The Shore Crab will also breathe air through its gills. These shore animals are osmoregulators, but most fish respond to oxygen deficiency in shore pools by swimming to offshore waters. Because of the lower temperatures if a cooling system is in operation, it is sometimes possible to increase stocking levels in excess of tropical marines. The pH of natural seawater is 8.3. In aquaria, a figure of 8.0 to 8.3 is acceptable.
Supplements are available to adjust the pH and replace lost salts.
The most obvious response to unfavourable environmental conditions is simply for the animal to move, swim, crawl, or float, to more favourable areas. Fish, crabs, and other mobile animals migrate to and from the coastal pools according to the tides and prevailing conditions. The inter-relationship between the species and their environment is both complex and intresting, with innumerable possibilities. The effect of temperature is both direct, when the water is too hot or too cold, or indirect when the food supply responds to seasonal and temperature variations. Lipophrys pholis inhabiting the warmer offshore waters.