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Kelp forests are underwater areas with a high density of
kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...
, 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
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s on Earth.Mann, K.H. 1973. Seaweeds: their productivity and strategy for growth. Science 182: 975-981. Although algal kelp forest combined with
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
s only cover 0.1% of Earth's total surface, they account for 0.9% of global primary productivity. 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 Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...
coastal oceans. 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 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 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 ...
nearshore ecosystems, which can release
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
s from their normal population regulation and result in the overgrazing 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 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 ...
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 ...
, kelp forests have almost 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 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.


Kelp

The term
kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...
refers to marine algae belonging to the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Laminariales (phylum:
Ochrophyta The ochrophytes, subphylum Ochrophytina, is a group of mostly photosynthetic heterokonts. Their plastid is of red algal origin. The classification of the group is still being worked out. Originally, the ochrophytes were regarded as a phylum ...
). Though not considered a taxonomically diverse order, kelps are highly diverse structurally and functionally. The most widely recognized species are the giant kelps ('' Macrocystis'' spp.), although numerous other genera such as ''
Laminaria ''Laminaria'' is a genus of brown seaweed in the order Laminariales (kelp), comprising 31 species native to the north Atlantic and northern Pacific Oceans. This economically important genus is characterized by long, leathery laminae and relati ...
'', '' Ecklonia'', '' Lessonia'', ''
Nereocystis ''Nereocystis'' (Greek, 'mermaid's bladder') is a monotypic genus of subtidal kelp containing the species ''Nereocystis luetkeana''. Some English names include edible kelp, bull kelp, bullwhip kelp, ribbon kelp, bladder wrack, and variations of ...
'', '' Alaria'', and '' Eisenia'' are described. A wide range of sea life uses kelp forests for protection or food, including fish. In the North Pacific kelp forests, particularly rockfish, and many
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s, such as
amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
s,
shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
, marine snails, bristle worms, and brittle stars. Many marine mammals and birds are also found, including seals, sea lions, whales,
sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the smal ...
s, gulls, terns,
snowy egret The snowy egret (''Egretta thula'') is a small white heron. The genus name comes from Provençal French for the little egret, , which is a diminutive of , 'heron'. The species name ''thula'' is the Araucano term for the black-necked swan, a ...
s,
great blue heron The great blue heron (''Ardea herodias'') is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North America and Central America, as well as the Caribbean and the Galápagos I ...
s, and cormorants, as well as some shore birds. Frequently considered an
ecosystem engineer 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 engin ...
, kelp provides a physical substrate and habitat for kelp forest communities. In algae (kingdom
Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...
), the body of an individual organism is known as a
thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...
rather than as a plant (kingdom Plantae). The morphological structure of a kelp thallus is defined by three basic structural units: * The holdfast is a root-like mass that anchors the thallus to the sea floor, though unlike true roots it is not responsible for absorbing and delivering nutrients to the rest of the thallus. * The stipe is analogous to a plant stalk, extending vertically from the holdfast and providing a support framework for other morphological features. * The fronds are leaf- or blade-like attachments extending from the stipe, sometimes along its full length, and are the sites of nutrient uptake and photosynthetic activity. In addition, many kelp species have
pneumatocyst In phycology, a pneumatocyst is a floating structure that contains gas found on brown seaweed. A seaweed's thallus may have more than one. They provide buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that oppose ...
s, or gas-filled bladders, usually located at the base of fronds near the stipe. These structures provide the necessary buoyancy for kelp to maintain an upright position in the water column. The environmental factors necessary for kelp to survive include hard substrate (usually rock or sand), high nutrients (e.g., nitrogen, phosphorus), and light (minimum annual
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
dose > 50 E m−2Druehl, L.D. 1981. The distribution of Laminariales in the North Pacific with reference to environmental influences. Proceedings of the International Congress on Systematic Evolution and Biology 2: 248-256.). Especially productive kelp forests tend to be associated with areas of significant oceanographic
upwelling Upwelling is an physical oceanography, 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 ...
, a process that delivers cool, nutrient-rich water from depth to the ocean's mixed surface layer. Water flow and turbulence facilitate nutrient assimilation across kelp fronds throughout the water column. Water clarity affects the depth to which sufficient light can be transmitted. In ideal conditions, giant kelp (''Macrocystis'' spp.) can grow as much as 30–60 cm vertically per day. Some species, such as ''Nereocystis'', are annuals, while others such as ''Eisenia'' are
perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widel ...
s, living for more than 20 years. In perennial kelp forests, maximum growth rates occur during upwelling months (typically spring and summer) and die-backs correspond to reduced nutrient availability, shorter photoperiods, and increased storm frequency. Kelps are primarily associated with
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
arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
waters worldwide. Of the more dominant genera, ''Laminaria'' is mainly associated with both sides of the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
and the coasts of
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
and
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
; ''Ecklonia'' is found in
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
,
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
, and
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
; and ''Macrocystis'' occurs throughout the northeastern and southeastern
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...
,
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-smal ...
archipelagos, and in patches around Australia, New Zealand, and South Africa. The region with the greatest diversity of kelps (>20 species) is the northeastern Pacific, from north of
San Francisco, California San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17t ...
, to the
Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...
, Alaska. Although kelp forests are unknown in tropical surface waters, a few species of ''Laminaria'' have been known to occur exclusively in tropical deep waters. This general absence of kelp from the tropics is believed to be mostly due to insufficient nutrient levels associated with warm, oligotrophic waters. One recent study spatially overlaid the requisite physical parameters for kelp with mean oceanographic conditions and produced a model predicting the existence of subsurface kelps throughout the tropics worldwide to depths of . For a hotspot in the Galapagos Islands, the local model was improved with fine-scale data and tested; the research team found thriving kelp forests in all eight of their sampled sites, all of which had been predicted by the model, thus validated their approach. This suggests that their global model might actually be fairly accurate, and if so, kelp forests would be prolific in tropical subsurface waters worldwide. The importance of this contribution has been rapidly acknowledged within the scientific community and has prompted an entirely new trajectory of kelp forest research, highlighting the potential for kelp forests to provide marine organisms spatial refuge under climate change and providing possible explanations for evolutionary patterns of kelps worldwide.


