In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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1 Ecological Extinction and Evolution in the Brave New Ocean--JEREMY B. C. JACKSON
1 Ecological Extinction and Evolution in the Brave New Ocean--JEREMY B. C. JACKSON
Pages 5-26
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From page 5... ...
Today, the synergistic effects of human impacts are laying the groundwork for a comparably great Anthropocene mass extinction in the oceans with unknown ecological and evo lutionary consequences. Synergistic effects of habitat destruction, overfishing, introduced species, warming, acidification, toxins, and massive runoff of nutrients are transforming once complex ecosystems like coral reefs and kelp forests into monotonous level bottoms, transforming clear and productive coastal seas into anoxic dead zones, and transforming complex food webs topped by big animals into simplified, microbially dominated ecosystems with boom and bust cycles of toxic dinoflagellate blooms, jellyfish, and disease.
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From page 6... ...
. There is also considerable uncertainty about the relative importance and interactions among local perturbations, such as fishing and pollution, versus global changes in climate and ocean chemistry that operate over very different and noncongruent temporal and spatial scales (Hoegh-Guldberg et al., 2007; Knowlton and Jackson, 2008)
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From page 7... ...
The 16 original mammal species present before European contact were hunted to very low levels by 1900, with 3 extinct species including the sea mink Mustela macrodon, Atlantic walrus Odobenus rosmarus rosmarus, and possibly the coastal northwest Atlantic gray whale Eschrichtius robustus, as well as 7 more species that were severely reduced (Lötze and Milewski, 2004)
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From page 8... ...
. We examined ≈80 species or species groups that were assigned to six major taxonomic groups and seven ecological guilds.
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From page 9... ...
Fish 16–66 kg Pristine North Sea 99 Jennings and Blanchard (2004) Large predatory fish 1950s Global 90 Myers and Worm (2003)
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(2007) Coral reefs Live coral cover 1977 Caribbean 80 Newman et al.
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From page 11... ...
Among fish, diadromous salmon and sturgeon were depleted first, and then groundfish and large pelagics like tuna and sharks, and finally small pelagics like herring, menhaden, and sardines. Oysters were the first invertebrates to suffer extreme depletion, and the massive destruction of oyster reefs by dredging has permanently destroyed much of the formerly great habitat complexity of estuaries and coastal seas worldwide (Jackson et al., 2001; Kirby, 2004; Lötze et al., 2006)
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From page 12... ...
. For example, oysters were nearly eliminated by overfishing, but their recovery is now hampered by hypoxia due to eutrophication, by introduced species that compete for space and cause disease, and by the explosive rise of formerly uncommon predators that were previously kept in check by now overfished species (Lenihan and Peterson, 1998; Myers et al., 2007)
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From page 13... ...
, where removal of large groundfish resulted in large increases in pelagic shrimp and snow crabs, decreases in large zooplankton, and increases in phytoplankton. Thus, removal of top-down controls affects ecosystem structure and function of large marine ecosystems with complex food webs, as well as simpler, low-diversity systems.
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From page 14... ...
Finally, Jennings and Blanchard (2004) used the theoretical abundance– body mass relationship derived from macroecological theory to estimate the pristine biomass of fishes in the North Sea in comparison with the size and trophic structure of heavily exploited populations in 2001.
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Thus, trawling has drastically degraded most of the sea floor in these huge regions, and with multiple trawling episodes per year at favored sites, there is obviously no opportunity for ecosystem recovery. Eutrophication, Dead Zones, and the Rise of Slime Nutrient runoff is naturally greatest, and eutrophication, hypoxia, and toxic blooms are most intense, in estuaries and coastal seas like the Adriatic and Baltic seas and Chesapeake and San Francisco bays (Diaz, 2001; Jackson, 2001; Jackson et al., 2001; Lötze et al., 2006)
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From page 16... ...
THE OPEN OCEAN PELAGIC REALM Myers and Worm (2003) fired a shot heard around the world when they published their controversial assertion that 90% of all of the large (average approximately ≥50 kg)
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From page 17... ...
