Osmoregulation in Crabs

BIOLOGY 154

Osmoregulation in crabs: The osmoregulators and the osmoconformers

Osmoregulation is an important homeostatic mechanism that regulates an animal’s internal environment. Animals are either osmoregulators or osmoconformers. An osmoconformer’s internal environment is regulated to match the animal’s surroundings. The osmoregulator regulates its internal environment through the loss and uptake of water. It was investigated whether the Cyclograpsus crab species, an intertidal species, and the Plagusia species, an infratidal species, are osmoconformers or osmoregulators. Samples taken from the blood of both species that were exposed to different seawater concentrations were obtained as well as samples of normal seawater, all together there were fourteen samples. The comparative melting-point method was used to determine which species is an osmoconformer and which is an osmoregulator. This method relies on the fact that the greater the ionic concentration of a solution, the lower its melting point. The melting time of the samples of each concentration was obtained. The highest concentrated solutions melted first. The results obtained then showed that the Plagusia crab species is an osmoconformer and the Cyclograpsus species is an osmoregulator. 

Introduction

Osmoregulation is a homeostatic mechanism used to regulate solutes and maintain water loss and gain. Osmoregulatory mechanisms are used to counteract osmotic stress (Amado et al, 2006). Being a homeostatic mechanism, osmoregulation helps to maintain the internal environment of an animal, human or plant. Osmoregulation is based on the movement of solutes between the internal and external environment (Campbell, 2008). In order to achieve this balance there is osmolarity. Osmolarity is the movement of water, determined by the concentration of solutes, across a selectively permeable membrane. These mechanisms have evolved to protect the internal environment of an animal due to changes...