Predicting amphipods' brood size variation in brackish environments: an empirical model for Corophium multisetosum Stock, 1952 (Corophiidae) in Ria de Aveiro (NW Portugal).

Data on fecundity of Corophium multisetosum from Areão (Ria de Aveiro, Portugal) are analysed by non linear regression to quantify the relationship between brood size (N(e)) and head length (L(h), in mm), water temperature (T, in degrees Celsius) and salinity (S, in psu). The aim of the analysis is to obtain a simple line N(e)=a+bL(h), in which the slope (b) and the y intercept (a) are functions of salinity and/or temperature on each sampling occasion. The equation N(e)=(-2.940-8.027S)+(-89.431+18.171S+12.904T-0.368T(2))L(h) explains 64% of the variability of brood size throughout the breeding period. The model predicts an optimal temperature around 18 degrees C and a very low fecundity at low salinities. The graphical comparison of the lines obtained by the model and by a usual linear regression illustrates its potential usefulness to predict fecundity changes. The authors suggest that the observed variation in the fecundity of other brackish-water amphipods can be described and predicted using similar models.