The Osmotic and Chloride Regulative Capacities of Five Hawaiian Decapod Crustaceansl FRED 1. KAMEMOT02 and KENNETH N. KATo3 THE IONIC and osmotic regulative capacities of ever, were collected from the same general area. crustacean species have been described by a The semiterrestrial grapsid crab, Metopograpsus number of investigators (see reviews by Krogh, messor (Forsk:'l.l) was collected from the mud 1939; Robertson, 1953, 1960; Ramsay, 1954; flats of Kuliouou. This animal was usually found Beadle, 1957; Lockwood, 1962, 1964; Potts under rocks and debris which littered the flats. and Parry, 1964). The most obvious and general Calappa hepatica (Linnaeus), a member of the conclusion which can be drawn from these in­ family Calappidae, was collected from the sand vestigations is that the aquatic crustaceans dis­ flats of Maunalua Bay. Thalamita crenata (La­ play varying degrees of responses to osmotic trielle), Podophthalmus vigil (Fabricius), and stress conditions. The animals' capacities to cope Portunus sanguinolentus (Herbst) are all rep­ with the osmotic changes in the environment resentatives of the family Portunidae. T. crenata range from non-regulation or osmoconforming is commonly found in brackish waters and was (the internal osmotic concentration maintained collected on the mud banks of Fort Kamehameha isosmotic to the environmental concentration) Reservation. P. vigil was trapped in 3 to 8 feet to hypo- and hyperosmotic regulation. The of water on the northeastern shore of Kaneohe majority of the crustaceans appear to have the Bay. P. sanguinolentus was collected on the ability to regulate to some degree, either osmo­ reefs of Keehi Lagoon. After each collecting tically or ionically, within this wide range of trip, the animals were brought back to the lab­ regulatory capacities. oratory and kept in aerated, 100 per cent sea In the present investigation, the responses of water (approximately 560 meq NaCl/1). Ex­ five Hawaiian decapod crustaceans to varying perimental salinities of 25, 50, and 75 per cent sea water concentrations were studied. These sea water were made by diluting 100 per cent five species were selected for study because of sea water with appropriate amounts of tap their· ready availability in the shallow coastal water. waters off the island of Oahu. This investigation Animals were randomly selected without dis­ was undertaken to obtain basic information on crimination as to sex. Only animals in the in­ osmoregulation in the common Hawaiian species termolt stage were used for all of the experi­ which can be maintained in the laboratory and ments. For C. hepatica and the three portunids, which may serve in further investigations on the the experimental media completely covered the mechanisms of salt and water balance in crus­ animals. M. messor, however, was placed in taceans. water depths which permitted the animals to lift themselves above the water when they so desired. MATERIALS AND METHODS All animals were transferred directly into their test media from normal 100 per cent sea water. The five species of crabs were collected from At the end of a 24-hour exposure to the test various locations along the coastline of Oahu, media, the blood was analyzed for osmotic Hawaii. All animals of the same species, how- and chloride concentrations. Ten animals were l Supported by Grant GB-673 from the National used in each experimental group. Blood was Science Foundation. Manuscript received July 27, 1968. obtained by puncturing the arthrodial membrane 2 Department of Zoology, University of Hawaii, between the fourth and fifth thoracic appendages Honolulu, Hawaii 96822. with a finely drawn capillary tube. The blood 3 Present address: Department of Physiology and Biophysics, University of Illinois, Urbana, Illinois was expelled into a centrifuge tube and an equal 61801. volume of distilled water was added and thor- 232 Regulative Capacities of Crustaceans-KAMEMoTo AND KATO 233 oughly mixed. Dilution was necessary to prevent osmotic concentrations when the animals are total coagulation of the blood. The samples were subjected to sea water concentrations of varying centrifuged for 10 minutes at 10,000 rpm and strengths (Fig. 2). The chloride accounts for the supernatant was analyzed for chloride and nearly all the anionic contribution to the total osmotic concentrations. The osmotic and chloride osmotic concentration in the non-regulators and concentrations were determined on the Mechro­ poor regulators with a lesser contribution of the lab vapor pressure osmometer and the Aminco­ chloride ion toward the total osmotic concentra­ Cotlove chloride titrator, respectively. Osmotic tion in the regulators. concentrations were determined against known concentrations of NaCl and are expressed as DISCUSSION milliequivalents of NaCl per liter (meq NaClj1). The results presented here were obtained from animals placed directly into artificially diluted sea water for 24 hours. Inasmuch as such abrupt RESULTS changes in environmental conditions never oc­ The blood osmotic concentrations of the five cur under natural