PHYSICOCHEMICAL AND BIOLOGICAL STRESSORS 133 



colored. When a female undergoes the molt of puberty, her abdomen 

 darkens, becomxing virtually identical in color to the dorsal surface of 

 her carapace. When she spawns, the egg mass distends the abdomen 

 from her ventral surface so that it is held behind her, as in a lobster, 

 thereby maintaining countershading. This must have particular 

 adaptive value in higher salinities w^here females spawn and hatch 

 their eggs. 



The upper surfaces of Caribbean portunids' carapaces match 

 substrata to varying degrees. The freshwater Callinectes can be found 

 on widely different substratum colors and textures. Coloration in 

 C. bocourti (bright reddish brown and dull green tones) and in 

 C. maracaiboensis (highly variable, ranging from ashen gray to dark 

 chocolate brown) is cryptic in some environments but somewhat 

 conspicuous in others. In contrast, portunids from higher salinities 

 occur on fewer substrate types and, with one notable exception, 

 are better camouflaged. For example, ground colors in Portimus 

 anceps (Saussure), P. depressifrons (Stimpson), and Arenaeus 

 cribrarius (Lamarck) are very light (white, gray, and tan), with 

 disruptive markings that render them extremely inconspicuous 

 against the light calcareous sediments on and in which they live. The 

 species from the most equable climates I studied, marine lagoons 

 and coral reefs, has almost completely eschewed cryptic coloration. 

 Portunus sebae (H. Milne Edwards), apparently a strictly nocturnal 

 species, has two unmistakable white-ringed black ocelli on the 

 posterior half of its carapace; this is startle coloration, which it shares 

 with some coral-reef octopuses and stomatopods and with terrestrial 

 moths and mantids. These ocelli have probably evolved as deterrents 

 to goatfishes and triggerfishes, which "blow" into reefal sands as 

 they forage during the day. 



As Stephenson (1962) stated, swimming crabs are also diggers, 

 and those I observed in the field spend a large fraction of their time 

 buried in soft substrata, usually with only their eyes, antennae, and 

 antennules protruding. Not surprisingly, their eyes are cryptically 

 colored to varying degrees. Eyes of freshwater Callinectes have dark 

 and light barred or checked patterns, which make them somewhat 

 more conspicuous than the light-colored, often stippled eyes of 

 species from higher salinities, including P. sebae. Demersal portunids 

 have ridged, pilose, or granulose carapaces that retain sediments 

 when the crabs have partly or completely emerged from the 

 substratum, thereby disrupting their form and permitting a degree of 

 camouflage even on substrates that their carapace colors do not 

 match closely. As in carapace and eye coloration, there is a trend in 

 carapace texturing among species along the gradient. Freshwater 



