Crabs in the Estuary

Crabs in the Estuary
By Barbara Ducote
Fall 97

The order Decapoda contains some of the most highly specialized crustaceans. This order contains over one third of the known crustacean species. Included in this group are shrimp, crayfish, lobsters, and crabs.

The development of the crab has been an interesting evolutionary process. The adaptations that have evolved to be the crab have been basic for locomotion or habitat.

The abdomen of crabs is greatly reduced when compared to other crustaceans. The abdomen fits tightly beneath the cephalothorax. With the attachment of appendages, this gives the crab a unique appearance. Crabs can crawl forward slowly but commonly move in a sideways motion. This gives them a very comical appearance. Most crabs can not swim in the true sense but they are able to run at rapid rates.

Crabs exhibit a wide range of feeding habits such as herbivorous and scavenging tendencies. Their food source is caught or picked up with the chelipeds or specialized front claws and then passed to the maxillipeds and into the mouth. The size and shape of the chelipeds reflects the feeding habits of the particular species of crab. Crabs, which have a diet of algae, have a spooned shaped claw. This allows them to scoop up or scrap algae off of the bottom or rocks. Those with a diet of shellfish have heavy claws with blunt teeth. This allows them to catch their prey and crack their shells. The crabs that are scavengers have shape pincers, which allows them to tear apart their food. The filer feeders have claws which and scoop up mud and other bottom materials.

Crabs appear to go through an extensive courtship behavior before mating. Pheromones are important in sexual attraction. In tropical species courting appears to take place in daylight hours and reaches a peak at the time of low tide. Males may attract females by waving their claws. The male entices the female to his burrow by rapping at the opening. Once the female enters the burrow matting is completed. In many species the female remains in the burrow to lay the eggs.

Crabs are a necessary part of the estuary system. Their scavenging tendencies help to keep the estuary form becoming polluted. They are an important part of the food chain. It is because of the crabs that the estuary system is able to maintain is balance.

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