PHYSICOCHEMICAL AND BIOLOGICAL STRESSORS 121 



There is an admission price, however; the species must have 

 morphological, physiological, behavioral, or life-historic adaptations 

 to abiotic and biological conditions that are increasingly alien and 

 stressful with increasing departure from the sea. If the group were in 

 some way preadapted for ecological expansiveness (weedy), repeated 

 invasions of the gradient extending from marine dominated to 

 terrestrially dominated aquatic climates would lead either to 

 one species' eliminating the others or to partitioning of the gradient. 

 This paper considers one group, bottom-dwelling swimming crabs of 

 the family Portunidae, which has repeatedly invaded this gradient. 

 Observations are given on species distributions, factors limiting 

 portunid incursions into estuaries, and factors resulting in coexis- 

 tence rather than in monopolization by a single species. Some of the 

 principles illustrated should be valid for other groups inhabiting 

 natural physicochemical gradients as well. 



The tropical American coasts have a small share of the world's 

 ~300 portunid species (Norse, 1977), but they do have most of the 

 species (members of the genus Callinectes) which are known or 

 believed to invade estuaries. The taxonomy of American portunids, 

 although less fluid than that of portunids from the Indo-West Pacific, 

 has been complicated by variations in areal distributions, abundance, 

 temporal fluctuations, and intensities of collecting. Many species are 

 sexually dimorphic and dichromatic, have allometric growth and vary 

 geographically, and, therefore, require considerable experience to 

 identify with confidence. In fact, newly described Portunus 

 (Holthuis, 1959; 1969) and Callinectes spp. (Williams, 1966; 

 Taissoun, 1972) have been added to the tropical west Atlantic fauna 

 in recent years. Unfortunately, C. sUjiilis Williams is still misidenti- 

 fied as C. ornatus Ordway or C. danae Smith by some scientists, and 

 I failed to realize fully that C maracaiboensis Taissoun, ostensibly a 

 Lake Maracaibo area endemic, was common in my main study area 

 (Norse, 1975; 1977). This taxonomic uncertainty has confused our 

 already limited view of the group's ecology, but identification of 

 eastern Pacific portunids and the world's Callinectes has been 

 greatly facilitated by the monographs of Garth and Stephenson 

 (1966) and Williams (1974). 



After studying the taxonomy of Callinectes, I visited Florida, 

 Jamaica, Curacao, both the Caribbean and Pacific coasts of Colom- 

 bia, and the Pacific coasts of Mexico and Panama (Fig. 1) to delimit 

 the ecological distributions of demersal portunids and the roles of 

 environmental factors contributing to them. This paper synthesizes 

 some of the results I have discussed in greater detail elsewhere 

 (Norse, 1975; 1977; in preparation; Norse and Estevez, 1977). 



