Andrea Rismondo

Seasonal pattern of Cymodocea nodosa biomass and production in the lagoon of Venice

Abstract Primary production and the biomass cycle of a shallow Cymodocea nodosa (Ucria) Ascherson meadow in the lagoon of Venice (Italy-Northern Adriatic) were measured from February 1993 to February 1994. Leaf growth was estimated by the Zieman method; rhizome production was estimated by marking rhizome terminals. All data showed a clear seasonality. In general, maximum growth was reached in July. Leaf production (a maximum of 12.3 g dry weight m−2 day−1 in July) and leaf biomass (a maximum of 810 g dry weight m−2) were much higher than in other Mediterranean localities. Cymodocea nodosa contributes significantly in stabilizing lagoon bottom sediments. The percentage of the belowground fraction of total biomass varied from 85% in winter to 58% in summer, and maximum shoot density was 2302 shoots m−2.

Sexual reproduction of Zostera noltii Hornemann in the lagoon of Venice (Italy, north Adriatic)

Abstract Flowering of Zostera noltii Hornemann in Venice lagoon (Italy, north Adriatic) has been observed in 1993 and 1994, from May to October. Measurements at three stations at different depth included vegetative and generative shoot density, number of spathes per generative shoot, length of spathes, numbers of male and female flowers and seed size.

Fuzziness and Heterogeneity of Benthic Metacommunities in a Complex Transitional System

We propose an extension to the metacommunity (MC) concept and a novel operational methodology that has the potential to refine the analysis of MC structure at different hierarchical levels. We show that assemblages of species can also be seen as assemblages of abstract subregional habitat-related metacommunities (habMCs). This intrinsically fuzzy concept recognizes the existence of habMCs that are typically associated with given habitats, while allowing for the mixing and superposition of different habMCs in all sites and for boundaries among subregions that are neither spatially sharp nor temporally constant. The combination of fuzzy clustering and direct gradient analysis permits us to 1) objectively identify the number of habMCs that are present in a region as well as their spatial distributions and relative weights at different sites; 2) associate different subregions with different biological communities; and 3) quantitatively assess the affinities between habMCs and physical, morphological, biogeochemical, and environmental properties, thereby enabling an analysis of the roles and relative importance of various environmental parameters in shaping the spatial structure of a metacommunity. This concept and methodology offer the possibility of integrating the continuum and community unit concepts and of developing the concept of a habMC ecological niche. This approach also facilitates the practical application of the MC concept, which are not currently in common use. Applying these methods to macrophytobenthic and macrozoobenthic hard-substrate assemblages in the Venetian Lagoon, we identified a hierarchical organization of macrobenthic communities that associated different habMCs with different habitats. Our results demonstrate that different reference terms should be applied to different subregions to assess the ecological status of a waterbody and show that a combination of several environmental parameters describes the spatial heterogeneity of benthic communities much better than any single property can. Our results also emphasize the importance of considering heterogeneity and fuzziness when working in natural systems.