Kelp forest ecosystems_ biodiversity_ stability_ resilience and future

							       Kelp forest ecosystems: biodiversity, stability, resilience and future
ROBERT S. STENECK1, MICHAEL H. GRAHAM2, BRUCE J. BOURQUE3, DEBBIE CORBETT4, JON M. ERLANDSON5,
                                JAMES A. ESTES6, MIA J. TEGNER7†
1School of Marine Sciences, University of Maine, Walpole, ME 04573, U.S.A. (Steneck@maine.edu)
2Center for Population Biology, University of California, Davis, Davis, CA 95616, U.S.A. (mgraham@mlml.calstate.edu)
3Department of Anthropology, Bates College, Lewiston, ME 04240, U.S.A. (bbourque@abacus.bates.edu)
4US Fish and Wildlife Service, Anchorage, AK 99503-6119, U.S.A. (Debbie_Corbett@fws.gov)
5Department of Anthropology, University of Oregon, Eugene, OR 97403-1218, U.S.A. (jerland@oregon.uoregon.edu)
6U.S. Geological Survey, University of California, Santa Cruz, CA 95060 U.S.A. (jestes@cats.ucsc.edu)
7Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0201, U.S.A.
†Deceased.

Background                                                       the western North Atlantic. Globally urchin-induced
    Kelp forests dominate shallow rocky coasts of the            deforestation has been increasing over the past 2-3
world's cold-water marine habitats. They are comprised           decades. Continued fishing down of coastal foodwebs
of brown algae in the order Laminariales and include the         resulted in shifting harvesting targets from apex
largest organisms attached to the sea floor. Kelp forest         predators to their invertebrate prey including kelp-
ecosystems include structure-producing kelps and their           grazing herbivores. The recent global expansion of sea
myriad associated biota such as marine mammals, fishes,          urchin harvesting has led to the widespread extirpation of
crabs, sea urchins, mollusks, other algae and epibiota           this herbivore and in places kelp forests returned but, for
which collectively make this one of the most diverse and         the first time, these forests are devoid of vertebrate apex
productive ecosystems in the world. Economically, kelp           predators. In the western North Atlantic, large predatory
forest ecosystems have been significant to maritime              crabs have recently filled this void and they have become
peoples for thousands of years.                                  the new apex predator in this system. Similar shifts from
                                                                 fish to crab dominance may have occurred in coastal
Aims                                                             zones of the United Kingdom and Japan where large
    Past reviews rarely considered how kelp forest               predatory finfish were extirpated long ago.
ecosystems have changed at very large spatial scales
over very long periods of time (decades to millennia). A         Conclusion
longer historical perspective allows us to see how kelp              Over the past two centuries, commercial exploitation
forest ecosystems have changed and possibly where they           for export led to the extirpation of sea urchin predators
are headed in the future.                                        such as the sea otter in the North Pacific and predatory
                                                                 fishes such as cod in the North Atlantic. Thus it was not
Approach / Methods                                               until the large-scale removal of predators for export
    We review the conditions in which kelp forests               markets did sea urchin abundances increase and kelp
develop and where, why they become deforested.                   forests decline over vast areas. Despite southern
Through case studies from southern California, the               California having one of the longest known associations
Aleutian Islands and the western North Atlantic we               with coastal kelp forests, widespread deforestation is
examine the ecology of these well-studied locations,             rare. It is possible that functional redundancies among
which also represent the widest possible range in kelp           predators and herbivores make this most diverse system
forest biodiversity.                                             most stable. Such biodiverse kelp forests may also resist
                                                                 invasion from non-native species. In the species-
Results / Major findings                                         depauperate western North Atlantic, introduced algal
    Global     distribution    of    kelp    forests    are      competitors carpet the benthos and threaten future kelp
physiologically constrained by light at high latitudes and       dominance. There other non-native herbivores and
by nutrients, warm temperatures and other macrophytes            predators have become established and dominant
at low latitudes. Within mid-latitude belts (roughly 40-         components of this system.
60˚ latitude in both hemispheres) well-developed kelp
forests are most threatened by herbivory, usually from
sea urchins. For literally thousands of years overfishing
and extirpation of highly valued vertebrate apex
predators has triggered herbivore population increases,
leading to local kelp deforestation. Over the past century,
deforestation has become more wide-spread. This is most
profound and has the most long-lasting impacts on
species-depauperate systems such as those in Alaska and