Editing Kelp forest (section)

== Trophic ecology ==
[[File:Seaurchin 300.jpg|thumb|right|Sea urchins like this [[Strongylocentrotus purpuratus|purple sea urchin]] can damage kelp forests by chewing through kelp [[holdfast (biology)|holdfast]]s]]
[[File:Mother sea otter with rare twin baby pups (9137174915).jpg|thumb|right|The [[sea otter]] is an important predator of [[sea urchin]]s]]
[[File:Calliostoma annulatum.jpg|thumb|right|The jeweled top snail ''[[Calliostoma annulatum]]'' grazing on a blade of giant kelp]]
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.<ref>{{Cite journal |last=Jackson |first=George A. |date=November 1977 |title=Nutrients and production of giant kelp, Macrocystis pyrifera, off southern California1 |url=https://aslopubs.onlinelibrary.wiley.com/doi/10.4319/lo.1977.22.6.0979 |journal=Limnology and Oceanography |language=en |volume=22 |issue=6 |pages=979–995 |doi=10.4319/lo.1977.22.6.0979 |bibcode=1977LimOc..22..979J |issn=0024-3590 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007145632/https://aslopubs.onlinelibrary.wiley.com/doi/10.4319/lo.1977.22.6.0979 |url-status=live |url-access=subscription }}</ref><ref name="Dayton1999">{{Cite journal |last1=Dayton |first1=Paul K. |last2=Tegner |first2=Mia J. |last3=Edwards |first3=Peter B. |last4=Riser |first4=Kristin L. |date=May 1999 |title=Temporal and Spatial Scales of Kelp Demography: The Role of Oceanographic Climate |url=http://www.jstor.org/stable/2657238 |journal=Ecological Monographs |volume=69 |issue=2 |pages=219 |doi=10.2307/2657238|jstor=2657238 |url-access=subscription }}</ref> This allows kelp to grow and subsequently support herbivores, which in turn support consumers at higher [[trophic level]]s.<ref name="Carr">{{Cite journal |last=Carr |first=Mark H. |date=July 1994 |title=Effects of Macroalgal Dynamics on Recruitment of a Temperate Reef Fish |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1937457 |journal=Ecology |language=en |volume=75 |issue=5 |pages=1320–1333 |doi=10.2307/1937457 |jstor=1937457 |bibcode=1994Ecol...75.1320C |issn=0012-9658 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151821/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1937457 |url-status=live |url-access=subscription }}</ref> 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,<ref name="Estes1995">{{Cite journal |last1=Estes |first1=James A. |last2=Duggins |first2=David O. |date=February 1995 |title=Sea Otters and Kelp Forests in Alaska: Generality and Variation in a Community Ecological Paradigm |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937159 |journal=Ecological Monographs |language=en |volume=65 |issue=1 |pages=75–100 |doi=10.2307/2937159 |jstor=2937159 |bibcode=1995EcoM...65...75E |issn=0012-9615 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151822/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937159 |url-status=live |url-access=subscription }}</ref> [[sea otters]] (''Enhydra lutris'') control populations of herbivorous [[sea urchins]] 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]]. 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.<ref name="Graham2004" /> However, the removal of multiple predators can effectively release urchins from predator pressure and allow the system to follow trajectories towards kelp forest degradation.<ref name="Pearse&Hines">{{Cite journal |last1=Pearse |first1=J. S. |last2=Hines |first2=A. H. |date=March 1979 |title=Expansion of a central California kelp forest following the mass mortality of sea urchins |url=http://link.springer.com/10.1007/BF00389034 |journal=Marine Biology |language=en |volume=51 |issue=1 |pages=83–91 |doi=10.1007/BF00389034 |bibcode=1979MarBi..51...83P |issn=0025-3162 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151827/https://link.springer.com/article/10.1007/BF00389034 |url-status=live |url-access=subscription }}</ref> Similar examples exist in [[Nova Scotia]],<ref>{{Cite journal |last1=Scheibling |first1=Re |last2=Hennigar |first2=Aw |date=1997 |title=Recurrent outbreaks of disease in sea urchins Strongylocentrotus droebachiensis in Nova Scotia:evidence for a link with large-scale meteorologic and oceanographic events |url=http://www.int-res.com/abstracts/meps/v152/p155-165/ |journal=Marine Ecology Progress Series |language=en |volume=152 |pages=155–165 |doi=10.3354/meps152155 |bibcode=1997MEPS..152..155S |issn=0171-8630 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151829/https://www.int-res.com/abstracts/meps/v152/p155-165/ |url-status=live }}</ref> South Africa,<ref>{{Cite journal |last1=Velimirov |first1=B. |last2=Field |first2=J. G. |last3=Griffiths |first3=C. L. |last4=Zoutendyk |first4=P. |date=August 1977 |title=The ecology of kelp bed communities in the Benguela upwelling system: Analysis of biomass and spatial distribution |url=https://link.springer.com/10.1007/BF02207857 |journal=Helgoländer Wissenschaftliche Meeresuntersuchungen |language=en |volume=30 |issue=1–4 |pages=495–518 |doi=10.1007/BF02207857 |issn=0017-9957 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151830/https://link.springer.com/article/10.1007/BF02207857 |url-status=live }}</ref> Australia,<ref>{{Cite journal |last=Andrew |first=N. L. |date=March 1993 |title=Spatial Heterogeneity, Sea Urchin Grazing, and Habitat Structure on Reefs in Temperate Australia |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1939293 |journal=Ecology |language=en |volume=74 |issue=2 |pages=292–302 |doi=10.2307/1939293 |jstor=1939293 |bibcode=1993Ecol...74..292A |issn=0012-9658 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007151959/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1939293 |url-status=live |url-access=subscription }}</ref> and Chile.<ref>{{Cite journal |last=Dayton |first=Paul K. |date=December 1985 |title=The Structure and Regulation of Some South American Kelp Communities |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937131 |journal=Ecological Monographs |language=en |volume=55 |issue=4 |pages=447–468 |doi=10.2307/2937131 |jstor=2937131 |bibcode=1985EcoM...55..447D |issn=0012-9615 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152504/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937131 |url-status=live |url-access=subscription }}</ref> 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.<ref name="Sala&Graham">{{Cite journal |last1=E |first1=Sala |last2=Mh |first2=Graham |date=2002-03-19 |title=Community-wide distribution of predator-prey interaction strength in kelp forests |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=99 |issue=6 |pages=3678–3683 |doi=10.1073/pnas.052028499 |doi-access=free |issn=0027-8424 |pmid=11891292|pmc=122583 |bibcode=2002PNAS...99.3678S }}</ref><ref>{{Cite journal |last1=Byrnes |first1=Jarrett |last2=Stachowicz |first2=John J. |last3=Hultgren |first3=Kristin M. |last4=Randall Hughes |first4=A. |last5=Olyarnik |first5=Suzanne V. |last6=Thornber |first6=Carol S. |date=January 2006 |title=Predator diversity strengthens trophic cascades in kelp forests by modifying herbivore behaviour |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2005.00842.x |journal=Ecology Letters |language=en |volume=9 |issue=1 |pages=61–71 |doi=10.1111/j.1461-0248.2005.00842.x |pmid=16958869 |bibcode=2006EcolL...9...61B |issn=1461-023X |access-date=2024-10-06 |archive-date=2022-07-29 |archive-url=https://web.archive.org/web/20220729082928/https://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2005.00842.x |url-status=live |url-access=subscription }}</ref><ref name="Halpern2006">{{Cite journal |last1=Halpern |first1=Benjamin S. |last2=Cottenie |first2=Karl |last3=Broitman |first3=Bernardo R. |date=2006-05-26 |title=Strong top-down control in southern California kelp forest ecosystems |url=https://pubmed.ncbi.nlm.nih.gov/16728644/ |journal=Science |volume=312 |issue=5777 |pages=1230–1232 |doi=10.1126/science.1128613 |issn=1095-9203 |pmid=16728644 |bibcode=2006Sci...312.1230H |access-date=2024-10-06 |archive-date=2024-06-30 |archive-url=https://web.archive.org/web/20240630184439/https://pubmed.ncbi.nlm.nih.gov/16728644/ |url-status=live }}</ref>

The transition from macroalgal (i.e. kelp forest) to denuded landscapes dominated by sea urchins (or ‘[[urchin barrens]]’) is a widespread phenomenon,<ref name="Steneck 2002" /><ref>Lawrence, J.M. 1975. On the relationships between marine plants and sea urchins. Oceanography and Marine Biology, An Annual Review. 13: 213–286.