Distribution, production, histology and histochemistry in Acartia tonsa (Copepoda: Calanoida) as means for life history determination in a temperate estuary (Mondego estuary, Portugal)

Acartia tonsa is a key species in the Mondego estuary and a widespread species in all temperate estuarine zooplankton communities; a fact that bestows high relevance upon the outcome of this study. One of the purposes of this study was to estimate the distribution, production and production/biomass ratio values of A. tonsa. Biomass/length relationship was estimated as follows: Y = 0.15e(3.04x). Length-weight relationships were used to estimate production taking into account cohort growth and mortality. The annual production was calculated to be 43.12 mg Cm-3 year(-1) and the production/biomass (P/(B) over bar) ratio was estimated to be 10.56. The other purpose of this study was to use histology, histochemistry and biometry to determine as to whether fecundity is a limiting factor in itself or are zooplankters constrained to respond to an ever changing environment. Analyses of the maturation stage of oocytes in adult ovigerous females performed in two different periods of opposed abundance (February-high abundance, representing maximum fertility-and September-low abundance, representing "sterility") demonstrated the presence of all three considered oocytical development stages: immature, vitellogenic and mature; with emphasis on the latter since it indicates a permanent capability for reproduction despite the registered population abundances. Taking into account the relevance of the species. this fact demonstrates the modulating influence of ecological parameters on general zooplankton reproductive traits. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.