Sand fleas are widespread crustaceans found on sandy coastlines globally. These small, barrel-shaped invertebrates are adept burrowers, quickly burying themselves tail-first in the wet sand of the intertidal zone, particularly in the swash zone where waves break. As filter feeders, they use their feathery antennae to capture plankton and detritus from the receding waves. This behavior makes them a readily available food source for various marine animals, establishing their importance in coastal ecosystems.
Fish Species That Prey on Sand Fleas
Many fish species feed on sand fleas, making these crustaceans an important part of their diet. Surfperch, like the Barred Surfperch, are prominent predators, with sand fleas sometimes constituting a large majority of their diet. These fish inhabit the surf zones of sandy beaches, where sand fleas are most abundant. California corbina, a type of croaker, also extensively prey on sand fleas. They are commonly found along sandy surf-swept beaches and in shallow bays, often feeding in water so shallow that their backs become exposed.
Croakers, including the Yellowfin Croaker, also rely on sand fleas. Their diet primarily consists of small crustaceans, along with mollusks and marine worms, as they forage on sandy bottoms in the surf zone. Rays, such as the Bat Ray, also consume sand fleas as part of their diverse diet of mollusks and crustaceans. Bat rays are bottom dwellers, inhabiting muddy or sandy sloughs, estuaries, and bays, where they can easily access buried prey.
How Fish Hunt Sand Fleas
Fish employ various sensory and behavioral adaptations to locate and capture sand fleas buried in the sand. Many species use their lateral line system, a network of sensory organs along their body, to detect subtle movements and pressure changes in the water. This system allows them to sense vibrations created by sand fleas as they burrow or emerge. In clear water, sight also helps identify areas where sand fleas are present, especially visible “V”-shaped ripples in the sand created by their feeding antennae.
Once a fish detects sand fleas, they engage in specific hunting behaviors. Many fish, like California corbina, root around in the sand, scooping up mouthfuls of substrate. They then sift the sand through their gill openings, retaining the sand fleas and expelling the sand. Bat rays use their wing-like pectoral fins to flap and move sand, exposing hidden prey, and may use their snouts to dig trenches. Some fish may ambush sand fleas as they briefly emerge from the sand with the incoming or receding tide.
Sand Fleas’ Role in the Coastal Food Web
Sand fleas hold an important position within the coastal food web, linking microscopic organisms and larger predators. As filter feeders, they consume plankton and detritus from the water, transferring energy from lower trophic levels into the food chain. Their abundance and widespread presence on sandy beaches make them a consistently available, calorie-rich food source for many species.
This availability directly influences the health and distribution of predator populations, including the fish species that depend on them. Fluctuations in sand flea populations can impact the feeding success and well-being of surfperch, corbina, croakers, and rays. Sand fleas are not merely prey items but are important components that support the energetic flow and ecological balance of dynamic coastal environments.