Polluted estuaries are great for crabs...

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The phrase, “location, location location” is not only applicable to determining the desirability of a property, it is also useful advice to some crustaceans living in estuaries.

A paper published in a recent issue of the journal BioScience has found that crustaceans living in polluted estuaries tend to grow larger because of reduced pressure from predators.  

Focusing on five species, Judith Weiss and three of her graduate students studied the feeding behaviour and predator-prey relations in contaminated and clean estuaries and examined the population and community-level consequences.  

The contaminated sites that they studied in northern New Jersey are part of the highly urbanised New York-New Jersey Harbour estuary system and display high levels of PCBs (polychlorinated biphenyls), dioxins and metals, among other pollutants.

The five species that the authors focused on are the Common killifish (Fundulus heteroclitus), young Bluefish (Pomatomus saltatrix), Grass shrimp (Palaemonetes pugio), Fiddler crabs (Uca pugnax) and Blue crabs (Callinectes sapidus).

The results of their studies, which were reviewed in this paper, showed that the predators (primarily the fishes) are more adversely affected by contaminants than their prey (primarily the crustaceans). For instance, the authors found that both species of fishes ate less in the polluted estuaries, with the killifish and the Bluefish showing reduced growth as a result.

The fishes living in the polluted estuaries also showed considerable behavioural changes, being poorer predators overall and less likely to successfully escape from other organisms that eat them.

Partly as a result of the reduced predation pressure from the fishes, the authors found that the crustaceans fared better: the Grass shrimp were more numerous and larger, and both the Fiddler and Blue crabs also grew to larger sizes.

The Fiddler crabs were found to be more sedentary and spend more time in burrows when living in a polluted environment. This may have contributed to their larger size, as they were less likely to be eaten by predators (Blue crabs) when they spend more time hidden.

Although the Blue crabs living in the polluted estuaries were less capable of catching small fishes, crabs and molluscs to eat, they compensated for this by eating more algae and detritus. They also reached larger sizes by living longer. This is due to reduced predation pressure from humans (who are forbidden to catch them in polluted waters by law).

For more information, see the paper: Weis, JS, L Bergey, J Reichmuth and A Candelmo (2011) Living in a contaminated estuary: behavioral changes and ecological consequences for five species. BioScience 61, pp. 375–385

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