54 Marine Ecosystems nitrogenous fertilizers and the mining of phosphate rock have generated increased concern about the effects of eutrophication on enclosed marine ecosystems (Nixon, 1995) Eutrophic ecosystems have algal production in excess of 300 g C mÀ2 yrÀ1, which results in areas of anoxia and loss of habitat for fish and other organisms Relatively high rates of denitrification on continental shelves remove excess nitrogen originating from land sources and, in concert with dilution, help prevent adverse eutrophication effects in open coastal areas (Soetaert and Middelburg, 2009) Overfishing Globally, about 30% of commercial fish stocks are over-fished and another 44% are being fished at or near the maximum potential long-term catch rate Atlantic halibut, cod, orange roughly, and many species of salmon are now severely depleted Significant changes in community structure as a result of overfishing have occurred in ecosystem structure in the Bering, Barents, and Baltic Seas (National Academy of Sciences, Committee on Ecosystem Management for Sustainable Marine Fisheries, 1999) Bottom-fishing has been shown to result in physical destruction of some bottom habitats Efforts to reverse the effects of over-fishing and habitat destruction may be having some positive effects in certain ecosystems (Worm et al., 2009) Overfishing has resulted in major changes in coral reef ecosystems Normally, herbivorous fish heavily graze the attached algae, ensuring enough open reef surface for corals to settle and grow This is especially true following major storms when wave action reduces coral coverage and circumstances are favorable for rapid algal growth In the Caribbean, under normal circumstances, sea urchin grazing may compensate for reductions in fish grazing A combination of overfishing and the decimation of sea urchin grazers by disease favored algal growth following a hurricane, which resulted in reefs dominated by algae (National Academy of Sciences, 1995) Recent research on coral-algal competition, in combination with the effects of no-take marine protected areas, have provided many insights into the positive and negative interactions among members of coral reef food webs (Hughes et al., 2007; McCook et al., 2010) Invasive Species Unwanted, non-indigenous species are often introduced to new geographic regions, both deliberately to start new fisheries and accidentally through release from aquaria or ballast water carried by ships, sometimes with disastrous consequences The Asian clam became established in the San Francisco Bay in 1986 and quickly displaced other species from large areas of the seabed and altered the water chemistry of the bay (National Academy of Sciences, 1995) The introduction of predatory green crabs to coastal environments on the east coast resulted in major reductions in shellfish beds and the green crab has become invasive in many other areas In short, invasive species have become a significant problem in many marine coastal environments and considerable effort is needed to curb this severe problem (Ruiz et al., 2000) In summary, the oceans encompass a broad array of habitats that differ in their diversity, function, and vulnerability Much of the vast area of the oceans is poorly described, but we have some understanding of a variety of globally essential ecosystem processes and predictors of biodiversity (Tittensor et al., 2010) Species loss may threaten not only the organisms themselves but also the many ecological processes that serve the rest of the planet and its human populations See also: Coastal Beach Ecosystems Corals and Coral Reefs Endangered Marine Invertebrates Estuarine Ecosystems Human Impact on Biodiversity, Overview Intertidal Ecosystems Invertebrates, Marine, Overview Mangrove Ecosystems Pelagic Ecosystems Vents References Alongi DM (1998) Coastal Ecosystem Processes Boca Raton: CRC Press Andersen RA, Bidigare RR, Keller MD, and Latasa M (1996) A comparison of HPLC pigment signatures and electronic microscopic observations for oligotrophic waters of the North Atlantic and Pacific Oceans Deep-Sea Research II 43: 517–537 Baco A and Smith C (2003) High species richness in deep-sea chemoautotrophic whale skeleton communities Marine Ecological Progress Series 260: 109–114 Behrenfeld MJ, O’Malley RT, Siegel DA, et al (2006) Climate-driven trends in contemporary ocean productivity Nature 444: 752–755 Braeckman U, Provoost P, Gribsholt B, Van Gansbeke D, and Middelburg (2010) Role of macrofauna functional traits and density in biogeochemical fluxes and bioturbation Marine Ecological Progress Series 399: 173–186 Briggs JC (1974) Marine Zoogeography New York: McGraw Hill Cohen JE (1994) Marine and continental food webs: Three paradoxes? Philosophical Transactions of Royal Society of London B 343: 57–69 Dayton PK, Tegner MJ, Edwards PB, and Riser KL (1999) Temporal and spatial scales of kelp demography: The role of oceanographic climate Ecological Monographs 69: 219–250 DeSalle R, Egan MG, and Siddall M (2005) The unholy trinity: Taxonomy, species delimitation and DNA barcoding Philosophical Transactions of Royal Society of London B 360: 1905–1916 Falkowski PG, Barber RT, and Smetacek V (1998) Biogeochemical controls and feedbacks on ocean primary production Science 281: 200–206 FAO (2007) Report on the FAO Workshop on Vulnerable Ecosystems and Destructive Fishing in Deep-Sea Fisheries FAO Fisheries Report No 829, Rome, 26–29 June 2007 Field CB, Behrenfeld MJ, Randerson JT, and Falkowski P (1998) Primary production of the biosphere: Integrating terrestrial and oceanic components Science 281: 237–240 Gage J and Tyler PA (1991) Deep-Sea Biology: A Natural History of Organisms at the Deep-Sea Floor Cambridge: Cambridge University Press Grassle JF (1986) The ecology of deep-sea hydrothermal vent communities Advances in Marine Biology 23: 443–452 Grassle JF and Maciolek NJ (1992) Deep-sea species richness: Regional and local diversity estimates from quantitative bottom samples American Naturalist 139: 313–341 Hughes TP, Rodrigues MJ, Bellwood DR, et al (2007) Phase shifts, herbivory, and the resilience of coral reefs to climate change Current Biology 17: 360–365 Karl DM (1999) A sea of change: Biogeochemical variability in the North Pacific Subtopical Gyre Ecosystems 2: 181–214 Lambshead PJD, Elge BM, Thistle E, Eckman JE, and Barnett PRO (1994) A comparison of the biodiversity of deep-sea marine nematodes from three stations in the Rockall Trough, Northeast Atlantic, and one station in the San Diego Trough, Northeast Pacific Biodiversity Research 2(95): 107 Longhurst A (1998) Ecological Geography of the Sea San Diego, CA: Academic Press May RM and Godfrey J (1994) Biological diversity: Differences between land and sea Philosophical Transactions of Royal Society of London Series B 343: 105–111 McCook LJ, Ayling T, Cappo M, et al (2010) Adaptive management of the Great Barrier Reef: A globally significant demonstration of the benefits of networks of marine reserves Proceedings of the National Academy of Sciences 107: 18278–18285