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 syste ...
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 colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
s only cover 0.1% of Earth's total surface, they account for 0.9% of global
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 ...
. 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 c ...
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.]
![Kelp forest distribution map](https://upload.wikimedia.org/wikipedia/commons/5/5a/Kelp_forest_distribution_map.png)
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 ...
, 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. 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.
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
Marine primary production is the chemical synthesis in the ocean of organic compounds from atmospheric or dissolved carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it al ...
belonging to the
order 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 d ...
). Though not considered a taxonomically diverse order, kelps are highly diverse structurally and functionally.
The most widely recognized species are the giant kelps (''
Macrocystis
''Macrocystis'' is a monospecific genus of kelp (large brown algae). This genus contains the largest of all the phaeophyceae or brown algae. ''Macrocystis'' has pneumatocysts at the base of its blades. Sporophytes are perennial and the indi ...
'' 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
''Ecklonia'' is a genus of kelp (brown algae) belonging to the family Lessoniaceae.
The genus name of ''Ecklonia'' is in honour of Christian Friedrich Ecklon (1795–1868), who was a Danish botanical collector and apothecary.
The genus was cir ...
'', ''
Lessonia'', ''
Nereocystis'', ''
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
Rockfish is a common term for several species of fish, referring to their tendency to hide among rocks.
The name rockfish is used for many kinds of fish used for food. This common name belongs to several groups that are not closely related, and ca ...
, 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 chordate ...
s, such as
amphipods,
shrimp,
marine snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...
s,
bristle worm
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...
s, and
brittle star
Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...
s. Many marine mammals and birds are also found, including seals, sea lions, whales,
sea otters, gulls, terns,
snowy egrets,
great blue herons, and cormorants, as well as some shore birds.
Frequently considered an
ecosystem engineer, 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 exc ...
), 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
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
). 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
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
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 to lift the blades toward the surface, allowing them to receive more sunlight for p ...
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 dose > 50 E m
−2[Druehl, 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 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 nut ...
, 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
annual
Annual may refer to:
*Annual publication, periodical publications appearing regularly once per year
** Yearbook
** Literary annual
*Annual plant
*Annual report
*Annual giving
*Annual, Morocco, a settlement in northeastern Morocco
*Annuals (band), ...
s, 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 wid ...
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 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 (Greenland), Finland, Iceland, N ...
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 and
Japan; ''Ecklonia'' is found in
Australia,
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 count ...
, and
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
; 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 contin ...
,
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-small ...
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 17th ...
, 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,
oligotroph
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...
ic 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
![Giantkelp2 300](https://upload.wikimedia.org/wikipedia/commons/9/9a/Giantkelp2_300.jpg)
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 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
Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...
''
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 sometim ...
''Caprella californica'' are closely associated with surface canopies; the kelp perch ''Brachyistius frenatus'', rockfish ''
Sebastes
''Sebastes'' is a genus of marine ray-finned fish belonging to the subfamily Sebastinae part of the family Scorpaenidae, most of which have the common name of rockfish. A few are called ocean perch, sea perch or redfish instead. They are found ...
'' spp., and many other fishes are found within the stipitate understory;
brittle stars
Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...
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 fishes live among the benthic assemblages; solitary corals, various
gastropods
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...
, and
echinoderms 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 re ...
are loosely associated with kelp forests, usually interacting near the edges as they visit to feed on resident organisms.
Trophic ecology
![Calliostoma annulatum](https://upload.wikimedia.org/wikipedia/commons/2/21/Calliostoma_annulatum.jpg)
Classic studies in kelp forest ecology have largely focused on trophic interactions (the relationships between organisms and their
food webs), 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
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 smalle ...
(''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 that mediates this
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 ...
. 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 California sheephead (''Semicossyphus pulcher'') is a species of wrasse native to the eastern Pacific Ocean. Its range is from Monterey Bay, California, to the Gulf of California, Mexico. It can live for up to 20 years in favorable condition ...
. 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
An urchin barren is an area of the shallow part of the ocean where the population growth of sea urchins has gone unchecked, causing destructive grazing of kelp forests.
Process
Sea urchins eat kelp holdfasts. This can be caused by a lack of se ...
’) 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
Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...
,
isopods
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and ...
, kelp
crabs
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
, and
herbivorous
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 ...
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. 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, the ...
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 phytopla ...
from sewage, industrial byproducts and contaminants like
PCBs
Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...
and heavy metals (for example, copper, zinc), runoff of
organophosphates from agricultural areas, anti-fouling chemicals used in harbors and marinas (for example,
TBT and
creosote
Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics.
Some creosote types were ...
) and land-based pathogens like
fecal coliform bacteria
A fecal coliform (British: faecal coliform) is a facultatively anaerobic, rod-shaped, gram-negative, non-sporulating bacterium. Coliform bacteria generally originate in the intestines of warm-blooded animals. Fecal coliforms are capable of growt ...
.
*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 p ...
(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 of kelp-associated species such as
lobster and rockfish. Humans can also harvest kelp directly to feed aquaculture species such as
abalone and to extract the compound
alginic acid
Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colou ...
, 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; 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 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
![Melibe](https://upload.wikimedia.org/wikipedia/commons/5/5b/Melibe.2.jpg)
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,
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'') l ...
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
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 ...
(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
![Fish swarm through the kelp forest](https://upload.wikimedia.org/wikipedia/commons/d/dc/Fish_swarm_through_the_kelp_forest.jpg)
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 removal, both by scuba divers, and by
sea otters, 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 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