Crabs and lobsters are familiar inhabitants of marine and freshwater environments, representing two large groups of crustaceans known as decapods. Their name, meaning “ten feet,” refers to the five pairs of legs they possess, including their prominent claws. These hard-shelled organisms play a significant role in the balance of their ecosystems. Understanding their diet reveals how these animals contribute to the cycling of nutrients and the structure of aquatic communities.
General Feeding Habits: Scavengers and Predators
Crabs and lobsters are broadly classified as opportunistic omnivores, and they readily consume whatever is available in their habitat. Their feeding behavior generally falls into two categories: scavenging and predation. Scavenging involves consuming dead or decaying organic matter, such as carrion, detritus, and marine snow.
Predation involves actively hunting and capturing live prey. The degree to which a species scavenges or preys depends heavily on its specific environment, body size, and the food resources present. Most species are highly adaptable, switching between roles based on necessity. This flexibility ensures their survival across diverse aquatic landscapes.
The Diverse Diet of Crabs
The diet of crabs is remarkably varied. A large portion of many crab diets consists of detritus and organic waste, which they process by sifting through sand or mud. For example, fiddler crabs use their smaller claws to pick up sediment and extract microscopic organic particles and bacteria.
Larger crab species, such as the Atlantic blue crab and the Dungeness crab, are more active predators with a broader menu. They consume small invertebrates like worms, mollusks, and crustaceans. Blue crabs are known to actively hunt small fish and crack open the shells of clams and mussels using their powerful claws. Certain crabs, like the mottled crab, are specialist herbivores, feeding on various forms of algae and plant matter.
In some specialized species, feeding involves filtering microscopic food from the water column. Porcelain crabs, for instance, use specialized, feathery mouthparts to strain plankton from the surrounding seawater. This wide range of feeding strategies underscores the diversity of the crab group, with diets ranging from nearly pure detritus to active carnivory.
The Predatory Diet of Lobsters
Lobsters generally lean more toward active predation compared to many crab species, but they remain opportunistic feeders. Their primary diet consists of slow-moving benthic invertebrates. This prey includes a variety of hard-shelled animals such as clams, mussels, sea urchins, and snails. Lobsters also pursue and consume small fish and other crustaceans, including smaller or recently molted crabs.
The American lobster, a clawed species found in cold waters, is a strong hunter that uses its powerful appendages to access food. Spiny lobsters, common in warmer waters, lack the large crushing claws of their American counterparts, which influences their diet. While they still eat mollusks and worms, their feeding often involves more scavenging of detritus and macroalgae compared to the American lobster’s focus on actively breaking open thick shells. Lobsters will readily scavenge for fresh carrion when available.
Physical Adaptations for Feeding
The primary tools for food acquisition and processing in both crabs and lobsters are their chelae. Clawed lobsters and many crabs possess two distinct types of claws: the crusher claw and the pincer or cutter claw. The crusher claw is typically larger and blunter, generating the force necessary for breaking open the shells of clams, mussels, and sea urchins.
The pincer claw is sharper and more slender, functioning to grasp, tear, and hold softer prey items. Once food is captured and torn into manageable pieces, it is passed to the mouthparts, which are complex, modified appendages. These mouthparts include mandibles and maxillipeds, which work together to further shred and manipulate the food before it is ingested. The final stage of physical digestion occurs internally, as the food is ground up by a structure known as the gastric mill.