PHYTOPLANKTON Phytoplankton are microscopic plants that produce oxygen and organic matter from sunlight, carbon dioxide, and inorganic nutrients, like plants on land. Phytoplankton increase in abundance (or bloom) in the spring, and to a lesser extent, in the fall. Blooms can occur when the water column is stable, so phytoplankton can remain near the surface where light levels are high, and nutrients are available. Phytoplankton support many marine food webs as the key food source for zooplankton, that are in turn food for many fish and marine mammals. Phytoplankton abundance is an indicator of how productive a system is. Changes in the timing of the spring bloom can have consequences for many other organisms in the ecosystem. Through direct sampling and satellite imagery, scientists measure “chlorophyll a” in the surface ocean. Chlorophyll a is the main pigment used in photosynthesis. These measurements are used to represent the biomass and productivity of phytoplankton in the ocean. The more chlorophyll a that is detected, the more phytoplankton cells are assumed to be in the water (Figure 11). The magnitude, peak time, and duration of the blooms are assessed by looking at changes in the chlorophyll a concentrations (Figure 12a, b, c). This provides information on how the entire system changes from year to year. [See box: Crucial links between climate and marine productivity].
Magnified illustration of a coccolithophore which is a phytoplankton species. They have outer plates made of carbonate which can be vulnerable to the effects of ocean acidification. CANADA’S OCEANS NOW: ATLANTIC ECOSYSTEMS
2018
Microscopic images of phytoplankton. Credit: Fisheries and Oceans Canada.
Phytoplankton bloom off Newfoundland in 2002. Credit: NASA/GSFC, MODIS Land Rapid Response Team, Jacques Descloitres.
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