An investigation into the effects of varying seawater concentrations on two marine invertebrates’ osmoregulatory abilities; Carcinus maenas and Arenicola marina.
The concentration of solutes in the bodily fluids of most marine invertebrates is roughly isosmotic to their environment (Raven, 2008). Because there is no osmotic gradient there is no tendency for the net diffusion of water away from the animal’s cells to occur. When a change in salinity occurs some organisms have the ability to maintain a constant internal homeostasis despite these external changes and are known as osmoregulators (Oxford, 2008). Other animals lack this ability and as such are called osmoconformers; their internal osmolarity matches that of their…show more content… Values are mean ± SEM. N=7 for all groups.
As seen in Figure 2 the haemolymph at each concentration closely follows the equivalence line and each reading at the different seawater concentrations is significantly different from every other data point (p<0.001).
Figure 2. Haemolymph chloride levels as a function of seawater chloride at 4 concentrations; 100%, 75%, 50% and 25%. Values are mean ± SEM. N=7 for all groups.
After 3 days in the diluted seawater the crab’s haemolymph Sodium levels were significantly lower (p<0.001) than the crabs stored in full strength seawater as seen in figure 3. There was no significant difference between the mean haemolymph Sodium values of the three dilutions at 75%, 50% and 25%.
Figure 3. Haemolymph Sodium levels as a function of seawater Sodium at 4 concentrations; 100%, 75%, 50% and 25%. Values are mean ± SEM. N=7 for all groups.
There was no significant (p<0.05) difference between the initial weights of the lugworms in the 4 sample groups, avoiding any bias in treatments. As Figure 4 shows each sample group showed a large increase in weight after exposure to the diluted salinities with the lugworms that were placed in full strength seawater not showing an increase of more than 1.7%.
Figure 4. Percentage increase in weight of Arenicola Marina over a period of 90 minutes when exposed to varying dilutions of seawater. Values are mean ± SEM. N=6 for 75%