Individual biovolume of some dominant copepod species in coastal waters off Buenos Aires Province, Argentine Sea

Abstract

Instituto Tecnologico de Chascomus (INTECH) Copepods are key components in the marine communities because of their important role in the transfer of matter and energy from primary producers to higher trophic levels and in the export of organic matter from the euphotic to deeper layers of the oceans (CALBET et al., 2000). Because of their role as prey for fishes at different stages of development, knowledge of zooplankton abundance and biomass in spatial and temporal scales remains a key element of the marine ecosystem approaches (IRIGOIEN et al., 2009). In fisheries science, accurate estimations of abundance, biomass and production of the different components of the food webs are necessary for the construction and implementation of ecosystem models th(CHRISTENSEN; PAULY, 1992). Paracalanus parvus , Ctenocalanus vanus, Calanoides carinatus and Oithona nana are dominant copepod species (50-100 %) in the coastal waters of the Argentine Sea (RAMIREZ, 1981; VINAS et al., 2002). These copepods play an important role in the pelagic food web as the main prey item for larvae (CIECHOMSKI; WEISS, 1974; VINAS; RAMIREZ, 1996) and juveniles and adults of anchovy (ANGELESCU, 1982; PAJARO, 2002). Thus, an accurate estimation of their biomass and productivity is necessary to quantify the transfer of matter and energy across the planktonic food webs. So far, there is only one regional work in which the individual biomass of copepods has been estimated (FERNANDEZ ARAOZ, 1991) in the Argentine Sea, but early copepodite stages were not included because of the mesh size ( ≥ 220 µm) employed. Our aim was to estimate the individual biomass of all the stages of the above-mentioned copepods by the geometric method and to establish, for each species, significant regression models predicting biovolume from some linear body dimension. Volumetric methods, such as the one employed in the present study, are the only choice if samples are also to be used for taxonomic purposes (POSTEL et al., 2000) and the geometric approach is the only suitable in the case of small-sized zooplankton (OMORI; IKEDA, 1984). The conversion of our results into another biomass proxy from the literature may easily be made. In fact, body wet weight can be derived from measurements of body biovolume by applying a factor of 1 for specific gravity (OMORI and IKEDA, 1984). Dry weight can be obtained by multiplying the wet weight by 0.20 and the carbon content can be considered as 40 % of the dry weight (POSTEL et al., 2000). Samples were obtained on October 18