International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 3(10), 38-42, October (2014) Int. Res. J. Environment Sci. International Science Congress Association 38 Effect of Acute Salinity Stress on Oxygen Consumption and Survival of the Fiddler Crab, Uca (Celuca) Lactea Annulipes (Milne- Edwards, 1837) in Different SeasonsMangale Vilas Y. and Kulkarni Balasaheb G.2 1 Mahatma Phule Arts, Science and Commerce College, Panvel, MS, INDIA 2 The Institute of Science, 15, Madam Cama Road, Mumbai, MS, INDIA Available online at: www.isca.in, www.isca.me Received 23th July 2014, revised 26th August 2014, accepted 4th October 2014 AbstractThe present research was undertaken to study the effect of a sudden change in the salinity of the medium on the oxygen consumption and survival of fiddler crab Uca (Celuca) lacteal annulipes from mangrove area of Vashi. Since fiddler crabs are exclusively found in coastal and estuarine habitats in upper intertidal zone, they are subjected to significant fluctuations in salinity during monsoon due to seasonal river input, fresh water runoff and rainfall. The oxygen consumption increased and tolerance levels decreased in dilute seawater. Uca annulipes is a euryhaline where salinity tolerance is found to be season dependent. In monsoon the crabs could tolerate lower salinity of 4.86‰ and survived four days in fresh water. This shows a sort of adaptation to lower salinity during monsoon season. In pre and post monsoon all crabs subjected to fresh water died within a day. In winter they are more susceptible to lower salinity as compared to other seasons. Keywords: Fiddler crab, salinity fluctuations, tolerance, intertidal zone. Introduction Marine animals occupying the intertidal zone are frequently subject to variations in the ambient salinity. Although, salinities are quite constant in the oceans at about 35‰, in coastal and estuarine regions salinity varies from fresh water to full oceanic salinity. Moreover, depending on the geological location salinity varies seasonally due to variation in seasonal river input, fresh water runoff and rainfall. Since fiddler crabs exclusively found in upper intertidal zone, they are subjected to wide fluctuations in salinity, especially at lower salinities. More extreme changes may be temporarily restricted but can ultimately result in the death of organism. The coastal and intertidal organisms adjust to salinity variation in their surrounding by restoring the physiological and biochemical mechanisms present in them. Plenty of research has been carried out to study the effect of salinity fluctuation on the oxygen consumption and physiology of fiddler crabs. Emmerson observed seasonal differences of oxygen consumption in U. urvillei. Miller has studied distribution of the fiddler crabs in relation to salinity2,3. Osmotic and ionic regulation in U. rapax subjected to dilute and hypersaline seawater is studied by Zanders. Thurman have studied osmoregulation in six species of fiddler crabs from different locations differing markedly in salinity. Koch and Gillenhave studied acute physiological and behavioral responses to dilute seawater in U. pugilator . Present study was carried out with the objective of understanding the metabolic responses of fiddler crab, Uca annulipes in response to abrupt salinity changes in the medium. Metabolic response, measured as oxygen consumption of Uca annulipes over time, was studied when the fiddler crabs were exposed to acute change in salinity of the medium. U. annulipes, found abundantly on the shore in and around Mumbai, was selected to find out the effect of change in salinity of the medium on the oxygen consumption and the species’ tolerance to seawater dilution in different seasons. Material and Methods During low tide Uca annulipes were collected at Vashi shore, New Mumbai (1913’00”N 736’30”E). The acclimatized fiddlers, which did not show any mortality, were used for measurement of oxygen uptake after exposing them to different salinity viz. 0.32 ‰, 4.86 ‰, 9.61 ‰, 16.02 ‰, 22.43 ‰, and 32.04 ‰. Seawater dilutions were prepared by adding distilled water to local seawater of salinity 32.04 ‰. Experimental setup consisted of covered glass tanks each with fifteen fiddler crabs and equal volume (4 liters) of seawater of different experimental salinity. The water was aerated continuously and changed every 24 hours to prevent the build-up of toxic wastes. Experiments were carried out in duplicate. The