The European green crab, Carcinus maenas, is a successful invasive species impacting coastal ecosystems globally. Originating from the North-east Atlantic Ocean and Baltic Sea, this crab has spread extensively, establishing populations across North America’s Atlantic and Pacific coasts, South Africa, Australia, South America, and parts of Asia. Their adaptability and versatile diet contribute to their ecological footprint in these new environments.
Diverse Dietary Habits
Green crabs are generalist, opportunistic predators. They consume a wide range of available food sources. Their feeding strategies involve using strong claws to crush prey shells and burrowing into sediments to uncover hidden organisms. They also engage in scavenging, consuming detritus and dead organisms.
Several factors influence a green crab’s diet, including its size, age, habitat, and prey availability. These crabs are primarily active during the night and at high tide, when prey is more accessible. In challenging conditions, green crabs show adaptability, even absorbing dissolved nutrients directly through their gills.
Key Prey Species
Green crabs consume a diverse array of marine organisms, impacting various species within coastal food webs. Mollusks form a significant portion of their diet, including commercially important species such as soft-shell clams, blue mussels, oysters, and bay scallops. They also prey on other mollusks like whelks, chitons, periwinkles, quahogs, and dogwhelks.
Beyond mollusks, green crabs consume other crustaceans, including smaller crabs (even juvenile green crabs, demonstrating cannibalism), shrimp, and various barnacles. Polychaete worms are another frequent food item, including Hediste diversicolor and tubeworms. Small fish, particularly juvenile and benthic species, are also part of their diet. While primarily carnivorous, green crabs supplement their diet with plant matter, consuming algae and general detritus, especially when other food sources are scarce.
Ecological Impacts of Predation
The predatory activities of green crabs have consequences for native ecosystems. Their consumption of native species can lead to declines in populations, particularly affecting local shellfish such as clams and oysters, which impacts commercial fisheries. This predation pressure can also lead to a loss of biodiversity within invaded habitats.
Green crabs often outcompete native predators for food resources, disrupting established food webs and further stressing native species. They can outcompete native Dungeness crabs and prey heavily on smaller native shore crabs. Beyond direct predation, their feeding and burrowing activities can physically alter habitats, disturbing sediments and damaging eelgrass beds and salt marshes. These combined impacts contribute to ecological shifts in the regions they invade.