Ml. Decasabianca et al., IMPACT OF SHELLFISH FARMING EUTROPHICATION ON BENTHIC MACROPHYTE COMMUNITIES IN THE THAU LAGOON, FRANCE, Aquaculture international, 5(4), 1997, pp. 301-314
In a large marine lagoon (Thau lagoon, southern France) with a shellfi
sh farming dominant eutrophication, the macrophyte communities were sa
mpled by six transects of three depths (1.5, 2.5 and 5 m) and their ch
aracteristics (species composition, diversity and biomass) were descri
bed in relation to environmental and sediment parameters. With increas
ing eutrophication (total inorganic nitrogen, 0.140-0.295 mg 1(-1); di
ssolved reactive phosphorus, 0.045-0.110 mg 1(-1); and N/P atomic rati
o, 3-22), silt fraction and shell fragments in sediments increased (12
-93 and 0-65% dry wt respectively). Different types of macrophytic com
munities could be defined in the shallow zone (1.5-2.5 m) correspondin
g to four main and successive stages of degradation. A pure eelgrass s
tand (Zostera marina and Z. noltii) and an eelgrass community colonize
d by macroalgae weve observed in SW sites and could be distinguished b
y their sedimentary features. In sites (NE) move affected by eutrophic
ation (fine-textured sediment), available incident light determined tw
o main seaweed communities: an Ulva rigida community, outside the shel
lfish tables, and a Gracilaria bursa-pastoris community in the shellfi
sh tables (lower incident light).