the physical controls on phytoplankton in shelf seas

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overview

Shelf seas are ideal places to explore how phytoplankton are affected by the physical environment because different conditions, such as mixed and stratified water columns, occur relatively close together. Conditions also change rapidly due to physical processes including internal waves and tides. Studying how these processes impact the phytoplankton require biologists and physicists to work closely together. 

what controls phytoplankton species distributions?

Phytoplankton species occurred at different depths in the water column, even within the narrow seasonal thermocline. The taxonomic gradients can be explained by light and nutrient availability at different depths. In particular, phytoplankton occurred at depths where their pigments are well suited to the light spectrum.

how much primary production occurs in the thermocline?

Despite the low light conditions, phytoplankton in the seasonal thermocline carry out as much photosynthesis as those in the surface mixed layer and about half as much seasonal 'new' production as the spring bloom. The thermocline is thus an important location of primary production in shelf seas but it cannot be seen from the surface or by satellites.

why do larger species occur at the shelf edge?

We found larger phytoplankton species at the shelf edge compared to either on or off the shelf. The larger phytoplankton depend on the nutrients supplied to the surface by mixing associated with the internal tide on spring - neap tidal cycles. The larger celled phytoplankton could be important for sustaining fisheries in the region.

how do phytoplankton cope with low light?

Phytoplankton acclimate to the low light conditions in the thermocline by increasing the number, rather than size, of the reaction centres used in photosynthesis.