Search

Insular assemblages of species are often considered unique because they are exposed to unpredictable patterns of colonization/extinction that depend on distance from other sources of colonists and on size of islands. An alternative explanation is that islands provide fundamentally different habitats of those of the mainland, regardless of any possible effect of size and isolation. These alternatives were examined by comparing assemblages of rocky shores on islands of the Tuscany Archipelago with those of the mainland in the same geographical region. Sandy beaches created a pattern of discrete areas of rock along the mainland with spatial discontinuities and extents comparable to those of the insular environment. Possible effects of isolation and size were therefore controlled in this study, so that one would expect no difference between islands and the mainland if only size and isolation matter. In contrast, differences are expected if historical events or other processes have distinct influences on assemblages in these environments. These hypotheses were tested by comparing assemblages of midshore and lowshore habitats of two islands with those of two similarly distributed locations on the mainland over a period of 2 years, using a hierarchical sampling design. Multivariate and univariate analyses revealed various patterns in the data. There were differences between islands and the mainland in structure of assemblages, in mean abundance of common taxa and in the magnitude of spatial and temporal variance in abundance in both habitats. Collectively, these findings support the model that islands in the Tuscany Archipelago have distinct assemblages from the mainland, thereby contributing to the regional diversity and complexity of assemblages of rocky shores over and above any possible effect of size or isolation. [Copyright &y& Elsevier]

Marine protected areas (MPAs) are increasingly used as a management tool to preserve species and habitats. Testing hypotheses about the effectiveness of MPAs is important for their implementation and to identify informative criteria to support management decisions. This study tested the general proposition that MPAs affected assemblages of algae and invertebrates between 0.0 and 0.5 m above the mean low water level of rocky coasts on two islands in the Tuscan Archipelago (northwest Mediterranean). Protection was concentrated mainly on the west coasts of the islands, raising the possibility that neither the full range of assemblages nor the relevant scales of variation were properly represented within MPAs. This motivated the comparison of assemblages on opposite sides of islands (habitats). The effects of MPAs and habitat were assessed with a multifactorial sampling design; hypotheses were tested about differences in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation. The design consisted of three replicate shores for each condition of protected and reference areas on the west side of each island and three unprotected shores on the eastern side. Assemblages were sampled independently four times on each island between June 1999 and January 2001. At each time of sampling two sites were selected randomly at each of two tidal heights to represent midshore and lowshore assemblages on each shore. Estimates of abundance were obtained using non-destructive sampling methods from five replicate 20×20 cm quadrats at each site. Results indicated differences among habitats in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation at the scale of shores. Most of these patterns were inconsistent with the predicted effect of management through MPAs. The data suggest that designation of MPAs in the Tuscan Archipelago should proceed through management of multiple shores and types of habitat selected to guarantee protection to a representative sample of assemblages and to the processes responsible for maintenance of spatial patchiness at different scales. This study also shows that considerations of spatial heterogeneity are important to underpin management decisions about the number, size and location of MPAs. [Copyright &y& Elsevier]