crabs were checked for survival every 60 minutes for the first 12 hours and then at 24 hour intervals for 30 days. Measurement of initial oxygen consumption as well as after the exposure period of four days and again after one month was carried out. The acute response of oxygen consumption to salinity change was measured in all the experimental salinities. The experiment was repeated in three season viz. pre monsoon, monsoon and post monsoon. International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(10), 38-42, October (2014) Int. Res. J. Environment Sci. International Science Congress Association 39 For measuring oxygen uptake, initial oxygen content of sea water of different salinities was estimated by Winkler’s method. Wide mouthed amber coloured bottles each with a capacity of one liter were filled with seawater of different salinities and then four weighed fiddler crabs were placed in each bottle. The bottles were made airtight by rubber corks and then sealed carefully with molten wax. These bottles were kept undisturbed at room temperature for 1 hour. After one hour, the water from these bottles was siphoned out carefully into BOD bottles of capacity 300 ml each and the oxygen content was estimated by Winkler’s method . The rate of oxygen consumption of fiddler crab was determined by taking the difference between initial oxygen content and final oxygen content obtained after the exposure of the crab for one hour. Results were expressed as oxygen consumed per gm. of body weight per hour. Results and Discussion Effect of salinity variation on survival: It is found that tolerance of the Uca annulipes to salinity variation is season dependent. When the crabs were exposed to lower salinities like 9.61‰ and 16.02‰ in monsoon season, mortality was not recorded. During monsoon, the crabs were found to survive in water with salinity 0.32‰ for more than 4 days. However, in pre and post monsoon 100% mortality of the crabs was noted after their exposure to water with salinity 0.32‰ during four days. Seasonal variation of oxygen consumption: A variation in respiratory rate is evident in Uca annulipes as shown in table No.1. The data therein shows that in post monsoon lowest rate of oxygen consumption i.e. 0.124 ± 0.02 ml/gm/hr was noted and crabs were found inactive mostly in early morning. A highest rate of 0.176 ± 0.01 ml/gm/hr was noted in monsoon. In pre monsoon oxygen consumption was 0.171 ± 0.01 ml/gm/hr. Table–1 Seasonal variation in oxygen consumption of Uca annulipesValues are mean (± SD) of 3 determinations. Values in parenthesis indicate range Season Oxygen Consumption ml/gm/hr Pre monsoon 0.19 ± 0.01 (0.18 – 0.21) Monsoon 0.16 ± 0.01 (0.15 – 0.17) Post monsoon 0.14 ± 0.02 (0.12 – 0.16) Effect of salinity variation on oxygen consumption in different seasons: The data presented in table nos. 2 to 4 and figure no. 1 shows that lower salinity affects oxygen consumption remarkably in Uca annulipes in all the three seasons. When the crabs were exposed to lower salinity of 4.86‰, a significant increase in oxygen consumption was noted after 4 days of exposure in all the three seasons. However, in pre and post monsoon season, a remarkable elevation in oxygen consumption was noted after 4 hours of exposure. The crabs would not tolerate lower salinity water (0.32‰) beyond 4 hours and 100 % mortality of the crab was noted in pre and post monsoon season. In monsoon season it was found that crabs survived in the salinity of 0.32‰ for four days. Table – 2 Effect of salinity variation on oxygen consumption of Uca annulipes in pre monsoon Values are mean (± SD) of 3 determinations. Values in parenthesis indicate range Sea Water (Salinity) Exposure period Oxygen consumption (ml/gm/hr) 0.32‰Initial 0.187± 0.002 (0.185 – 0.189) 4 Hours 0.248 ± 0.002 (0.248 – 0.250) 30 Days ------------------ 4.86‰Initial 0.180 ± 0.002 (0.178 – 0.181) 4 Days 0.241± 0.002 (0.239 – 0.242) 30 Days 0.184 ± 0.004 (0.179 – 0.187) 9.612‰Initial 0.175 ± 0.001(0.174 – 0.176) 4 Days 0.231 ± 0.002 (0.230 – 0.233) 30 Days 0.179± 0.002 (0.177 – 0.181) 16.02‰Initial 0.174 ± 0.002 (0.172 – 0.176) 4 Days 0.186 ± 0.003 (0.183 – 0.189) 30 Days 0.176 ± 0.001(0.175 – 0.177) 22.43‰Initial 0.171 ± 0.002 (0.169 – 0.173) 4 Days 0.168 ± 0.005 (0.163 – 0.172) 30 Days 0.172 ± 0.002 (0.171 – 0.174) 32.04‰Initial 0.172 ± 0.006 (0.165 – 0.177) 4 Days 0.176 ± 0.002 (0.174 – 0.177) 30 Days 0.171 ± 0.002 (0.169 – 0.172) International Research Journal