Stability and resilience in coastal copepod assemblages: The case of the Mediterranean long-term ecological research at Station MC (LTER-MC)

摘要

We analyzed the copepod assemblages over two decades (1984-2006) in a coastal ongoing time-series at Station MC in the inner Gulf of Naples (Tyrrhenian Sea, Western Mediterranean), which is part of the International network of Long-Term Ecological Research (LTER). The seasonal and interannual time courses of species abundance and composition were related to depth integrated temperature, salinity, and chlorophyll a, which provide essential information on the local environmental dynamics. Our aims were to characterize the main modes of copepod variability and to highlight possible changes occurred in the period in relation to the local environmental dynamics. Despite the great variability at seasonal and interannual scales, our site did not show evidence of discontinuities or trends in water column properties as compared to other Mediterranean sites for the same period, which we interpret as resulting from the position of Station MC that is exposed to the influence of a complex climate forcing. Abrupt changes did not appear for most of the key representative species (e.g., Acartia clausi, Centropages typicus. Paracal-anus parvus, Temora stylifera, and juveniles of Clausocalanus spp./P. parvus) beyond the high interannual variability in the abundance patterns. A few indications suggest that our station might have acquired less coastal characters (e.g., decreasing chlorophyll a concentrations), but the signals from the copepod assemblages appeared only in rare species. A significant increase was observed in the occurrence of some typical offshore calanoids (e.g., Neocalanus gracilis, Scolecithricella spp.), while a few species typical of confined areas disappeared (e.g., Acartia margalefi, Paracartia latisetosa). STATICO analysis showed a significant resilience in the seasonal cycle of the copepod assemblages at Station MC, even when there was high variability in the environmental parameters. While the changes recorded in the least abundant species may be indicative of long-term variations, we interpret the overall persistence of the basic community as resulting from the flexibility of coastal species to adapt to variation in environmental conditions.