DISTRIBUTION PATTERNS OF TROPICAL ESTUARINE BRACHYURAN CRABS IN THE GULF-OF-MEXICO

Distribution patterns are defined for 20 brachyuran crab species of La guna de Terminos based on the range of salinity and the habitats occup ied by each. Habitats include unvegetated soft substrates. macroalgae, and sea grasses. ''Wide'' and ''restricted'' distributions relate spe cies abundance to a wide and a narrow salinity range, whereas ''associ ated with the habitat'' and ''not associated with the habitat'' consid er the presence of a species in one or several types of habitat. Fourt een species were grouped in the restricted and associated with the hab itat pattern, of which the 3 spider crabs and the 10 mud crabs were as sociated with submerged aquatic vegetation in salinities above 18 part s per thousand, and the swimming crab Callinectes exasperatus was dist ributed in an adjacent limnetic lagoon on unvegetated soft substrates. The mud crab Dyspanopeus texanus was placed in the wide and associate d with the habitat pattern, since it is a euryhaline species and was a lways found on macroalgae and sea grasses. Three other swimming crabs and two other mud crabs were found on all sorts of substrates along a wide range of salinity and were included in the wide and not associate d with the habitat pattern. Six faunistic groups were formed after ana lysis of the abundance data, using an ordination method with axes defi ned by salinity and type of habitat. Four functional guilds of brachyu ran crabs are proposed, based on the 3 distribution patterns, the 6 fa unistic groups, and the 2 subsystems and 4 areas previously described for the lagoon. Guild A grouped 2 swimming crabs and 1 mud crab distri buted along the areas of the lagoon directly influenced by river runof f, where detritus-rich unvegetated soft substrates and macroalgae are common. Guild B included: (I) the 3 spider crabs and most of the mud c rabs of which seven restricted and associated with the habitat species congregated in the northcentral-northeastern subsystem of the lagoon, where the greatest heterogeneity of habitats, dense sea-grass beds an d poly-euhaline environments, is common; (2) 5 restricted and associat ed with the habitat species mostly distributed in this subsystem were also collected in areas influenced by river runoff during the dry seas ons when salinity was above 24 parts per thousand; and (3) 2 wide and not associated with the habitat species were mostly found in this subs ystem, but extended their distribution to areas without submerged vege tation and lower salinities. Guild C was represented by D. texanus, wh ich was found throughout most of the lagoon on macroalgae and sea-gras s beds. Guild D included Callinectes sapidus and C. similis that were distributed throughout the lagoon independently of a particular type o f habitat.