oa African Zoology - The Osmoregulatory ability of three Grapsoid Crap species in regulation to their penetration of an Estuarine

Volume 10, Issue 2
  • ISSN : 1562-7020
  • E-ISSN: 2224-073X



The oamoreaulatory abilities of the Grapsoid crabs Cyclograsus punctatus, Sesarma and Sesarma eulimene were studied comparatively in an attempt to explain, at least in part, their distribution in estuaries. Both survival and haemolymph osmotic pressure were used as indices of hyperosmotic regulatory ability. All three species were shown to be capable of Regulations their haemolymph osmotic pressure against lowered external salinities. S. eulimene was found to be better able to control its haemolymph concentration in very low salinities than S. catenata, which would account for the former�s occurrence the upper reaches of estuaries. C.punctatus was shown to be capable of maintaining its haemolymph osmotic pressure above that of the environmental medium in lowered salinities, but without the degree constancy characteristics of the two Sesarama species. It does, however, show a marked ability tolerate lowered internal osmotic pressure, an ability which appear to develop in response to partial dilution of the haemolymph. These adaptations, together with its semi-terrestrial habit as a shore crab, suffice to enable C.punctatus to penetrate an estuary to almost the same extent as S. Catenata.

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