Lake Erie, a prominent freshwater body, is often a subject of curiosity regarding its inhabitants. While the term “crab” typically conjures images of marine environments, true marine crabs do not reside in Lake Erie. This significant freshwater ecosystem, however, supports a diverse array of other crustaceans.
Why True Crabs Aren’t in Lake Erie
True crabs belong to the order Decapoda. These crustaceans are characterized by a short, broad body with an abdomen typically tucked beneath their thorax. While decapods, including crabs, lobsters, and crayfish, generally possess five pairs of legs, true crabs are predominantly found in marine or estuarine habitats.
The primary reason for their absence in freshwater environments like Lake Erie is osmoregulation. Marine crabs have internal body fluids with a salt concentration similar to seawater. In freshwater, water rushes into their bodies via osmosis, overwhelming their system and causing cells to swell. Simultaneously, vital salts are lost, disrupting crucial bodily functions. Most marine crabs cannot efficiently regulate this balance and typically die, while freshwater crustaceans have evolved specialized mechanisms to maintain their internal balance.
What Crustaceans Call Lake Erie Home
Although true crabs are not native to Lake Erie, many other crustaceans, some often mistaken for crabs, successfully inhabit its waters. Crayfish are a common example, sharing the Decapoda order with crabs but being distinctly adapted to freshwater. Among native species, the Northern Clearwing Crayfish (Faxonius propinquus) is found in the region.
An invasive species, the Rusty Crayfish (Faxonius rusticus), has significantly impacted Lake Erie’s ecosystem. Originally from the Ohio River basin, this aggressive species out-competes native crayfish for food and shelter. Rusty Crayfish can reduce the diversity of other macroinvertebrates, including snails, insects, and amphipods, and are known to consume fish eggs and damage aquatic vegetation, altering the lake’s food web.
Beyond crayfish, Lake Erie hosts numerous smaller crustaceans that play fundamental roles in the aquatic food web. Amphipods, often called scuds, are small, laterally compressed crustaceans that serve as an important food source for various aquatic organisms. The native amphipod Gammarus fasciatus is present, though it faces competition from the invasive Echinogammarus ischnus, which has displaced native populations in some areas.
Copepods are microscopic crustaceans crucial to the lake’s food chain, serving as a primary food source for many larval and juvenile fish. Lake Erie’s copepod community includes both carnivorous cyclopoid copepods, such as Cyclops bicuspidatus, and omnivorous calanoid copepods like Diaptomus spp. Cladocerans, or water fleas, are another group of tiny crustaceans, with Daphnia retrocurva being a common species in the lake, alongside Daphnia galeata. These filter-feeding organisms, including Ceriodaphnia species, are vital for controlling phytoplankton and transferring energy through the food web.
While not established, the Chinese mitten crab (Eriocheir sinensis) represents a potential invasive threat to the Great Lakes, including Lake Erie. This species, native to Asia, can tolerate a wide range of salinities and spends most of its life in freshwater, though it requires saltwater for reproduction. Individual specimens have been collected in Lake Erie as early as 1965 and as recently as 2007, but there is currently no evidence of an established, reproducing population in the Great Lakes. The Chinese mitten crab poses risks due to its burrowing habits, which can cause river bank erosion, and its potential to consume fish eggs and compete with native species.