Ecosystem architecture

The architecture of a kelp forest ecosystem is based on its physical structure, which influences the associated species that define its community structure. Structurally, the ecosystem includes three guilds of kelp and two guilds occupied by other algae: *Canopy kelps include the largest species and often constitute floating canopies that extend to the ocean surface (e.g., ''Macrocystis'' and ''Alaria''). *Stipitate kelps generally extend a few meters above the sea floor and can grow in dense aggregations (e.g., ''Eisenia'' and ''Ecklonia''). *Prostrate kelps lie near and along the sea floor (e.g., ''Laminaria''). *The
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...
assemblage is composed of other algal species (e.g., filamentous and foliose functional groups, articulated corallines) and sessile organisms along the ocean bottom. *Encrusting coralline algae directly and often extensively cover geologic substrate. Multiple kelp species often co-exist within a forest; the term understory canopy refers to the stipitate and prostrate kelps. For example, a ''Macrocystis'' canopy may extend many meters above the seafloor towards the ocean surface, while an understory of the kelps ''Eisenia'' and ''Pterygophora'' reaches upward only a few meters. Beneath these kelps, a benthic assemblage of foliose red algae may occur. The dense vertical infrastructure with overlying canopy forms a system of microenvironments similar to those observed in a terrestrial forest, with a sunny canopy region, a partially shaded middle, and darkened seafloor. Each guild has associated organisms, which vary in their levels of dependence on the habitat, and the assemblage of these organisms can vary with kelp morphologies.Foster, M.S. and D.R. Schiel. 1985. The ecology of giant kelp forests in California: a community profile. US Fish and Wildlife Service Report 85: 1-152.Graham, M.H. 2004. Effects of local deforestation on the diversity and structure of Southern California giant kelp forest food webs. Ecosystems 7: 341-357. For example, in California, ''Macrocystis pyrifera'' forests, the nudibranch '' Melibe leonina'', and
skeleton shrimp Caprellidae is a family of amphipods commonly known as skeleton shrimps. Their common name denotes the threadlike slender body which allows them to virtually disappear among the fine filaments of seaweed, hydroids and bryozoans. They are sometime ...
''Caprella californica'' are closely associated with surface canopies; the kelp perch ''Brachyistius frenatus'', rockfish '' Sebastes'' spp., and many other fishes are found within the stipitate understory; brittle stars and turban snails '' Tegula'' spp. are closely associated with the kelp holdfast, while various herbivores, such as sea urchins and abalone, live under the prostrate canopy; many seastars, hydroids, and
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...
fishes live among the benthic assemblages; solitary corals, various gastropods, and
echinoderms An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...
live over the encrusting coralline algae. In addition,
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 re ...
es and
marine mammals 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 ...
are loosely associated with kelp forests, usually interacting near the edges as they visit to feed on resident organisms.


