Editing Plankton (section)

==Biomass variability==
The growth of phytoplankton populations is dependent on light levels and nutrient availability. The chief factor limiting growth varies from region to region in the world's oceans. On a broad scale, growth of phytoplankton in the oligotrophic tropical and subtropical gyres is generally limited by nutrient supply, while light often limits phytoplankton growth in subarctic gyres. Environmental variability at multiple scales influences the nutrient and light available for phytoplankton, and as these organisms form the base of the marine food web, this variability in phytoplankton growth influences higher trophic levels. For example, at interannual scales phytoplankton levels temporarily plummet during [[El Niño]] periods, influencing populations of zooplankton, fishes, sea birds, and [[marine mammal]]s.

The effects of anthropogenic warming on the global population of phytoplankton is an area of active research. Changes in the vertical stratification of the water column, the rate of temperature-dependent biological reactions, and the atmospheric supply of nutrients are expected to have important impacts on future phytoplankton productivity.<ref>{{cite journal | last1 = Steinacher | first1 = M. | display-authors = etal | year = 2010 | title = Projected 21st century decrease in marine productivity: a multi-model analysis | journal = Biogeosciences | volume = 7 | issue = 3| pages = 979–1005 | doi = 10.5194/bg-7-979-2010 | bibcode = 2010BGeo....7..979S | doi-access = free | hdl = 11858/00-001M-0000-0011-F69E-5 | hdl-access = free }}</ref> Additionally, changes in the mortality of phytoplankton due to rates of zooplankton grazing may be significant.

[[File:Cycling of marine phytoplankton.png|thumb|upright=1.8|left| {{center|Marine phytoplankton cycling throughout water column}}]]
[[File:Amphipodredkils.jpg|thumb|upright=1.2| [[Amphipoda|Amphipod]] with curved [[exoskeleton]] and two long and two short antennae]]
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