Relative influences of space, time and environment on coastal ichthyoplankton assemblages along a temperate rocky shore

Abstract

Fish egg and larval assemblages, and the factors that drive them in the nearshore environment remain largely unknown. In this study, two sampling methods were used to assess the relative influences of space, time and environment on ichthyoplankton communities at nearshore stations, near the Cerbere-Banyuls Marine Protected Area (France), during spring and summer 2003. Resulting data sets were analysed by variation partitioning, with redundancy analysis to estimate variance fractions based on adjusted R(2). A total of 42 environmental descriptors were considered for the analyses. The descriptors that best explained the variance of the data set were selected to build models. Analyses of the relative influences show that the environmental conditions drive egg and larval density variations, specifically depth, currents and wind directions. However, time and space combined with environmental factors also contribute substantially to ichthyoplankton variability. The combined effect of space and environment is likely to be generated by the influence of the coast profile on ichthyoplankton from shallower water. At deeper stations, wind and current fluctuations result in a combined effect of time and environment in relation to eggs. These results strongly suggest that the nearshore area influence is between 25 and 30 m depth and is separated from the inner continental shelf. We propose the hypothesis that the rocky shore ecosystem is favourable for coastal accumulation and/or retention of ichthyoplankton.