of losses and 14% of gains were attributed to direct human activities.
Approximately 40% of the global mangrove has been lost since the 1950's
with more than 9,736 km
2 of the world's mangroves continuing to be degraded in the 20 years period between 1996 and 2016. Saltmarshes are drained when coastal land is claimed for agriculture, and deforestation is an increasing threat to shoreline vegetation (such as mangroves) when coastal land is appropriated for urban and industrial development,
both of which may result in the degradation of
blue carbon storages and increasing greenhouse gas emissions.
These accumulating pressures and impacts on coastal ecosystems are neither isolated nor independent, rather they are synergistic, with feedbacks and interactions that cause individual effects to be greater than their sums. In the year before the ecosystem restoration Decade commences, there is a critical knowledge deficit inhibiting an appreciation of the complexity of coastal ecosystems that hampers the development of responses to mitigate continuing impacts—not to mention uncertainty on projected losses of coastal systems for some of the worst-case future climate change scenarios.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Restoration
![UN Decade on Ecosystem Restoration 2021 to 2030 – coastal ecosystems](https://upload.wikimedia.org/wikipedia/commons/7/78/UN_Decade_on_Ecosystem_Restoration_2021_to_2030_%E2%80%93_coastal_ecosystems.jpg)
The United Nations has declared 2021–2030 the
UN Decade on Ecosystem Restoration
The United Nations Decade on Ecosystem Restoration runs from 2021 to 2030. Similar to other nature related international decades, its purpose is to promote the United Nation's environmental goals. Specifically, to facilitate global cooperation for ...
. This call to action has the purpose of recognising the need to massively accelerate global restoration of degraded ecosystems, to fight the climate heating crisis, enhance food security, provide clean water and protect biodiversity on the planet. The scale of restoration will be key. For example, the
Bonn Challenge The Bonn Challenge is a global effort to restore 150 million hectares of the world's degraded and deforested lands by 2020 and 350 million hectares by 2030. It was hosted and launched by Germany and the International Union for Conservation of Nature ...
has the goal to restore 350 million km
2, about the size of India, of degraded terrestrial ecosystems by 2030. However, international support for restoration of
blue coastal ecosystems, which provide an impressive array of benefits to people, has lagged.
The diagram on the right shows the current state of modified and impacted coastal ecosystems and the expected state following the decade of restoration.
Also, shown is the uncertainty in the success of past restoration efforts, current state of altered systems, climate variability, and restoration actions that are available now or on the horizon. This could mean that delivering the Decade on Ecosystem Restoration for coastal systems needs to be viewed as a means of getting things going where the benefits might take longer than a decade.
Only the Global Mangrove Alliance comes close to the Bonn Challenge, with the aim of increasing the global area of mangroves by 20% by 2030.
However, mangrove scientists have reservations about this target, voicing concerns that it is unrealistic and may prompt inappropriate practices in attempting to reach this target.
Conservation and connectivity
There has recently been a perceptual shift away from habitat representation as the sole or primary focus of conservation prioritisation, towards consideration of ecological processes that shape the distribution and abundance of biodiversity features.
In marine ecosystems, connectivity processes are paramount,
and designing systems of marine protected areas that maintain connectivity between habitat patches has long been considered an objective of conservation planning.
Two forms of connectivity are critical to structuring coral reef fish populations: dispersal of larvae in the pelagic environment, and post-settlement migration by individuals across the seascape. Whilst a growing literature has described approaches for considering larval connectivity in conservation prioritisation, relatively less attention has been directed towards developing and applying methods for considering post-settlement connectivity
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Seascape connectivity (connectedness among different habitats in a seascape, c.f. among patches of the same habitat type
is essential for species that utilise more than one habitat, either during diurnal movements or at different stages in their life history. Mangroves, seagrass beds, and lagoon reefs provide nursery areas for many commercially and ecologically important fish species that subsequently make
ontogenetic
Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...
shifts to adult populations on coral reefs.
These back-reef habitats are often overlooked for conservation or management in favour of coral reefs that support greater adult biomass, yet they can be equally if not more at risk from habitat degradation and loss.
Even where juveniles are not targeted by fishers, they can be vulnerable to habitat degradation, for example from sedimentation caused by poor land-use practices.
There is clear empirical evidence that proximity to nursery habitats can enhance the effectiveness (i.e. increasing the abundance, density, or biomass of fish species) of marine protected areas on coral reefs.
For example, at study sites across the western Pacific, the abundance of harvested fish species was significantly greater on protected reefs close to mangroves, but not on protected reefs isolated from mangroves.
The functional role of herbivorous fish species that perform ontogenetic migrations may also enhance the resilience of coral reefs close to mangroves.
Despite this evidence, and widespread calls to account for connectivity among habitats in the design of spatial management,
there remain few examples where seascape connectivity is explicitly considered in spatial conservation prioritisation (the analytical process of identifying priority areas for conservation or management actions).
See also
*
Blue carbon
Blue Carbon refers to organic carbon that is captured and stored by the world's oceanic and coastal ecosystems, mostly by algae, seagrasses, macroalgae, mangroves, salt marshes and other plants in coastal wetlands. The term Blue Carbon was coined ...
*
Coast
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
*
Coastal biogeomorphology
Since the 1990s, biogeomorphology has developed as an established research field examining the interrelationship between organisms and geomorphic processes in a variety of environments, both marine, and terrestrial.Naylor, Larissa A. (2005) ''The ...
*
Shallow water marine environment
Shallow water marine environment refers to the area between the shore and deeper water, such as a reef wall or a shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this ...
*
Tides in marginal seas
References
Further reading
*
{{Modelling ecosystems, expanded=none
Ecosystems
Biological oceanography