The osmotic behaviour of a number of grapsoid crabs with respect to their differential penetration of an estuarine system.

During the last thirty years there has been a large volume of work published on the osmotic behaviour of invertebrate animals (recently reviewed by Kinne, 1964 and Potts & Parry, 1964), of which much has concerned the Brachyura (see reviews by Robertson, i960 and Lockwood, 1962). Most of this attention has been directed towards what can be termed 'a purely physiological end-point', comparatively little having been orientated towards ecology, although distributional aspects have been emphasised by Topping & Fuller (1942), Panikkar (1951) and Kinne (1963). The osmotic behaviour of a number of crabs exhibiting differential zonations up a shore, from sublittoral to semi-terrestrial species, has been documented by Pearse (1932). These crabs were not taken from one particular littoral region, however, but were composed of different species from completely separate regions. Although several workers, e.g. Teal (1958), Snelling (1959) and Ono (1965), have suggested that salinity is a major limiting factor to the distribution of crabs in estuarine or brackish environments, no work has been published on the osmotic behaviour of a group of inter-related crabs showing a differential distribution along a marineestuarine (-fresh water) series. This lack of data is no doubt to a large degree caused by the absence of such crab series in temperate regions (see Panikkar, 1940). Teal (1958) stated that salinity was probably one of the two major factors influencing the distribution of Uca spp. in a Georgia salt-marsh (the other being habitat preferences). Ono (1965), however, studying the distribution of a number of grapsoid crabs in the Tatara-Umi estuary in Japan, found that the upper limits of the distribution of most species were lower than the upper limits of the distributional range of the respectively suitable substrates. He deduced from field observations and salinity/ survival data that chlorinity was the most important factor limiting the upstream penetration of the crabs. Further, Snelling (1959), after a study of the distribution of the intertidal crabs of the Brisbane River, concluded that the limiting factor to their upstream penetration was the salinity, the distributions of the crabs changing in relation to salinity changes in the river caused by the amount of fresh water runoff into the upper reaches. The following is an investigation, with an ecological bias, of the osmoregulation capabilities of a group of grapsoid crabs, the majority related at the subfamilial level,