Brittle stars (class Ophiuroidea) are diverse marine invertebrates, closely related to sea stars, found globally from shallow coastal waters to the deep sea. They are highly abundant, often forming dense aggregations on the seafloor, and contribute to the health of benthic ecosystems. As common and widespread inhabitants, brittle stars frequently serve as a food source for various marine animals.
Marine Predators of Brittle Stars
Fish are frequent predators, with species like cod, haddock, and various flatfish consuming them. Wrasses, triggerfish, angelfish, and hawkfish also prey on brittle stars.
Crustaceans are another significant group of predators. Crabs, including rock crabs, spider crabs, hermit crabs, and emerald crabs, use their powerful claws to break apart and consume brittle stars. Lobsters and mantis shrimp also feed on them.
Other echinoderms, such as sea stars (e.g., common starfish, spiny starfish), prey on brittle stars, and larger brittle stars can exhibit cannibalistic tendencies. Less common predators include gastropods, certain shrimp, octopuses, and opportunistically, some seabirds, sea turtles, and otters. Brittle stars are a suitable food source for many of these animals due to their abundance, relatively small size, and often exposed habitats.
Hunting Tactics of Brittle Star Eaters
Predators employ various strategies to capture and consume brittle stars. Many fish species, particularly bottom dwellers, use suction feeding to engulf brittle stars or actively forage for them within the sediment. Wrasses, for instance, slurp brittle stars from hiding spots. Ambush predators like hawkfish lie in wait to seize any brittle star that ventures too close.
Crabs and lobsters use their strong chelipeds (claws) to crush brittle stars’ bodies and tear off their arms, allowing them to access softer tissues. Predatory sea stars often evert their stomachs over a captured brittle star, releasing digestive enzymes to break down the prey externally; smaller brittle stars may be engulfed whole. Octopuses, though not primary predators, use their flexible arms to manipulate and bring captured brittle stars to their beaks for consumption.
Brittle Star Defenses
Brittle stars have developed several ways to protect themselves from predators. A key defense mechanism is autotomy, the ability to voluntarily detach one or more arms when threatened. The severed arm may continue to wriggle, creating a distraction that allows the brittle star to escape. Lost arms can then regenerate over a period of weeks to months. This self-amputation occurs at specific fracture points along the arm.
Many brittle star species exhibit nocturnal activity, hiding during the day to avoid visually-oriented predators like fish. They often seek refuge by burrowing into soft sediments or tucking themselves into crevices and under rocks. Some species use cryptic coloration, blending with their surroundings such as sand, rocks, or coral, to avoid detection. Additionally, over 60 species of brittle stars are bioluminescent, producing light that may deter predators through a startle effect, act as a sacrificial lure by illuminating a detached arm, or function as a “burglar alarm” to attract a predator’s own predators. Some brittle stars also produce chemical deterrents and can detect chemical cues from approaching threats.