Nevertheless, Ward's and Myers's results clearly point toward the potential for strong trophic cascades and significant declines in mean trophic level as fishing erodes top-down control. Climate Change Warming and acidification of the pelagic realm due to the rise of CO2 comprise another uncontrolled experiment on a global scale (Feely et al., 2004)
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From page 18... ...
. CORAL REEFS Coral reefs are the most diverse marine ecosystems and among the most threatened (Knowlton, 2001; Hughes et al., 2003)
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. Most Caribbean coral communities in 1977 still resembled the first detailed descriptions from the 1950s (Goreau, 1959)
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. As for corals, the greatest fish biomass and largest fish occur on the uninhabited and protected atolls of the central and north central Pacific that may never have been severely degraded (Table 1.2)
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From page 21... ...
. As for oysters in estuaries, overfishing, increased macroalgal abundance, and degraded water quality act synergistically to decrease coral growth, recruitment, and survival.
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From page 22... ...
. This is the only good news I know of for coral reefs, and there is a pressing need to study these reefs to determine why corals have so far persisted in such abundance and the degree to which coral community composition is shifting toward more physiologically resilient species or to those with shorter generation times and faster growth.
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From page 23... ...
Ecological Extinction and Evolution in the Brave New Ocean / 23 TABLE 1.3 Status and Trends of Major Ocean Ecosystems Defined by Principal Symptoms and Drivers of Degradation in the >99% of the Global Ocean That Is Unprotected from Exploitation Coral reefs: Critically endangered Symptoms: Live coral reduced 50–93%; fish populations reduced 90%; apex predators virtually absent; other megafauna reduced by 90–100%; population explosions of seaweeds; loss of complex habitat; mass mortality of corals from disease and coral bleaching Drivers: Overfishing, warming and acidification due to increasing CO2, runoff of nutrients and toxins, invasive species Estuaries and coastal seas: Critically endangered Symptoms: Marshlands, mangroves, seagrasses, and oyster reefs reduced 67–91%; fish and other shellfish populations reduced 50–80%; eutrophication and hypoxia, sometimes of entire estuaries, with mass mortality of fishes and invertebrates; loss of native species; toxic algal blooms; outbreaks of disease; contamination and infection of fish and shellfish; human disease Drivers: Overfishing; runoff of nutrients and toxins; warming due to rise of CO2; invasive species; coastal land use Continental shelves: Endangered Symptoms: Loss of complex benthic habitat; fishes and sharks reduced 50–99%; eutrophication and hypoxia in "dead zones" near river mouths; toxic algal blooms; contamination and infection of fish and shellfish; decreased upwelling of nutrients; changes in plankton communities Drivers: Overfishing; trophic cascades; trawling; runoff of nutrients and toxins; warming and acidification due to rise of CO2; introduced species; escape of aquaculture species Open ocean pelagic: Threatened Symptoms: Targeted fishes reduced 50–90%; increase in nontargeted fish; increased stratification; changes in plankton communities Drivers: Overfishing; trophic cascades; warming and acidification due to rise of CO2 Coastal ecosystems are endangered to critically endangered on a global scale. The lesser endangerment of pelagic ecosystems reflects their remoteness from all factors except fishing and climate change, although there are no real baselines for comparison to critically evaluate changes in plankton communities.
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From page 24... ...
Failure to cap and reduce emissions of CO2 and other greenhouse gases will increase ocean temperatures and intensify acidification. Warmer and lighter surface waters will inhibit vertical mixing of the ocean, eventually leading to hypoxia or anoxia below the thermocline as in the Black Sea.
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From page 25... ...
Climate Change and Ocean Acidification The rise in greenhouse gases and the resulting global economic, social, and environmental consequences comprise the greatest challenge to humanity today. Moderation of consumption of fossil fuels in a time of rising global aspirations and finding alternative sources of energy will
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From page 26... ...
Most importantly, local conservation measures may help to buy time for marine ecosystems until we bring the rise of greenhouse gases under more effective control. ACKNOWLEDGMENTS I thank Julia Baum, Davy Kline, Nancy Knowlton, Loren McClenachan, Marah Newman, Forest Rohwer, Stuart Sandin, Enric Sala, Jennifer Smith, and Sheila Walsh for sharing their thoughts about the ecological degradation of the ocean and for many helpful suggestions.
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