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Marine Ecology Progress Series

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MEPS 239:11-29 (2002)  -  doi:10.3354/meps239011

Spatial and temporal variability of food web structure during the spring bloom in the Skagerrak

Marie Maar1,2,*, Torkel Gissel Nielsen1, Katherine Richardson2, Urania Christaki3, Ole Schou Hansen1, Sultana Zervoudaki3, Epaminondas D. Christou3

1Department of Marine Ecology, National Environmental Research Institute, PO Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark
2Department of Marine Ecology, University of Aarhus, Finlandsgade 14, 8200 Århus, Denmark
3National Centre for Marine Research, 16604 Hellenikon, Athens, Greece

ABSTRACT: During the intense spring diatom bloom, the spatial (km) and temporal (h) variability of the pelagic food web structure was investigated in the Skagerrak. Three surface water masses could be identified in the study area based on their temperature, salinity and biogeochemical characteristics. When the measured biological parameters were separated into water masses instead of stations, food web variability decreased by up to 41%. However, specific egg production rate by Acartia clausi and Oithona similis did not correlate with water masses and was probably influenced by other factors, e.g. small-scale turbulence. Bacterial production and Calanus-grazing followed a diurnal cycle with increased activity during the night. The grazing impact by the copepod community was assessed by the egg production and the gut fluorescence method. Despite the Calanus population, the copepod community only grazed <3% of daily primary production. The protozooplankton, however, ingested 2 to 4 times more of primary production than the copepods. Overall, the zooplankton community only grazed 17% of daily primary production, and consequently the majority of the spring bloom will leave the euphotic zone ungrazed as a potential food source for the benthos.

KEY WORDS: Spring bloom · Diurnal and spatial variability · Pelagic food web · Protozoans · Copepods

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