Turbulence and zooplankton production: insights from PROVESS

Zooplankton are directly influenced by turbulence in both a passive and an active manner. Passively, zooplankton are at the mercy of turbulence in how it affects their vertical mixing, encounter rate, detection abilities and feeding current efficiency. Many zooplankton species, however, are actively able to mitigate the effects of turbulence by modifying their behaviour, e.g. vertical migration, prey switching and habituation to hydromechanical stimuli. Both theoretical treatments of these processes and field observations from the northern North Sea are examined. Field observations show that some copepod species actively migrate to avoid high turbulence levels in surface waters. Furthermore, observations show a negative relationship between turbulence and zooplankton ingestion rates. This supports the paradigm of a dome-shaped response for zooplankton production with environmental turbulence. A theoretical treatment shows that the reaction distance, R, for an ambush-feeding copepod feeding on swimming organisms follows R ∝ ε−1/6 where ε is the turbulent dissipation rate, a result that shows close agreement with previously reported experimental results.