Short-term response of deposit-feeders to an increase of the nutritive value of the sediment through seasons in an intertidal mudflat (Western Mediterranean, Italy)

In coastal intertidal flats, assemblages of deposit-feeders often vary seasonally and according to the availability of food in sediments. In the mudflat where this study has been done, the deposit-feeder assemblage changed after a sharp increase of fresh detritus, which occurred in summer 1997. The number of the animals increased and abundances of some worms (Streblospio shrubsolii, Desdemona ornata and Capitella cf. capitata) were correlated with the nutritive value of the sediment. In addition, there was evidence that increasing food in summer would increase recruitment of juveniles and adults of S. shrubsolii.In this paper, the concentration of food was manipulated in situ in sediments of an intertidal mudflat in different seasons. Food of high nutritive value was added to small plots of sediments to test hypotheses about effects on the distribution of deposit-feeders. It was predicted that addition of food would change composition and abundance of the assemblage and densities of the deposit-feeders that were correlated to the availability of food. Furthermore, it was tested whether juveniles and adults of S. shrubsolii were affected by the availability of food consistently through seasons.Densities of deposit-feeders increased in plots where the sediment was organically enriched. The composition of the assemblage, however, was not affected. S. shrubsolii, D. ornata and C. cf. capitata responded to the addition of food. However, the nutritive value of the sediment affected the dynamics of these animals variably through seasons. Abundances increased in the experimental treatment E in winter and spring for D. ornata and in winter and autumn for C. cf. capitata. Furthermore, in summer and autumn juveniles and adults of S. shrubsolii were more abundant in plots where food was added.