Ecology and trophic links of macroinvertebrates in a dune slack of a Mediterranean coastal ecosystem (Grosseto, Italy)

Abstract

Along a Tyrrhenian coastal ecosystem the macroinvertebrates of a dune slack were studied to assess food webs, guilds and the possible links with other beach compartments. Environmental monitoring was conducted for an entire year through beach profiling, collection of the vegetation, of substrate samples and of the chemico-physical parameters of the ground water. Macroinvertebrates were assessed seasonally with two line transects of pitfall traps whereas monthly captures were carried out for coleopterans only. Zonations were also calculated to subdivide dune slack residents from nonresidents. The plant and invertebrate specie were then grouped using Hierarchical Cluster analysis. Canonical Correspondence Analysis was instead used to evaluate the effect of the environmental parameters of the dune slack on the vegetation structure and macroinvertebrate composition. To evaluate the relative contribution of the different food sources to the diets of the macroinvertebrates a Bayesian stable isotope mixing model was employed. The study clearly showed that the inhabiting dune slack fauna was subdivided in two main guilds of non-predator and predator species and that slacks could be used all year round by resident species adopting particular behaviours or avoiding interspecific competition by modulating their spatial and temporal strategies. Furthermore slacks were exploited as nursery grounds for immature stages of specific species and in other cases as important feeding areas for predators. These findings indicated that macroinvertebrates exploited beach compartments according to the different stages of their life-cycle and that the integrity of the entire beach ecosystem is a key factor to promote a high biodiversity in a sandy beach-dune ecosystem.