AZEITEIRO, U.M.M; IMAR – Institute of Marine Research, University of Coimbra: Distribution, Production, Histology and Histochemistry in the Acartia Genus (Calanoida: Copepoda) in a Temperate Estuary (Mondego Estuary, Portugal).

The Acartia genus is a key genus of the Mondego estuary (Western Portugal) and a relevant, widespread genus in all temperate estuarine zooplanktonic communities. Biomass/length relationships were estimated in the three species of the genus present in the estuary: A. tonsa, A. bifilosa var. inermis and A. clausi. Biomass/length relationships were estimated in Y=0.15e3.04x for A. tonsa, Y=0.084e3.03x for A, bifilosa var. inermis and Y=0.11e3.14x for A. clausi. Length-weight relationships were used to estimate production taking into account cohort growth and mortality. Annual production was calculated in 43.12 mg C m-3yr-1 for A. tonsa, 23 mg Cm-3 yr-1 for A. bifilosa var. inermis and 63.44 mg Cm-3 yr-1 for A. clausi and production/biomass (P/B) ratios were estimated, respectively, in 10.56, 28.96 and 25.50. These results indicate that the Acartia genus play a significant role in transferring energy to higher trophic levels in the system. Analyses of maturation stage of oocytes in adult ovigerous females of the species A. tonsa performed in two different periods of opposed abundance demonstrated the presence of all three considered oocytical development stages: immature, vitellogenic and mature, with emphasis in the latter since it indicates a permanent capability for reproduction despite the registered population abundance. Taking in account the relevance of the species, this fact demonstrates the modulating influence of ecological parameters in general zooplankton reproductive traits.