DECAPOD CRUSTACEAN COMMUNITIES FROM CALCAREOUS SEAWEED AND POSIDONIA-OCEANICA (RHIZOME STRATUM) IN SHALLOW WATERS

Quantitative decapod studies carried out on calcareous seaweeds and Po sidonia oceanica beds (mainly rhizome stratum), from shallow coastal w aters of Almeria (S, SE Spain), revealed that these biotopes represent part of the habitat of the same decapod crustacean community. A gradu al transition from the decapod community in Posidonia to those in calc areous concretions is shown. This transition appears to depend on the relative developments of, and the interrelations between, both biotope s, as well as on the influence of a number of extrinsic factors such a s the presence of crevices, photophilic seaweeds and sedimentation. Ho wever when these two biotopes are well developed and independent they could be recognized by their differing quantitative species compositio ns, that is by the high dominance of a small number of and different s pecies.