8. Trapezia Crabs and Their Coral Hosts: Tiny Guardians of the Reef
One of the best examples of how little animals could be quite important in preserving the condition of bigger reef systems is the symbiotic link between Trapezia crabs and their coral hosts. Often barely more than a fingernail, these small crabs live in the branches of pocilloporid corals. Although at first look the crabs seem to be just using the structure of the coral for cover, the interaction is significantly more complicated and mutually beneficial. For their coral hosts, the Trapezia crabs are relentless protectors offering many essential functions. First they actively protect the coral from predators, especially the ravenous crown-of- thorns starfish that may wipe out whole coral colonies. Often at great danger to themselves, the crabs battle off these invaders with their keen claws. By clearing silt and trash that settles on the surface of the coral, the crabs also help to maintain it clean. The health of the coral depends on this cleaning service since it helps to avoid the buildup of elements that can smother the coral polyps or restrict their capacity to feed. By excreting waste materials the coral may use, the crabs also add to its nourishment. The coral gives the crabs a safe habitat and a consistent supply of food—mucus and trapped organic matter—in exchange for these services. Corals harbouring Trapezia crabs have been demonstrated to have superior overall health and higher survival rates than those without crab mates due to this very significant association. The Trapezia crab-coral symbiosis emphasises the need of maintaining these complex interactions in conservation activities since it shows how even little animals may have a major influence on the resilience and health of coral reef ecosystems.