A quantitative study of the seagrass and algal meadows of the Spaanse Water, Curacao, the Netherlands Antilles

The Spaanse Water is a relatively turbid, 3.19 km(2) inland bay of virtually oceanic salinities and contains the largest seagrass, algal and mangrove areas of the Curacao Underwater Park. During 1989 and 1990, a quantitative community assessment of the larger attached flora and fauna of the seagrass and algal meadows of the bay was conducted at 151 6 m(2) stations using a quadrat sampling technique. A total of 13 different assemblages were distinguished. Shallow assemblages were dominated by Thalassia testudinum and Halimeda opuntia. As depth increased and light levels decreased, Thalassia gave way to increased coverages of especially H. opuntia, H. incrassata, Cladophora sp. and Caulerpa verticillata. In areas with significant availability of hard substrate an assemblage characterised (though not dominated) by corals was found at depths of 0-2 m, while sponges were concentrated at depths of about 4 m. The richest assemblages were found in shallow areas with high light levels and where a mix of both hard and soft substrate occurred. Assemblages with the lowest species richness were typically associated with low light intensities, soupy muds or homogeneous sandy sediments of high grain size.