Trophic ecology

Classic studies in kelp forest ecology have largely focused on trophic interactions (the relationships between organisms and their
food webs 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 ...
), particularly the understanding and top-down trophic processes. Bottom-up processes are generally driven by the abiotic conditions required for primary producers to grow, such as availability of light and nutrients, and the subsequent transfer of energy to consumers at higher trophic levels. For example, the occurrence of kelp is frequently correlated with oceanographic upwelling zones, which provide unusually high concentrations of nutrients to the local environment.Dayton, P.K. M.J. Tegner, P.B. Edwards and K.L. Riser. 1999. Temporal and spatial scales of kelp demography: the role of the oceanographic climate. Ecological Monographs 69: 219-250. This allows kelp to grow and subsequently support herbivores, which in turn support consumers at higher
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 ...
s.Carr, M.H. 1994. Effects of macroalgal dynamics on recruitment of a temperate reef fish. Ecology 75: 1320-1333. By contrast, in top-down processes, predators limit the biomass of species at lower trophic levels through consumption. In the absence of predation, these lower-level species flourish because resources that support their energetic requirements are not limiting. In a well-studied example from Alaskan kelp forests, Estes, J.A. and D.O. Duggins. 1995. Sea otters and kelp forests in Alaska: generality and variation in a community ecological paradigm. Ecological Monographs 65: 75-100. sea otters (''Enhydra lutris'') control populations of herbivorous
sea urchins Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
through predation. When sea otters are removed from the ecosystem (for example, by human exploitation), urchin populations are released from predatory control and grow dramatically. This leads to increased herbivore pressure on local kelp stands. Deterioration of the kelp itself results in the loss of physical ecosystem structure and subsequently, the loss of other species associated with this habitat. In Alaskan kelp forest ecosystems, sea otters are the
keystone species A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
that mediates this trophic cascade. In Southern California, kelp forests persist without sea otters and the control of herbivorous urchins is instead mediated by a suite of predators including lobsters and large fishes, such as the California sheephead. The effect of removing one predatory species in this system differs from Alaska because redundancy exists in the trophic levels and other predatory species can continue to regulate urchins. However, the removal of multiple predators can effectively release urchins from predator pressure and allow the system to follow trajectories towards kelp forest degradation.Pearse, J.S. and A.H. Hines. 1987. Expansion of a central California kelp forest following the mass mortality of sea urchins. Marine Biology 51: 83-91. Similar examples exist in
Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...
, South Africa, Australia, and Chile. The relative importance of top-down versus bottom-up control in kelp forest ecosystems and the strengths of trophic interactions continue to be the subject of considerable scientific investigation.Sala, E. and M.H. Graham. 2002. Community-wide distribution of predator-prey interaction strength in kelp forests. Proceedings of the National Academy of Sciences 99: 3678-3683.Halpern, B.S., K. Cottenie and B.R. Broitman. 2006. Strong top-down control in Southern California kelp forest ecosystems. Science 312: 1230-1232. The transition from macroalgal (i.e. kelp forest) to denuded landscapes dominated by sea urchins (or ‘ urchin barrens’) is a widespread phenomenon, often resulting from trophic cascades like those described above; the two phases are regarded as alternative stable states of the ecosystem.Dayton, P.K., M.J. Tegner, P.E. Parnell and P.B. Edwards. 1992. Temporal and spatial patterns of disturbance and recovery in a kelp forest community. Ecological Monographs 62: 421-445. The recovery of kelp forests from barren states has been documented following dramatic perturbations, such as urchin disease or large shifts in thermal conditions.Vásquez, J.A., J.M. Alonso Vega and A.H. Buschmann. 2006. Long term variability in the structure of kelp communities in northern Chile and the 1997-98 ENSO. Journal of Applied Phycology 18: 505-519. Recovery from intermediate states of deterioration is less predictable and depends on a combination of abiotic factors and biotic interactions in each case. Though urchins are usually the dominant herbivores, others with significant interaction strengths include seastars, isopods, kelp crabs, and herbivorous fishes. In many cases, these organisms feed on kelp that has been dislodged from substrate and drifts near the ocean floor rather than expend energy searching for intact thalli on which to feed. When sufficient drift kelp is available, herbivorous grazers do not exert pressure on attached plants; when drift subsidies are unavailable, grazers directly impact the physical structure of the ecosystem.Ebeling, A.W., D.R. Laur and R.J. Rowley. 1985. Severe storm disturbances and reversal of community structure in a southern California kelp forest. Marine Biology 84: 287-294. Many studies in Southern California have demonstrated that the availability of drift kelp specifically influences the foraging behavior of sea urchins.Dayton, P.K. and M.J. Tegner. 1984. Catastrophic storms, El Niño, and patch stability in a southern California kelp community. Science 224: 283-285. Drift kelp and kelp-derived particulate matter have also been important in subsidizing adjacent habitats, such as sandy beaches and the rocky intertidal.


