Publication Abstract

Structure of zooplankton communities at three contrasting sites in the North Sea.

Structure of zooplankton communities at three contrasting sites in the North Sea.

Painting, S.J.*, Kürten, B., Baars, M., Oosterhuis, S.

Zooplankton community structure was examined at 3 ecohydrodynamically distinct sites in the North Sea: in the southern Bight (SB), at the Oyster Grounds (OG) and north of the Dogger Bank (ND). Cruises took place in winter, spring and autumn 2007. Samples were collected using vertically hauled ring-nets with different mesh sizes: 50µm, 200µm, 270µm and 500µm. Preserved samples were split: (1) to estimate crustacean biomass using a chitin assay (Harris et al. 2000), and (2) for microscope analysis. Larger copepods were counted by species and developmental stage; most other taxa were identified to genus. Species were assigned to broad functional groups: calanoid, cyclopoid and harpacticoid. Calanoid copepods were categorised as large or small calanoids. Large calanoids included the adults and juveniles of species of Calanus, Metridia, Euchaeta, Labidocera and Anomalocera. Small calanoids included the adults and juveniles of species of Acartia, Candacea, Centropages, Isias, Microcalanus, Paracalanus, Pseudocalanus and Temora.

Estimates of biomass were highest (2.5 g C m^-2) at the ND site in May. Similar results were obtained from the 200µm, 270µm and 500µm nets. At the SB and OG sites, relatively high biomass values were obtained from the 50µm net samples. Average biomass ratios (50:200µm nets) showed that biomass in the smaller size fraction was approximately 4 times higher than in the ≥ 200µm fraction at the SB and 2 times higher at the OG. In terms of abundances, copepods dominated the zooplankton community at all sites. Small calanoids dominated the 200µm net samples at all sites during all cruises (up to 1.2 x 10⁵ individuals m^-2), except at the ND site in April. At the ND, large calanoid copepods contributed 50 % of total copepod numbers in April (up to 1.5 x 10⁵ individuals m^-2), approximately 1 month after the spring phytoplankton bloom. Results of this study show that small calanoids are an important component of the zooplankton community at the 3 study sites in the North Sea, including the site north of the Dogger Bank. Also, that the use of large-mesh-sized nets (≥ 270µm) may result in underestimates of crustacean biomass and copepod abundance.

Painting, S.J.*, Kürten, B., Baars, M., Oosterhuis, S.

ICES/CIESM Workshop to compare Zooplankton Ecology and Methodologies between the Mediterranean and the North Atlantic, October 2008, Hellenic Centre for Marine Research, Heraklion, Greece.