Mesh size effects on mesozooplankton community structure in a semi‐enclosed coastal area and surrounding sea ( S outh A driatic S ea)

Abstract This paper presents the results from a study in which two commonly used plankton mesh sizes (125 and 200 μm) were compared. We examined the influence of the mesh size effects on zooplankton community structure by comparing abundance, biomass and seasonal cycles of mesozooplankton. The study was performed at five stations (four in the marine lakes ‘Veliko jezero’ and ‘Malo jezero’, and one in the open sea in front of the lakes) during a 1‐year period (February 2008–February 2009). The estimated differences obtained from the catch results of the different mesh nets were more pronounced in semi‐enclosed coastal areas, such as lakes, than in the oligotrophic conditions prevailing at the station in the front of the lakes. Total zooplankton abundance with the 125‐μm net was significantly greater than with the 200‐μm net. The differences were mainly due to the loss of small‐sized copepods in the samples collected with the 200‐μm net. Excepting copepods, major losses were recorded for Limacina spp. and Bivalvia larvae. Abundance losses through the coarser net reflect the community structure and seasonal abundance pattern, which is most pronounced during the summer. Diversity indices and total dry weight were less influenced by mesh selection. The retention efficiency of the 125‐μm mesh size must be taken into account to provide a reliable description of the mesozooplankton community structure in coastal and especially eutrophicated areas. The 200‐μm mesh net could be recommended for oligotrophic systems due to the catch of larger calanoid species that contribute to overall zooplankton biomass, and because it allows a comparison with historical datasets.