Patch dynamics

Another major area of kelp forest research has been directed at understanding the spatial-temporal patterns of kelp patches. Not only do such dynamics affect the physical landscape, but they also affect species that associate with kelp for refuge or foraging activities. Large-scale environmental disturbances have offered important insights concerning mechanisms and ecosystem
resilience Resilience, resilient, resiliency, or ''variation'', may refer to: Science Ecology * Ecological resilience, the capacity of an ecosystem to recover from perturbations ** Climate resilience, the ability of systems to recover from climate change * ...
. Examples of environmental disturbances include: *Acute and chronic
pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...
events have been shown to impact southern California kelp forests, though the intensity of the impact seems to depend on both the nature of the contaminants and duration of exposure. Pollution can include sediment deposition 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 phyt ...
from sewage, industrial byproducts and contaminants like PCBs and heavy metals (for example, copper, zinc), runoff of
organophosphates In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...
from agricultural areas, anti-fouling chemicals used in harbors and marinas (for example, TBT and creosote) and land-based pathogens like fecal coliform bacteria. *Catastrophic storms can remove surface kelp canopies through wave activity, but usually leave understory kelps intact; they can also remove urchins when little spatial refuge is available. Interspersed canopy clearings create a seascape mosaic where sunlight penetrates deeper into the kelp forest and species that are normally light-limited in the understory can flourish. Similarly, substrate cleared of kelp holdfasts can provide space for other sessile species to establish themselves and occupy the seafloor, sometimes directly competing with juvenile kelp and even inhibiting their settlement. :*
El Niño-Southern Oscillation EL, El or el may refer to: Religion * El (deity), a Semitic word for "God" People * EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer * El DeBarge, music artist * El Franco Lee (1949–2016), American ...
(ENSO) events involve the depression of oceanographic thermoclines, severe reductions of nutrient input, and changes in storm patterns. Stress due to warm water and
nutrient depletion Nutrient depletion is a form of resource depletion and refers to the loss of nutrients and micronutrients in a habitat or parts of the biosphere, most often the soil (soil depletion, soil degradation). On the level of a complete ecological niche or ...
can increase the susceptibility of kelp to storm damage and herbivorous grazing, sometimes even prompting phase shifts to urchin-dominated landscapes. In general, oceanographic conditions (that is, water temperature, currents) influence the recruitment success of kelp and its competitors, which clearly affect subsequent species interactions and kelp forest dynamics. *Overfishing higher trophic levels that naturally regulate herbivore populations is also recognized as an important stressor in kelp forests.Jackson, J.B.C, M.X. Kirby, W.H. Berger, K.A. Bjorndal, L.W. Botsford, B.J. Bourque, R.H. Bradbury, R. Cooke, J. Erlandson, J.A. Estes, T.P. Hughes, S. Kidwell, C.B. Lange, H.S. Lenihan, J.M. Pandolfi, C.H. Peterson, R.S. Steneck, M.J. Tegner and R.R. Warner. 2002. Historical overfishing and the recent collapse of coastal ecosystems. Science 293: 629-638. As described in the previous section, the drivers and outcomes of trophic cascades are important for understanding spatial-temporal patterns of kelp forests. In addition to ecological monitoring of kelp forests before, during, and after such disturbances, scientists try to tease apart the intricacies of kelp forest dynamics using experimental manipulations. By working on smaller spatial-temporal scales, they can control for the presence or absence of specific biotic and abiotic factors to discover the operative mechanisms. For example, in southern Australia, manipulations of kelp canopy types demonstrated that the relative amount of ''Ecklonia radiata'' in a canopy could be used to predict understory species assemblages; consequently, the proportion of ''E. radiata'' can be used as an indicator of other species occurring in the environment.


