Population dynamics of the seagrass Posidonia oceanica for evaluating meadow health status: a case study using reconstruction techniques

Fish assemblages associated with 'coralligenous formations' in SE Apulia (Lower Adriatic and Ionian Seas, SE Italy) were studied by visual census to test for differences through time and over different spatial scales (i.e., among locations 3-4 km from each other, and among sites within locations 200-400 metres apart from each other). Thirty-two fish species were recorded, with sparids (eight species), labrids (seven) and serranids (five) being the families with most species. Fish assemblages were numerically dominated by Chromis chromis, Boops boops, and Coris julis. Multivariate analyses indicated significant differences in the structure of fish assemblages among times and locations (with C. chromis and C. julis mostly contributing to the observed dissimilarities), while sites within locations did not differ significantly. Temporal patterns of species richness differed both among locations and among sites within locations. Total fish abundance displayed different temporal trends at the smallest spatial scale examined (i.e., among sites within locations), whereas patterns over time in fish abundance without the contribution of gregarious species differed among locations only. The results show, therefore, that fish assemblages from coralligenous formations in SE Apulia might vary in time in spite of a fairly stable benthic environment. Temporal changes of the most important univariate variables (e.g., species richness) might thus differ among sites, locations or both. Factors acting at different spatial scales (e.g., habitat complexity, substrate slope) and through time (e.g., feeding displacements), probably involved in the variability of spatio-temporal patterns of fish assemblages, are discussed.