7. Hermit Crabs and Their Living Shells: A Mobile Home for Sea Anemones
In coral reef environments, hermit crabs and some species of sea anemones have an amazing symbiotic relationship—a movable collaboration. Renowned for their use of abandoned shells as protected shelters, hermit crabs extend this behaviour to include forging friendships with sea anemones. Growing and changing its shell, the hermit crab gently moves its anemone mate to her new habitat. Both those engaged in this partnership stand to gain greatly. Attachment to the shell of the hermit crab gives the sea anemone a mobility platform that lets it reach more food sources than it would if it were fixed. The crab’s foraging activity increases the feeding chances by bringing the anemone into touch with different food particles in the water. The mobility also helps the anemone avoid areas of low water quality or too much sedimentation that would endanger its health. In turn, the hermit crab gets greater defence. The stinging tentacles of the anemone discourage predators that may otherwise attack the crab, therefore providing a living shield. Some hermit crabs even employ the anemones as weapons, running off attackers with their claws. Some hermit crab species have evolved specialised limbs especially for clinging to their anemone mates since this cooperation is so helpful. Hermit crabs and sea anemones exhibit the complex and sometimes unexpected ways in which many species may come to depend on one another in the marine environment, therefore highlighting the rich web of life seen within coral reef systems.