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Two plankton mesh sizes of 67 µm and 220 µm were compared to evaluate their efficiency in the capture of the smallest copepods and appendicularians present in the Buenos Aires coastal area (Argentine Sea). A total of 12 copepod species and one appendicularian species were recorded in this study. The copepods were separated into 4 groups: harpacticoids, cyclopoids, small calanoids and large calanoids and their developmental stages. Among the cyclopoids, Oithona nana was the most abundant species, being 96.29 % underestimated by the 220 µm mesh, whereas Microsetella norvegica dominated the harpacticoids and was captured exclusively by the smaller mesh. Similar results were found for copepodites I-III of small calanoids, whose net sampled underestimation reached 99.70%. On the other hand, no significant difference between meshes was found for adults and copepodites IV-V of small calanoids or any of the developmental stages of large calanoids. A great loss of biomass was observed for O. nana when applying the larger mesh. In regards to the appendicularian Oikopleura dioica, all size ranges below 1,000 µm length were better estimated by the 67 µm mesh in terms of abundance and biomass. Our results clearly show that the 67 µm mesh was more efficient in the capture of early stages of small copepods thus providing a more accurate estimation of the fish larvae prey field. Compararam-se os copépodos e apendiculárias coletados, na zona costeira do Estado de Buenos Aires (Argentina), com duas redes de plâncton, tipo mini-bongo, de abertura de malha de 67 µm e 220 µm. Registraram-se 12 espécies de copépodos e uma de apendiculária. Os copépodos foram separados de acordo com as categorias: harpaticoides, ciclopoides, e calanoides pequenos e grandes. O cálculo da abundância de Oithona nana, que foi a espécie mais abundante no material analizado, demonstrou que a coleta com rede de 220 µm teve uma subestimativa de 92,29%, em relação à coleta com a rede de 67 µm, o que resultou numa alta perda de biomassa, dessa espécie, quando usada a rede de 220 µm. Outro dado relevante, foi a dominância de Microsetella norvegica, dentro dos harpaticoides, e a presença da mesma somente no material coletado com a rede de 67 µm. De igual forma, quando se analisou a abundância dos copepoditos I-III dos pequenos calanoides, a rede de 220 µm demonstrou uma subestimativa de 99,70%, em comparação com a rede de 67 µm. Não foram encontradas diferenças significativas na coleta de adultos e copepoditos IV-V dos pequenos calanóides e todos estagios grandes calanóides. Para as apendiculárias, no que diz respeito à abundância e biomassa, as variações de tamanho menores que 1,000 µm, foram melhor estimadas com a malha de 67 µm. Os resultados demonstraram que a malha de 67 µm foi mais eficiente na coleta dos ciclopoides e dos primeiros estágios de copepoditos dos pequenos calanoides, que por sua vez, constituem a principal fonte de alimento para as larvas de teleostei na área analisada

brazilian journal of oceanography

Capture efficiency for small dominant mesozooplankters (Copepoda, Appendicularia) off Buenos Aires Province (34ºS-41ºS), Argentine Sea, using two plankton mesh sizes