Macrobenthos ofPotamogeton andMyriophyllum beds in the upper reaches of Canal de Mira (Ria de Aveiro, NW Portugal): Community structure and environmental factors

Abstract

The community structure of the macrobenthic fauna (>0.5 mm) ofPotamogeton andMyriophyllum beds of the upper reaches of Canal de Mira (0.5<Sal<5) was studied monthly from May 1988 to April 1989 at three sampling stations. Environmental data included water, sediment and vegetation parameters measured monthly or seasonally. Four 24 hours sampling cycles were carried out in June, September and December 1988 and March 1989. The faunal data were subjected to ordination techniques (MDS) and a permutation test (two-way crossed layout) was used to assess spatial and temporal differences. The results showed significant differences between stations and a strong seasonal pattern in the community structure. The species responsible for sample groupings were determined by discriminant analysis using Bray-Curtis dissimilarities, and the faunal assemblages were studied in relation to the environmental factors. The results indicate that the main structuring factors of the community are plant biomass and water salinity at low tide. Station 2 exhibits both the highest values of plant biomass (DW=289 g m−2) and of macrofauna density (369, 240 ind m−2).Potamopyrgus jenkinsi, Corophium multisetosum andLimnodrilus hoffmeisteri are dominant species in the study area. The community of station 1 includes an important set of taxa usually associated to freshwater habitats (oligochaetes, leeches and insect larvae) whilst in station 3 typically estuarine species (Cyathura carinata, Leptocheirus pilosus, Nereis diversicolor, Streblospio shrubsolii) occur. A succession of peak densities of different taxonomic groups during the year indicates seasonal variation in the community structure. The faunal assemblage of the study area is compared with similar ones in NE Atlantic and Mediterranean coastal systems.