Persistence of benthic communities: a case study from the Valli di Comacchio, a Northern Adriatic lagoonal ecosystem (Italy)

Data collected from a 3 yr continuing sampling program were used to study the persistence of the macrofaunal communities living in the Valli di Comacchio (44°41'N, 12°10'E), a complex of shallow-water brackish lagoons located in the southernmost part of the Po River deltaic area (Italy). Univariate and multivariate analyses were used to assess the variability and persistence of the community at each of the 4 sites investigated. A total of 46 benthic taxa were identified from bottom grab samples: Annelida was the most abundant group, followed by Crustacea and Mollusca. The abundance of some species exhibited marked temporal fluctuations. At 3 out of 4 sites, abundance fluctuation were unpredictable in terms of both timing and magnitude. There was little evidence that factors operating at lagoon-wide scale contributed to variability in community structure. The balance of taxa within each community was probably most affected by forcing factors acting on a local scale. The perception of macrofaunal communities as being persistent through time decreased as the analysis moved from coarser (presence/absence) to finer (absolute abundance) levels of numerical resolution. Analyses showed that macrobenthic assemblages at some sites were both persistent and variable: this paradox reflected viewpoints of different analytical scales. Because of this, a multi-level approach is probably more useful in gaining insight into community persistence and variability