</ref><ref>{{Cite journal |last=Hughes |first=T. P. |date=1994-09-09 |title=Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral reef |url=https://pubmed.ncbi.nlm.nih.gov/17801530/ |journal=Science |volume=265 |issue=5178 |pages=1547–1551 |doi=10.1126/science.265.5178.1547 |issn=0036-8075 |pmid=17801530 |bibcode=1994Sci...265.1547H |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152338/https://pubmed.ncbi.nlm.nih.gov/17801530/ |url-status=live }}</ref><ref>{{Cite journal |last=Sivertsen |first=Knut |date=2006-11-27 |title=Overgrazing of Kelp Beds Along the Coast of Norway |url=http://link.springer.com/10.1007/s10811-006-9064-4 |journal=Journal of Applied Phycology |language=en |volume=18 |issue=3–5 |pages=599–610 |doi=10.1007/s10811-006-9064-4 |bibcode=2006JAPco..18..599S |issn=0921-8971 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152341/https://link.springer.com/article/10.1007/s10811-006-9064-4 |url-status=live |url-access=subscription }}</ref><ref>{{Cite journal |last1=Filbee-Dexter |first1=Karen |last2=Scheibling |first2=Robert E. |date=January 2017 |title=The present is the key to the past: linking regime shifts in kelp beds to the distribution of deep-living sea urchins |url=https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.1638 |journal=Ecology |volume=98 |issue=1 |pages=253–264 |doi=10.1002/ecy.1638 |pmid=28052391 |bibcode=2017Ecol...98..253F |issn=0012-9658 |access-date=2024-03-31 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152336/https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.1638 |url-status=live |url-access=subscription }}</ref> often resulting from trophic cascades like those described above; the two phases are regarded as alternative stable states of the ecosystem.<ref name="Dayton1992">{{Cite journal |last1=Dayton |first1=Paul K. |last2=Tegner |first2=Mia J. |last3=Parnell |first3=Paul E. |last4=Edwards |first4=Peter B. |date=September 1992 |title=Temporal and Spatial Patterns of Disturbance and Recovery in a Kelp Forest Community |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937118 |journal=Ecological Monographs |language=en |volume=62 |issue=3 |pages=421–445 |doi=10.2307/2937118 |jstor=2937118 |bibcode=1992EcoM...62..421D |issn=0012-9615 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152337/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937118 |url-status=live |url-access=subscription }}</ref><ref>{{Cite journal |last=Pearse |first=John S. |date=2006-11-10 |title=Ecological role of purple sea urchins |url=https://pubmed.ncbi.nlm.nih.gov/17095690/ |journal=Science |volume=314 |issue=5801 |pages=940–941 |doi=10.1126/science.1131888 |issn=1095-9203 |pmid=17095690 |bibcode=2006Sci...314..940P |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152410/https://pubmed.ncbi.nlm.nih.gov/17095690/ |url-status=live }}</ref><ref>{{Cite journal |last1=Filbee-Dexter |first1=Karen |last2=Scheibling |first2=Robert E. |date=2014-01-09 |title=Sea urchin barrens as alternative stable states of collapsed kelp ecosystems |url=https://www.int-res.com/abstracts/meps/v495/p1-25/ |journal=Marine Ecology Progress Series |volume=495 |pages=1–25 |doi=10.3354/meps10573 |bibcode=2014MEPS..495....1F |issn=0171-8630 |access-date=2024-03-31 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152342/https://www.int-res.com/abstracts/meps/v495/p1-25/ |url-status=live }}</ref> The recovery of kelp forests from barren states has been documented following dramatic perturbations, such as urchin disease or large shifts in thermal conditions.<ref name="Pearse&Hines" /><ref>{{Cite journal |last=Lafferty |first=Kevin D. |date=October 2004 |title=Fishing for lobsters indirectly increases epidemics in sea urchins |url=https://esajournals.onlinelibrary.wiley.com/doi/10.1890/03-5088 |journal=Ecological Applications |language=en |volume=14 |issue=5 |pages=1566–1573 |doi=10.1890/03-5088 |bibcode=2004EcoAp..14.1566L |issn=1051-0761 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152421/https://esajournals.onlinelibrary.wiley.com/doi/10.1890/03-5088 |url-status=live }}</ref><ref name="Vasquez">{{Cite journal |last1=Vásquez |first1=Julio A. |last2=Vega |first2=J. M. Alonso |last3=Buschmann |first3=Alejandro H. |date=2006-11-27 |title=Long Term Variability in the Structure of Kelp Communities in Northern Chile and the 1997–98 ENSO |url=http://link.springer.com/10.1007/s10811-006-9056-4 |journal=Journal of Applied Phycology |language=en |volume=18 |issue=3–5 |pages=505–519 |doi=10.1007/s10811-006-9056-4 |bibcode=2006JAPco..18..505V |issn=0921-8971 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152610/https://link.springer.com/article/10.1007/s10811-006-9056-4 |url-status=live |url-access=subscription }}</ref> 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 [[starfish|seastars]], [[isopods]], kelp [[crabs]], and [[herbivorous]] fishes.<ref name="Dayton 1985a" /><ref name="Sala&Graham" /> 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 thalli; when drift subsidies are unavailable, grazers directly impact the physical structure of the ecosystem.