MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12512

Trophic decoupling of mesozooplankton production and pelagic planktivores sprat (Sprattus sprattus) and herring (Clupea harengus) in the Central Baltic Sea

Matthias Bernreuther*, Janna Peters, Christian Möllmann, Jasmin Renz, Jörg Dutz, Jens-Peter Herrmann, Axel Temming

*Email: matthias.bernreuther@thuenen.de

ABSTRACT: A quantitative analysis of the predation impact of planktivores on zooplankton is essential for a proper understanding of energy flow and trophic coupling in ecosystems. For a quantification of the trophic dynamics between zooplankton and small pelagic fish in the Baltic Sea, we conducted a temporally resolved investigation on the diet, feeding and predation impact of the two dominant planktivorous fish species, sprat (Sprattus sprattus L.) and herring (Clupea harengus L.) in the Central Baltic Sea (Bornholm Basin, BB). A bi-weekly to monthly coverage of the BB between April 2002 and November 2003 included net sampling of copepods, determination of the predator stock size using combined hydroacoustics and trawl surveys, and an extensive stomach content sampling programme. Herring and sprat were mainly zooplanktivorous, largely feeding on the calanoid copepods Temora longicornis, Pseudocalanus acuspes and Acartia spp. and additionally on the cladocerans Bosmina spp. and Podon spp. in summer. We observed a temporally high predation impact of mainly sprat and herring on T. longicornis and P. acuspes in April and May, when considerably more than the production of these two copepod species (copepodite stages C1-6) was consumed (consumption/production (C/P) > 3.5). However, the impact on the population dynamics of both copepods in the BB was negligible. Likewise, the impact on Acartia spp. was considered negligible (C/P < 0.1). If integrated over the year, the utilization of the estimated copepod production by both clupeids was comparatively low with only 18% of the annual production of T. longicornis. 36% of the annual production of P. acuspes was consumed by both clupeids together, while the production of Acartia species (1.4%) and cladocerans (2.3%) was almost completely unused by fish predators. The utilization of only 9% of the combined production of copepods and cladocerans indicates an overall poor trophic coupling between mesozooplankton and pelagic planktivores in the Central Baltic Sea.