of Environment Vol. 3(10), 38-42, October (2014) International Science Congress Association Table–3 Effect of salinity variation on oxygen consumption of annulipes in monsoon. Values are mean (± SD) of 3 determinations. Value s in parenthesis indicate range Sea Water (Salinity) Exposure period Oxygen consumption (ml/gm/hr) 0.32‰Initial 0.186 ± 0.001 (0.185 4 Days 0.204 ± 0.002 (0.202 30 Days ---------------------- 4.86‰Initial 0.177 ± 0.001 (0.176 4 Days 0.187 ± 0.003 (0.185 30 Days 0.186 ± 0.003 (0.183 9.612‰Initial 0.176 ± 0.000 (0.176 4 Days 0.182 ± 0.002 (0.181 30 Days 0.177 ± 0.002 (0.175 16.02‰Initial 0.172 ± 0.001 (0.171 4 Days 0.178 ± 0.003 (0.175 30 Days 0.176 ± 0.001 (0.175 22.43‰Initial 0.170 ± 0.001 (0.179 4Days 0.171 ± 0.002 (0.169 30 Days 0.173 ± 0.002 (0.171 32.04‰Initial 0.174 ± 0.002 (0.173 4 Days 0.175 ± 0.002 (0.173 30 Days 0.174 ± 0.002 (0.173 Effect of salinity variation on oxygen consumption (ml/gm/hr) in Environment Sciences_______________ _________________________ International Science Congress Association Effect of salinity variation on oxygen consumption of Uca Values are mean (± SD) of 3 s in parenthesis indicate range Oxygen consumption (ml/gm/hr) 0.186 ± 0.001 (0.185 – 0.187) 0.204 ± 0.002 (0.202 – 0.205) ---------------------- 0.177 ± 0.001 (0.176 – 0.177) 0.187 ± 0.003 (0.185 – 0.190) 0.186 ± 0.003 (0.183 – 0.188) 0.176 ± 0.000 (0.176 – 0.176) 0.182 ± 0.002 (0.181 – 0.184) 0.177 ± 0.002 (0.175 – 0.179) 0.172 ± 0.001 (0.171 – 0.173) 0.178 ± 0.003 (0.175 – 0.180) 0.176 ± 0.001 (0.175 – 0.177) 0.170 ± 0.001 (0.179 – 0.170) 0.171 ± 0.002 (0.169 – 0.172) 0.173 ± 0.002 (0.171 – 0.174) ± 0.002 (0.173 – 0.176) 0.175 ± 0.002 (0.173 – 0.176) 0.174 ± 0.002 (0.173 – 0.176) Table– 4 Effect of salinity variation on oxygen consumption of annulipes in post monsoon, Values are mean (± SD) of 3 determinations. Values in parenthesis indicate range Sea water (Salinity) Exposure period 0.32‰Initial 0.178 ± 0.001 (0.178 4 Hours 0.224 ± 0.001 (0.223 30 Days 4.86‰Initial 0.166 ± 0.001 (0.165 4 Days 0.202 ± 0.003 (0.198 30 Days 9.612‰Initial 0.145 ± 0.001 (0.144 4 Days 0.192 ± 0.002 (0.190 30 Days 0.147 ± 0.002 (0.146 16.02‰Initial 0.128 ± 0.001 (0.127 4 Days 0.171 ± 30 Days 0.136 ± 0.003 (0.133 22.43‰Initial 0.122 ± 0.002 (0.121 4 Days 0.127 ± 0.002 (0.125 30 Days 0.131 ± 0.003 (0.129 32.04‰Initial 0.122 ± 0.002 (0.120 4 Days 0.119 ± 30 Days 0.124 ± 0.002 (0.122 Figure-1 Effect of salinity variation on oxygen consumption (ml/gm/hr) in Uca annulipes in various seasons _________________________ ______ ISSN 2319–1414 Int. Res. J. Environment Sci. 40 4 Effect of salinity variation on oxygen consumption of Uca Values are mean (± SD) of 3 parenthesis indicate range Oxygen consumption (ml/gm/hr) 0.178 ± 0.001 (0.178 – 0.179) 0.224 ± 0.001 (0.223 – 0.225) ---------------- 0.166 ± 0.001 (0.165 – 0.167) 0.202 ± 0.003 (0.198 – 0.204) ------------ 0.145 ± 0.001 (0.144 – 0.146) 0.192 ± 0.002 (0.190 – 0.193) 0.147 ± 0.002 (0.146 – 0.149) 0.128 ± 0.001 (0.127 – 0.128) 0.171 ± 0.002 (0.169 – 0.173) 0.136 ± 0.003 (0.133 – 0.139) 0.122 ± 0.002 (0.121 – 0.124) 0.127 ± 0.002 (0.125 – 0.129) 0.131 ± 0.003 (0.129 – 0.134) 0.122 ± 0.002 (0.120 – 0.124) 0.119 ± 0.002 (0.117 – 0.121) 0.124 ± 0.002 (0.122 – 0.125) in various seasons International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(10), 38-42, October (2014) Int. Res. J. Environment Sci. International Science Congress Association 41 When crabs were exposed to salinity of 4.86‰, 9.61‰ and 16.02‰, increase in oxygen consumption was noted after 4 days of exposure in all the three seasons. Maximum elevation of 65.57 % was noted in the crabs after exposure to salinity of 4.86‰ in post monsoon. The crabs could not tolerate salinity of 4.86‰ in post monsoon beyond 4 days of exposure. In sea water with lower salinities, the oxygen consumption was found to be elevated during 4 days of exposure. However, it was found to be decreased again after 30 days of exposure. In sea water with salinity 9.61‰ and 16.02‰, oxygen consumption after 30 days of exposure was found to be normalized showing slight elevation as compared to the initial oxygen consumption in respective saline water. Water with salinity 22.43‰ shows a significant increase in oxygen consumption in post monsoon season. However, in pre monsoon a variation in oxygen consumption after 4 and 30 days found to be insignificant. Similar trend of oxygen consumption was noted in salinity of 22.43‰ in