<ref>{{Cite journal |last=Cowen |first=Robert K. |date=May 1983 |title=The effects of sheephead (Semicossyphus pulcher) predation on red sea urchin (Strongylocentrotus franciscanus) populations: an experimental analysis |url=http://link.springer.com/10.1007/BF00399225 |journal=Oecologia |language=en |volume=58 |issue=2 |pages=249–255 |doi=10.1007/BF00399225 |pmid=28310586 |bibcode=1983Oecol..58..249C |issn=0029-8549 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152611/https://link.springer.com/article/10.1007/BF00399225 |url-status=live |url-access=subscription }}</ref><ref name="Ebeling">{{Cite journal |last1=Ebeling |first1=A. W. |last2=Laur |first2=D. R. |last3=Rowley |first3=R. J. |date=January 1985 |title=Severe storm disturbances and reversal of community structure in a southern California kelp forest |url=http://link.springer.com/10.1007/BF00392498 |journal=Marine Biology |language=en |volume=84 |issue=3 |pages=287–294 |doi=10.1007/BF00392498 |bibcode=1985MarBi..84..287E |issn=0025-3162 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152905/https://link.springer.com/article/10.1007/BF00392498 |url-status=live |url-access=subscription }}</ref> Many studies in Southern California have demonstrated that the availability of drift kelp specifically influences the foraging behavior of sea urchins.<ref name="Dayton 1984">{{Cite journal |last1=Dayton |first1=Paul K. |last2=Tegner |first2=Mia J. |date=1984-04-20 |title=Catastrophic Storms, El Niño, and Patch Stability in a Southern California Kelp Community |url=https://www.science.org/doi/10.1126/science.224.4646.283 |journal=Science |language=en |volume=224 |issue=4646 |pages=283–285 |doi=10.1126/science.224.4646.283 |issn=0036-8075 |pmid=17734914 |bibcode=1984Sci...224..283D |access-date=2024-10-06 |archive-date=2023-02-28 |archive-url=https://web.archive.org/web/20230228164738/https://www.science.org/doi/10.1126/science.224.4646.283 |url-status=live |url-access=subscription }}</ref><ref>{{Cite journal |last1=Harrold |first1=Christopher |last2=Reed |first2=Daniel C. |date=August 1985 |title=Food Availability, Sea Urchin Grazing, and Kelp Forest Community Structure |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1939168 |journal=Ecology |language=en |volume=66 |issue=4 |pages=1160–1169 |doi=10.2307/1939168 |jstor=1939168 |bibcode=1985Ecol...66.1160H |issn=0012-9658 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152907/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1939168 |url-status=live |url-access=subscription }}</ref> Drift kelp and kelp-derived particulate matter have also been important in subsidizing adjacent habitats, such as sandy beaches and the rocky intertidal.<ref>{{Cite journal |last1=Koop |first1=K |last2=Newell |first2=Rc |last3=Lucas |first3=Mi |date=1982 |title=Biodegradation and Carbon Flow Based on Kelp (Ecklonia maxima) Debris in a Sandy Beach Microcosm |url=http://www.int-res.com/articles/meps/7/m007p315.pdf |journal=Marine Ecology Progress Series |language=en |volume=7 |pages=315–326 |doi=10.3354/meps007315 |bibcode=1982MEPS....7..315K |issn=0171-8630 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152850/http://www.int-res.com/articles/meps/7/m007p315.pdf |url-status=live }}</ref><ref>{{Cite journal |last1=Bustamante |first1=R. 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M. |last3=Eekhout |first3=S. |date=October 1995 |title=Maintenance of an Exceptional Intertidal Grazer Biomass in South Africa: Subsidy by Subtidal Kelps |url=https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1941704 |journal=Ecology |language=en |volume=76 |issue=7 |pages=2314–2329 |doi=10.2307/1941704 |jstor=1941704 |bibcode=1995Ecol...76.2314B |issn=0012-9658 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152908/https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1941704 |url-status=live |url-access=subscription }}</ref><ref>{{Cite journal |last1=Kaehler |first1=S |last2=Pakhomov |first2=Ea |last3=Kalin |first3=Rm |last4=Davis |first4=S |date=2006-07-03 |title=Trophic importance of kelp-derived suspended particulate matter in a through-flow sub-Antarctic system |url=http://www.int-res.com/abstracts/meps/v316/p17-22/ |journal=Marine Ecology Progress Series |language=en |volume=316 |pages=17–22 |doi=10.3354/meps316017 |bibcode=2006MEPS..316...17K |issn=0171-8630 |access-date=2024-10-06 |archive-date=2024-10-07 |archive-url=https://web.archive.org/web/20241007152912/https://www.int-res.com/abstracts/meps/v316/p17-22/ |url-status=live }}</ref>