The distribution of estuarine fish larvae: Nutritional condition and co-occurrence with predators and prey

Fish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters we re registered and zooplankton samples were obtained simultaneously. Densiti es of fish larvae (ind.100 m(-3)) were calculated from 211 samples and larv al nutritional condition measured as RNA/DNA ratios were obtained for 346 i ndividuals, using a fluorimetric method for nucleic acid quantification. Co rrelating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors a ffecting within-year trends in abundance and nutritional condition of estua rine fish larvae. Results indicated that: 1) the abundance of fish larvae s eems conditioned by temperature and predation; and 2) their nutritional con dition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the beha viour and physiology of fish larvae. Furthermore, the co-occurrence of pred ators and larvae might be related to similar feeding patterns or comensalis m. Whenever feeding conditions are suitable, they usually determine enhance d growth and nutritional condition. However, predation seems to control thi s latter relationship through its effect on larval mortality. (C) 2000 Edit ions scientifiques et Medicales Elsevier SAS.