SALT AND WATER BALANCE IN TWO MARINE SPIDER CRABS, LIBINIA EMARGINATA AND PUGETTIA PRODUCTA. II. APPARENT WATER PERMEABILITY

Abstract

1. Estimates of osmotic water permeability suggest that Libinia emarginata [166 µl/(g·hr·osmol)] is less permeable to water than Pugettia producta [338 µl/ (g·hr·osmol)]. Data on tracer water exchange supports this conclusion and the differences in apparent permeability can be correlated with differences in habitat. 2. Short-term changes in DO water exchange were examined in specimens of Carcinus maenas and Libinia emarginata. When these crabs were transferred from 100 to 80% sea water, there was an initial reduction in k in (1/hr), the hourly water exchange fraction, of from 1.9 to 1.4 and from 5.8 to 4.3 in Carcinus and Libinia, respectively. In both crabs, the initial response to the dilute medium is similar; however, in Libinia, the reduction in k is transient while in Carcinus it is a long-term response. 3. Estimates of osmotic (P*) and diffusive (P*) water permeabilities for Carcinus, Libinia and Pugettia indicate that the ratio of P*/P* is about 2, which suggests that unstirred layers could have a major influence on tracer water movement in all of these crabs. It is proposed that the initial changes in k, which occur during adaptation to a dilute medium, are at least partly the result of an increase in thickness of the unstirred layers surrounding the gills, caused by a reduction in the flow of medium through the gill chamber.

Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers – mortality and damage seen in simulation experiments

“…In some studies, mortality was described as being due to ''bursting'' where bulk fluid losses through the exoskeleton occurred. Body mass increases have also been reported and, in some species, these were restored to the original with time (Schwabe, 1933;Cornell, 1980). We found mass gains of a similar order in Nephrops suggesting a large and rapid uptake of water.…”

Feeding and digestion in low salinity in an osmoconforming crab, Cancer gracilis I. Cardiovascular and respiratory responses

“…Weaker regulators tend to become inactive (Sugarman et al, 1983;McGaw et al, 1999) and show no change in oxygen uptake (Brown and Terwilliger, 1999) and mixed cardiac responses (McGaw and McMahon, 1996;McGaw and McMahon, 2003;McGaw, 2006a;Dufort et al, 2001). Osmoconformers show a decrease in activity (McGaw et al, 1999) (D. L. Curtis, E. K. Jensen and I. J. McGaw, manuscript submitted for publication) and cardiac and respiratory parameters (Figs·3, 4) (Spaargaren, 1973;Cornell, 1973;Cornell, 1974;Cornell, 1979;Savant and Amte, 1995).…”

“…Studies on cardiac and respiratory responses of osmoconforming species of decapod crustaceans are very limited. In contrast to species that are able to hold the body fluid concentration above that of the medium, osmoconforming species exhibit a bradycardia (Spaargaren, 1973;Cornell, 1973;Cornell, 1974;Cornell, 1979) and a decrease in oxygen uptake (Savant and Amte, 1995).…”

The pyloric neural circuit of the herbivorous crabPugettia productashows limited sensitivity to several neuromodulators that elicit robust effects in more opportunistically feeding decapods

“…This effect was fully reversible, and the complete pyloric pattern was restored within 2-3·min after the sucrose was replaced with saline ( Fig.·3). We considered the possibility that this level of dependence on modulatory input was an artifact of the saline used in the experiments, and so tried a number of saline formulations, based on other decapod salines as well as on the measured concentrations of ions in P. producta hemolymph (Cornell, 1979). A physiological saline formulation based on one routinely used for C. borealis , another brachyuran crab, was used in all physiological experiments as it gave the fastest recovery from sucrose block.…”