Within Sea Patches we are studying how patches of plankton form in the ocean.

Currents continuously mix water and the minisculous plants and animals contained therein. But the distribution of plants and animals in the ocean is not at all uniform: the heterogeneous physical environment in combination with the biological tolerance of organisms yields major distribution patterns that follow climatic zones. On much smaller spatial scales many marine animals aggregate and form swarms, such that their distribution does not follow the distribution of different water masses.

Even plankton organisms of just about 2 mm size have been observed in large aggregations at surface. But it has been difficult to sample these small organisms on small scales, therefore the mechanisms of zooplankton patch formation in the ocean are poorly understood. It is therefore not known if biology plays a role in plankton aggregations at all, or if patches form purely based on physical factors. New developments in technology have made it possible to analyse plankton distributions on much smaller scales and in concert with physical factors. Many observations now point to an active part of organisms in forming patches, and recent research also indicates that even minisculous animals can maintain their position against currents.

We use modern technology (remote sensing, optical plankton counters) in combination with the latest marine physcial-biogeochemical models to

(1) locate patches

(2) to analayse zooplankton patch structure in detail and

(3) to describe the physical and biological mechanisms of zooplankton patch formation.

Our focus species is the small crustacean Calanus finmarchicus, which is very lipid-rich and a major food for many commercially harvested fishes. It is now also being harvested itself because of its richness in omega-3 fatty acids. A patchy distribution makes it challenging to correctly estimate its stock size. Our project will thus also contribute to a sustainable harvesting of a species at the bottom of the marine food web.