Global Change
Therefore, Alterations to global oceanography could lead to changes in species composition and biomass in these communities (Gitay et al. 2002; Hays et al. 2005; Bjork et al. 2008) and affect all levels of marine food webs.
The warmer, fresher surface water associated with a warming planet leads to stratification (Schmittner 2005; Jackson 2008) that can trap valuable nutrients in the deep ocean, thus separating them from the well-lit upper ocean where phytoplankton can transfer them into energy and make them available to higher levels in the food web. This phenomenon has implications for some of the most productive parts of Earth’s oceans, where upwelling of deep waters and nutrients supports massively abundant surface ecosystems. If suppression of upwelling occurs to any degree, fisheries, and the people and wildlife that rely on them will certainly be negatively affected (Cheung et al. 2008).
In addition to changes in community composition and productivity in ocean ecosystems, warming temperatures will undoubtedly change the geographical ranges of marine species. Species are already migrating and occurring at higher latitudes than before (Perry et al. 2005) though not always at predictable rates (Perry et al.2009).
As the tropics warm, it is unclear if these species will be able to adapt or if they will only be able to migrate, but recent research implies that heat tolerant species are already near the physiological limit of their temperature range (Tewksbury et al. 2008). Therefore, as they migrate poleward, there might not be populations or species available to replace them, nor suitable or sufficient prey species in their new locations.
Dangerous invasive species, that cause disease and broad scale environmental destruction, can also migrate and are often more successful in weak, altered systems (Lotze et al. 2006). As these species move into other ecosystems, they can cause serious harm (Mooney and Cleland 2001) even before direct impacts of climate change are observable.
In addition to the effects associated with warming, marine ecosystems are expected to show drastic changes associated with ocean acidification within the next 50 years. Ocean acidification decreases the ability of many marine organisms to build their shells and skeletal structures and affects reproduction, behavior, and general physiological functions of some others (Orr et al. 2009).
Several important planktonic primary producers rely on calcium carbonate to form protective shells. Under acidic conditions, calcium carbonate dissolves and these organisms are put at risk. Because these producers constitute the bottom of the food web, this risk can be expected to resonate throughout marine ecosystems, including important commercial fisheries and the communities who rely on them.