monsoon. At normal salinity of 32.04 ‰ in all three season, oxygen consumption showed slight variation with respect to initial values. Figure 1 shows the effect of salinity variation in different seasons on oxygen consumption of fiddler crabs. The oxygen consumption was found to be increased during four days of exposure to low salinity. But the consumption decreased to initial level after thirty days. This shows an adaptation in changed salinity after prolonged exposure. The observed differences in survival of U. annulipes at various salinities in different seasons can be attributed to the acclimatization of the crabs to a particular salinity regime in particular season. Further, distribution of U. annulipes at upper zone of intertidal region is also responsible for their survival at lower salinities during different seasons. It was observed that the area inhabited by U. annulipes gets flooded with freshwater during monsoon which results in decrease of salinity in the surroundings of the crabs. Presence of low saline water in the surroundings of the crab leads to acclimatization of the crabs to lower salinity. Therefore, it was noted that during monsoon period crabs could tolerate salinity of 0.32‰ for the period of four days under laboratory conditions. However, during pre and post monsoon the crabs could not survive beyond twenty four hours at salinity of 0.32‰. Further, low survival rate in winter at salinity of 4.86‰ can be attributed to the effect of low salinity and low temperature in the surroundings of the crab. Miller has studied distribution of the fiddler crabs in relation to salinity. Some investigators have studied the effect of salinity on the metabolic rate of crustaceans 7-11. Salinity is one of the main environmental factors disturbing the metabolism of intertidal organisms12. Organisms living in an environment with fluctuating salinity levels have to cope with substantial ionic and osmotic stress, either through active osmoregulation or by osmoconforming. Oxygen consumption rates can be used to evaluate the amount of energy an organism is using to maintain a stable concentration of the internal fluids13. The results reported here show increase in the oxygen consumption of U. annulipes when exposed to dilute seawater, a response seen commonly in previous studies. Rao has suggested that the rate of oxygen consumption of many species of crustaceans depends on the salinity of the medium to which the animals are naturally adapted. He showed that the oxygen consumption rate increased with increased differences in osmotic concentration between the blood of the prawn and the external medium. Many investigators have shown that the respiratory rate increases as salinity decreases14-17 Several theories have been formulated to explain this increase in respiratory rate in low salinities. In low salinities, however, there would be a tendency for carbon dioxide to accumulate, thus increasing respiratory rate. Lange proposed that the increased solubility at lower salinity, coupled with oxygen-dependent respiration, is responsible for enhanced oxygen consumption at lower salinity 13. The most commonly proposed theory is that the increased metabolic rate is caused by increased osmotic work 15,18,19. In present investigation it was recorded that low saline acclimated U. annulipes showed lower respiratory rates in midrange salinities (16‰ and 22‰) and higher respiratory rates in low (0.5‰, 5‰ and 10‰) salinities. Such characteristic responses to salinity have been reported for various crustaceans9-21. It has been shown that in euryhaline crustaceans, maintenance of a hyper osmotic extracellular fluid in low salinities requires the expenditure of energy22. Hyperosmoregulation in low salinities relies on the ability to absorb ions against a concentration gradient, which involves expenditure of energy. Other predominant energy consuming phenomena operating in low saline media are reported to be an increase in oxidative deamination of free amino acids 21. Conclusion Uca annulipes shows seasonal dependent salinity tolerance. In monsoon the crabs could tolerate lower salinity of 4.86‰ and survived four days in fresh water. This shows a sort of adaptation to lower salinity during monsoon season. In pre and post monsoon all crabs subjected to fresh water died within a day. In winter they are more susceptible to lower salinity as compared to other seasons. 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