Abstract
Ecological aspects of 75 megabenthic bivalve species found on the south coast of Portugal (from Vila Real to Sagres) were studied based on the information provided by seasonal bivalve surveys from 2000 to 2007 (8600 hauls, simultaneously using a razor shell dredge and a clam dredge). Of the 75 species identified, 36 occurred less than 30 times, and thus were considered rare in the area. The remaining 39 bivalves were analysed according to their occurrence, bathymetric distribution, geographic preferences, seasonal preferences, burying-depth, beach exposure and river mouth proximity. All species belonging to the Pharidae and Solenidae families (razor shells) and most Tellinidae were significantly more frequent in the razor shell dredge (indicating deeper burying in the sediment), whilst the families Cardiidae and Donacidae were significantly more frequent in the clam dredge (indicating that these species are probably closer to the sediment surface). As for the season, most bivalve species occurred similarly in both seasons (19 sp; 49%), but a large proportion were more abundant during the autumn surveys (17 sp., 44%), whereas only three species were commoner during the spring surveys. Most species belonging to the families Cardiidae and Mactridae were commoner in the autumn surveys. The spatial distribution differed between species and cluster analysis identified four communities with greater geographic affinity. Species belonging to the family Cardiidae were preferably found in the western part (WB) and the eastern part (S) of the study area, whereas the families Donacidae, Mactridae and Tellinidae occurred mainly in the central area (EB) and the eastern (S) coastal sectors. Overall, shallower species (modal depth at 3-6 m) showed greater occurrences and abundances than the deeper ones, and the depth pattern observed did not change between seasons. Donacidae and Mactridae (except Mactra glauca ) were represented essentially by shallow species, whereas Cardiidae (except Acanthocardia tuberculata and Cerastoderma edule ) included mostly species occurring in deeper waters. Bathymetric sequence of species distribution within some families was observed.
Highlights
Faunistic studies provide essential tools for understanding the dynamics of exploited communities and other inter-specific relationships (Pearson and Mannvik, 1998; Teske and Wooldridge, 2001; Abelló et al, 2002; Laudien et al, 2007)
SUMMARY: Ecological aspects of 75 megabenthic bivalve species found on the south coast of Portugal were studied based on the information provided by seasonal bivalve surveys from 2000 to 2007 (8600 hauls, simultaneously using a razor shell dredge and a clam dredge)
All species belonging to the Pharidae and Solenidae families and most Tellinidae were significantly more frequent in the razor shell dredge, whilst the families Cardiidae and Donacidae were significantly more frequent in the clam dredge
Summary
Faunistic studies provide essential tools for understanding the dynamics of exploited communities and other inter-specific relationships (Pearson and Mannvik, 1998; Teske and Wooldridge, 2001; Abelló et al, 2002; Laudien et al, 2007). Benthic communities have long been recognised as a good tool for monitoring either man-induced or natural long-term changes in marine ecosystems (Grémare et al, 1998). Marine environmental impact/monitoring studies are usually done through macrofauna sampling, which involves expensive and laborious procedures (Thrush et al, 1994; Chícharo et al, 2002; Fugi, 2007; McBreen et al, 2008). Bivalves constitute a large fraction of the littoral benthic communities and play essential roles in ecosystems as agents of sediment structuring (Reise, 2002), as a food item of many species (Ansell et al, 1999), and as contributors to biogenic sediment formation. Long term data series can provide valuable information on species ecology through the analysis of individual occurrences in relation to environmental variables
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