engleski

Seasonal habitat utilization of Calanus helgolandicus in semi-enclosed marine lakes ("Veliko jezero", MPA "Mljet", South Adriatic Sea)

Calanus helgolandicus is a key pelagic copepod in trophic food webs of the North Atlantic and surrounding ecosystems. Changes in the population size of this species have rarely been investigated in the Adriatic Sea. In this work, we examine the seasonal habitat utilization of C. helgolandicus in regards to environmental variations and predation pressure in the Marine reserve of Mljet Lake “Veliko jezero”, a pristine ecosystem that offers a natural mesocosm to investigate ecology of zooplankton. In the marine lake “Veliko jezero”, C. helgolandicus is one of the dominant species reaching abundances up to 249, 6 ind/m3 and contributing up to 15, 86% of the total copepod abundance. We show that predation by jellyfish and chaetognaths act as major controls of the population size of C. helgolandicus. Pronounced seasonal vertical migration was observed. During the colder time of year, abundance is higher in upper layers. As temperature increase and upper layers become food depleted, C. helgolandicus migrate to concentrate in deeper layers, where they are faced with a trade-off between predatory risk and feeding opportunities. Such ecological interactions appear to be the main control on the population size of the species, although modifications in the functional responses might also occurs as consequence of food diet changes. Our results suggest large predator impact on zooplankton production in stratified marine environments.

Calanus helgolandicus; Marine Lakes; South Adriatic Sea; seasonal vertical migration

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