Human use

Kelp forests have been important to human existence for thousands of years. Indeed, many now theorise that the first colonisation of the Americas was due to fishing communities following the Pacific kelp forests during the last ice age. One theory contends that the kelp forests that would have stretched from northeast Asia to the American Pacific coast would have provided many benefits to ancient boaters. The kelp forests would have provided many sustenance opportunities, as well as acting as a type of buffer from rough water. Besides these benefits, researchers believe that the kelp forests might have helped early boaters navigate, acting as a type of "kelp highway". Theorists also suggest that the kelp forests would have helped these ancient colonists by providing a stable way of life and preventing them from having to adapt to new ecosystems and develop new survival methods even as they traveled thousands of miles. Modern economies are based on
fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, ...
of kelp-associated species such as
lobster Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...
and rockfish. Humans can also harvest kelp directly to feed aquaculture species such as
abalone Abalone ( or ; via Spanish , from Rumsen ''aulón'') is a common name for any of a group of small to very large marine gastropod molluscs in the family Haliotidae. Other common names are ear shells, sea ears, and, rarely, muttonfish or mutto ...
and to extract the compound alginic acid, which is used in products like toothpaste and antacids. Kelp forests are valued for recreational activities such as
SCUBA diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for " Self-Contained Underwater Breathing Apparatus", was coined by Chr ...
and
kayaking Kayaking is the use of a kayak for moving over water. It is distinguished from canoeing by the sitting position of the paddler and the number of blades on the paddle. A kayak is a low-to-the-water, canoe-like boat in which the paddler sits faci ...
; the industries that support these sports represent one benefit related to the ecosystem and the enjoyment derived from these activities represents another. All of these are examples of
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. ...
provided specifically by kelp forests. The Monterey Bay aquarium was the first aquarium to exhibit an alive kelp forest.


As carbon sequesters

Kelp forests grow in rocky places along the shore that are constantly eroding carrying material out to the deep sea. The kelp then sinks to the ocean floor and store the carbon where is it unlikely to be disturbed by human activity. Researchers from the
University of Western Australia The University of Western Australia (UWA) is a public research university in the Australian state of Western Australia. The university's main campus is in Perth, the state capital, with a secondary campus in Albany and various other facilitie ...
estimated kelp forest around Australia sequestered 1.3-2.8 teragrams of carbon per year which is 27–34% of the total annual
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 coine ...
sequestered in the Australian continent by tidal marshes, mangrove forests and seagrass beds. Every year 200 million tons of carbon dioxide are being sequestered by macroalgae such as kelp.


Threats and management

Given the complexity of kelp forests – their variable structure, geography, and interactions – they pose a considerable challenge to environmental managers. Extrapolating even well-studied trends to the future is difficult because interactions within the ecosystem will change under variable conditions, not all relationships in the ecosystem are understood, and the nonlinear thresholds to transitions are not yet recognized. With respect to kelp forests, major issues of concern include marine pollution and
water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
, kelp harvesting and fisheries,
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
, 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 ...
. The most pressing threat to kelp forest preservation may be the overfishing of coastal ecosystems, which by removing higher trophic levels facilitates their shift to depauperate urchin barrens. The maintenance of
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity'') ...
is recognized as a way of generally stabilizing ecosystems and their services through mechanisms such as functional compensation and reduced susceptibility to foreign species invasions. More recently, the 2022 IPCC report states that kelp and other seaweeds in most regions are undergoing mass mortalities from high temperature extremes and range shifts from warming, as they are stationary and cannot adapt quick enough to deal with the rapidly increasing temperature of the Earth and thus, the ocean. In many places, managers have opted to regulate the harvest of kelp and/or the taking of kelp forest species by fisheries. While these may be effective in one sense, they do not necessarily protect the entirety of the ecosystem. Marine protected areas (MPAs) offer a unique solution that encompasses not only target species for harvesting, but also the interactions surrounding them and the local environment as a whole. Direct benefits of MPAs to fisheries (for example, spillover effects) have been well documented around the world. Indirect benefits have also been shown for several cases among species such as abalone and fishes in Central California. Most importantly, MPAs can be effective at protecting existing kelp forest ecosystems and may also allow for the regeneration of those that have been affected.


Kelp forest restoration in California

In the 2010s, Northern California lost 95% of its kelp ecosystems due to marine heatwaves. Kelp bed recovery efforts in California are primarily focusing on
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) o ...
removal, both by scuba divers, and by
sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the smal ...
s, which are natural predators. A brown algae, '' Sargassum horneri'', an invasive species first spotted in 2003, has also been a concern. Researchers at the Bodega Marine Laboratory of UC Davis are developing replanting strategies, and volunteers of the Orange County Coastkeeper group are replanting giant kelp. Humboldt State University began cultivating bull kelp in its research farm in 2021. Research efforts at the state level to prevent kelp forest collapse in California were announced in July 2020. At the federal level, H.R. 4458, the Keeping Ecosystems Living and Productive (KELP) Act, introduced July 29, 2021, seeks to establish a new grant program within
NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
for kelp forest restoration.


See also

* Aquaculture of giant kelp


References


External links

* * Excellent general information on kelp forests, as well as specific information on Tasmanian kelp forests. * Watch a live feed from the kelp forest exhibit. {{Authority control Aquatic ecology Fishing industry Brown algae