Seasonal Variation of a Deposit-Feeder Assemblage and Sedimentary Organic Matter in a Brackish Basin Mudflat (Western Mediterranean, Italy)

Abstract

From summer 1996 through to autumn 1997 the seasonal changes of a macrofaunal assemblage, the nutritional value of organic matter (as content of lipids, proteins and carbohydrates) and the content of chlorophylla in a Mediterranean mudflat were analysed. Sediment for macrofauna and biochemical analyses (chlorophylla, lipids, proteins, and carbohydrates) was collected using a three-way nested sampling design. Results indicated differences in the composition of organic matter especially in summer 1997 and at all the other seasonal periods of sampling. In summer 1997 a sharp increase of protein concentration was measured. Chlorophylla showed large fluctuations within seasons, especially during autumn and winter.Capitella cf. capitata, Pettiboneia urciensis, Streblospio shrubsolii, Desdemona ornata, Perinereis cultrifera, Abra segmentum and Oligochaeta dominated the assemblage. Species composition was different between autumn 1996 and 1997. Increasing abundance ofStreblospio shrubsolii , Capitella cf. capitata and Desdemona ornata was found from summer through to autumn 1997. Oligochaeta increased in autumn 1997. Perinereis cultrifera and Abra segmentum fluctuated with high values in winter and spring.Significant correlation coefficients (P<0·05) were found for the abundance of Streblospio shrubsolii and Desdemona ornata with proteins in summer 1997 and for Perinereis cultrifera with chlorophylla in autumn 1997. Correlations (at P<0·1) were also detected for Capitella cf. capitata with proteins in summer 1997 and for Perinereis cultrifera with chlorophylla in winter.These results suggested that availability of sedimentary food resources might be important in regulating the dynamics of deposit feeders. Availability of nitrogen compounds (i.e. proteins) may regulate population growth during the warm season. Microalgae, as estimated by chlorophylla, may be important for some selective deposit-feeders during the cold season.