PHYSICOCHEMICAL AND BIOLOGICAL STRESSORS 



127 



TABLE 2 



SPECIES COMPOSITION (%) OF DEMERSAL PORTUNIDS 

 ALONG PACIFIC COLOMBIAN TRANSECTS 



Species 



River 



Continental shelf 



Upriver Midriver mouth 9m 18m 27 m 37 m 



0.9 



;5.7 43.2 31.5 



6.1 49.9 61.3 87.4 



7.6 



0.6 



5.3 



0.7 



7.2 12.6 



strongly dominated (>95%) by C. bellicosus (Stimpson), which was 

 completely absent from offshore trawl hauls in which I found great 

 numbers of C. arcuatus, some Portunus xantusii minimus Rathbun, 

 an E. robustus, and a handful of nonportunid brachyurans. Brusca 

 (1973) noted that E. robustus can be abundant in shrimp trawl hauls 

 in the northern gulf, presumably in deeper waters than I sampled. 

 Thus the Colombian and northern gulf gradients, although 

 ~5000 km apart, show striking similarities. The most terrestrially 

 influenced biotopes are dominated by different species (C toxotes 

 vs. C. bellicosus), but these are replaced to seaward by C. arcuatus, a 

 Portunus sp. {P. asper vs. P. xantusii minimus), and E. robustus. 



Although the Caribbean has more portunid species than the east 

 Pacific, salinity distributions (aside from the absence of extant 

 Caribbean Euphylax) in tropical and warm temperate areas are 

 similar at the generic level. Callinectes monopolize terrestrially 

 dominated waters, and Arenaeus, Portunus, Cronius, and fully 

 aquatic brachyurans in many other famihes make, at most, limited 

 incursions into hyposaline waters (Table 3). Among Jamaican 

 Callinectes, C. maracaiboensis, C. bocourti A. Milne Edwards, and C 

 sapidus Rathbun dominate the freshest sites. Ail seven common 

 species occur in the brackish range, C. exasperatus (Gerstaecker) 

 being the most abundant. In waters usually diluted slightly below 

 seawater values, C. marginatus (A. Milne Edwards), C. danae, and C. 



