OSMOREGULATION IN CLAMWORMS - Essay Example

?OSMOREGULATION IN CLAMWORMS Introduction: Neries belongs to the division Annelida and Polychaeta. The worm has 160 segments with well developed setose parapodia. They are the common in tropical and temperate marine habitats. Their native is American Atlantic coasts. They are the large common estuarines. They are also found on the brackish waters. (Oglesby, 1968). Now they are also found at Africa, coastal Europe and Southern Australia. They grow to a height of 190 mm and lives for one year. They reproduce sexually. The most important characteristic of this species is that they are able to withstand the temperature range of 12 - 35°C and survive at a salinity range of 65 ppt for long time and 80 ppt for short time. They are good osmoregulators. Osmoregulation is na active regulation of the osmosis pressure of the body fluids (mainly water) with that of the environmental conditions. Osmosis is maintained both by the terrestrial and marine animals. They do so by excretion through the organs such as kidney and skin. Osmoregulation is of two types, they are osmoregulators and osmo conformers. Osmoregulators are strict regulators of salt and water concentration in the body to that of the environment. osmoconformers match their body fluid concentration to that of the environment.(Masterson, 2008). Neries virens species is able to withstand the salt water content from 5 % to 100%. Some studies have found that they are also able to withstand twice the salt concentration that of salt water. They are only slightly hyperosmotic whereas most of the worms are in osmotic equilibrium with the sea. Review of literature: The body fluids of Nereis are isoosmotic for the sea water. Osmoregulation is one of the important functions of the gut, dorsal pores and the body surface. The salts are transported by active transport and the water by osmosis. Osmosis is the movement of the water (solvent) from high concentration to low concentration across a semi permeable membrane. Here the cell membrane acts as the semi permeable membrane. The influence of the sea water on the weight of the body. The greater the dilution, the greater the increase in the body weight. The worm tends to accommodate itself to the new environment. After the increase in the body weight, they tend to return back to the normal weight if they are left in the original sea water. These euryhaline osmoregulators are thus capable of surviving in reduced, increased salinity levels. They are found to show two types of blood osmo regulation. First they act as hyper osmotic in the diluted sea water with greater osmo regulatory control. Two important mechanisms are stated for this hyper osmotic capability. The transport of the body salts from the body surface to the body fluid through the medium. The second mechanism is by the reduction of the permeability of the body surface to the solutes and solvents. (Oglesby, 1968). For increasing salt concentrations of upto 2 times the salt concentration they act as hypo- osmotic. The concentration of salt in sea water is 1000 m – Osmole / liter and the blood of Nereis contains about 340 – 500 m – Osmole / liter at marine conditions and 280 – 360 m – Osmole / liter at the fresh water levels. The pH of the coelomic fluid was found to increase as the salinity of the water increases. If the salt concentration is higher at the outer environment, the water moves out of the body of the Nereis and thus loses its weight in order to maintain the osmotic pressure as constant. They adapt to the environment very quickly because of the well developed excretory organs. Pronephridia are the excretory and osmoregulaatory organs that are able to drive out the excess water and the waste products. (Whitton, 1975). Another study investigated the osmotic stress due to the long term assimilation and short term assimilation of salinity changes. A single worm was exposed to different salt concentration at different time intervals for a period of 14 days and the changes in weight were measured at continuous time intervals. Another worm was given hyper osmotic shock for short term time interval and the change in the weight of the worm was measured. At low salt concentrations the coelomic fluid osmolality was greater than that of the terrestrial animals. Nereis worm was hyper osmotic at 15% sea water concentration and isoosmotic at 30% sea water concentration. It was also found that the worms in 15% sea water were able to adjust to the new environment within two hours time. For the worm exposed to short term shock, the regulation of the body water concentration was very slower because of the shock. For 30% sea water concentration, the adaptation to the new environment occurred only after 4 days. Thus it was concluded that if the concentration of salt was increased, the adaptability time also got increased due to the osmotic stress. An active transport of the ions was required and the change in the permeability of the cell membrane was also required for the adaptation. (Generelich and Geire, 1996). When the sea water concentration was increased to the actual level in successive series, the Nereis was found to have gained weight. Studies have also found that the volume regulation and the osmosis regulation are found to be associated with the ion concentration. The sodium concentration in Nereis blood was found to be 200-400 mM in the extracellular fluid which is much less compared to the sea water concentration. (Wilmer, Stone and Johnstom, 2000). These changes are acceptable only at the tolerance range. If the environmental conditions exceed the tolerance range then the organisms are not able to control their ion concentration, volume regulation and osmo regulation and hence they create some good compensatory mechanisms. Nereis is the best example for this kind of marine worm. The re-absorption of ions from the urine, control of the haemo lymph composition, efficient anisomotic intracellular regulation (reducing the permeability level of the cell membrane) are adopted by these animals. These adaptation techniques help the animal to spend very less energy for ionic regulation. Short term anoxia and long term anoxia are well tolerated by Nereis. (Baltic Marine Biologists Symposium, 1992). Experimental treatment: In the present study, the Nereis is exposed to three different environmental conditions. The worms are placed in the 50%, 75% and 100% sea water. The 75% sea water condition will act as the control for this study. The worms are blot dried and weighed before the start of the experiment. Three worms are taken and placed in the 50% , 75% and 100% sea water conditions respectively. The worms are weighed at ten minutes time interval for one hour and the weights re recorded. The results are tabulated in the column. Results and discussion: The worm which was exposed to the 50% sea water was found to have increased in the weight. This is due to the hypo osmotic condition that prevailed in the body. The water concentration was higher in the environment and in order to balance with the environment the water molecules moved from the higher concentration to the lower concentration. As Nereis can withstand the very well upto 25% sea water medium, there was no special adaptation mechanism. This resulted in the gradual increase in the water level. Graph 1: the time versus weight chart for the worm present in the 50% sea water concentration. Graph 2: the time versus weight chart for the worm present in the 100% sea water concentration. The worm present in the 100% sea water did not undergo any change in weight during the experiment. It was found to have almost the same weight after one hour. This is due to the maintenance of the osmosis by the worm with the marine environment.Thus it is concluded that the osmoregulation is present in the Nereis worms. References: Baltic Marine Biologists Symposium. (1992). Proceedings of the 12th Baltic Marine Biologists Symposium: physiological and biochemical strategies in Baltic organisms ; new approaches in ecotoxicological research ; changes in Baltic ecosystems, especially those induced by engineering activities, Helsingor, Denmark, 25-30 August 1991, Oslen and Oslen. Generelich, O and Gier, O. (1996). Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids, Hydrobiologia, 334 (1-3): 251- 261. Masterson, J. (2008). Smithsonian Marine station at fort pierce. Retrieved on: http://www.sms.si.edu/irLspec/Neanthes_succinea.htm Oglesby, L. C. (1968). Responses of an Estuarine Population of the Polychaete Nereis Limnicola to Osmotic stress, Biological Bulletin, 134 (1). Whitton, B. A. (1975). River Ecology. University of California Press. Wilmer, P., Stone, G and Johnstom I. A. (2000). Environmental Physiology of Animals. Wiley- Blackwell Press. Read More