conditions, these results should crab species in varying sea water concentrations not be interpreted as an indication of what oc­ are presented in Figure 1. As is apparent, curs in nature but, rather, as a test of the adapta­ Calappa hepatica has no ability to osmoregulate bility and survivability of these animals under and is an osmoconformer. The blood osmotic such adverse conditions. These data demonstrate, concentration is essentially isosmotic with the then, the ability of these animals to adjust to ambient medium for all sea water concentrations these abrupt changes over a relatively short tested. In 50 per cent sea water, mortality was period of time-an immediate adjustment which approximately 70 per cent in 24 hours. may be critical for the survival of the animal. Rapid and drastic changes in natural salinities, Both Podophthalmus vigil and Portunus san­ however, can occur in estuarine and semiterres­ guinolentus are able to maintain their blood trial environments in which these animals are osmotic concentrations slightly hyperosmotic in found. Strong dilutions of surface waters with 75 and 50 per cent sea water. In 100 per cent consequent mass mortalities of marine organisms sea water, P. sanguinolentus appears to hypo­ have been reported in Kaneohe Bay following osmoregulate. P. vigil is isosmotic to the ambient torrential rains (van Weel and Christofferson, medium in 100 per cent sea water. Mortality was 1966). Under such conditions, survivability of relatively high in 50 per cent sea water in both species. an animal will depend upon its ability to adjust to, or to avoid, these drastically reduced salini­ Thalamita crenata is a good hyperosmoregu­ ties. lator in 50 and 75 per cent sea water and ap­ By regulating the variation of the osmotic proaches isosmoticity in 100 per cent sea water. concentration of its body fluid, an animal can Mortality was relatively low in 50 per cent sea adapt to an external environment in spite of a water. These animals do not survive in 25 per steep osmotic gradient. Two of the decapod spe­ cent sea water. cies studied, Metopograpsus messor and Thala­ Metopograpsus messor is an excellent osmo­ mita crenata, are able to maintain their blood regulator, regulating hyperosmotically in sea osmotic concentrations hyperosmotic to dilute water concentrations below 90 per cent, and sea water concentrations. Portunus sanguinolen­ hypoosmotically above this concentration. The tus and PodophthalmttS vigil also hyperregulate, blood osmotic concentration is maintained at a but poorly, in dilute media. P. sanguinolentlts constant level in 25 to 100 per cent sea water. has some capacity to hyporegulate in 100 per These animals can survive indefinitely in 25 per cent sea water. Its capacity for some degree of cent sea water under the conditions of this ex­ regulation has also been suggested by George periment. (1968), based on his studies of weight changes The chloride concentrations in all crabs in the animals after transfer to dilute sea water. studied follow closely the changes in the blood Calappa hepatica is an osmoconformer, unable 234 PACIFIC SCIENCE, Vol. XXIII, April 1969 to alter its blood osmotic concentration from that The extent to which an animal can survive of the medium. Although data are presented for variations in osmotic concentrations of its body the last three species in 50 per cent sea water, it fluid is limited to the range of osmotic concen­ should be noted that their mortality is high in trations in which the cells can still be functional. this dilute medium. C. hepatica, P. vigil, and P. sanguinolent/Is can 600 500 ... 400 ..... U 0 Z CT CI> E 300 SW 200 L-...--;::2~5---------;:-5~0-------~7~5:---------1~00 PER CENT SEA WATER FIG. 1. Osmotic concentrations of the blood of five crustacean species placed in varying sea water concentra- tions for 24 hours. Each point represents the mean value for ten individuals. 0 0 Calappa hepatica; •• Portunus sanguinolentus; 0 0 Podophthalmus vigil; •• Thalamita crena/a; L:::. L:::. Metopograpsus messor. Sw = sea water. Regulative Capacities of Crustaceans-KAMEMoTo AND KATO 235 tolerate a fairly wide range of osmotic concen­ organic compounds may contribute to the ad­ trations of their blood. No information is avail­ justment of cellular osmotic concentrations in able on the osmotic concentrations of the cells these poor regulators, thus minimizing the in these varying sea water concentrations. It is osmotic effect, as has been proposed by Plorkin possible that osmotic regulation may take place and Schoffeniels (1965). at the cellular level. Free amino acids or other Obviously, most animals are best adapted to 600 500 6 400 ..... ..... I U 0- CIl E 300 SW 2001----;:2:-::5:----------5:="':0::-----------7--5--------1--00 PER CENT SEA WATER FIG. 2. Chloride concentration of the blood of five crustacean species placed in varying sea water concentra- tions for 24 hours. Each point represents the mean value of ten individuals, 0 0 Calappa hepatica; • • POl'tUIIUS sallguillolentus; DD Podophthalmus vigil; • • Thalamita cl'ellata; f:::.