Hiding in the Reef
The complex limestone structure of a coral reef provides a huge number of hiding places for prey animals. Unfortunately for them, these hiding places are far from infallible; slender-bodied predators, such as moray eels and whitetip reef sharks, are built for investigating the smallest gaps and crevices in the reef. Whereas some prey fish simply seek safety in numbers as they rest in crowded refuges underneath coral overhangs, other species have adopted remarkable strategies to try to outfox their predators.
Where are the best refuges on the reef?
Given that predators are generally larger than their prey, the best refuges are obviously those that are inaccessible to them. The reef provides plenty of bolt-holes and even the most discerning customer can find a good hiding place. Holes in coral are used extensively by fish such as blennies, some of which gain extra protection by making their home inside stinging fire coral. When they take up residence in a night-time refuge, triggerfish can lock themselves in by clicking their dorsal fin ray into position. And pearlfish actually shelter inside sea cucumbers. This was once thought to be an innocent lodging arrangement, as the fish eats mainly small fish and crustaceans, but more recently it has been suggested that the lodger grazes on its host while hiding within.
Where else can fish hide?
Quite a few fish use the sandy substrate of the seabed in the lagoons or around the reef as an emergency retreat. Wrasses are particularly adept at slicing into the sand, disappearing with a flick of the tail. The razorfish has perfected the same technique, not only to hide but also to hunt for buried invertebrates and small fish, such as garden eels. Sand tilefish build a rubble pile on the seabed, diving into it if danger threatens. Jawfish build burrows tailored exactly to their own body size for this reason. When they sense a predator they retreat into their designer refuge tail-first and may even close off the top with a pebble.
How do parrotfish escape the attentions of nocturnal predators?
Nocturnal predators make extensive use of their sense of smell when locating prey. By sleeping in a cocoon, parrotfishes contain their own chemical signature and prevent it from spreading around the local area and potentially to the noses of predators. Each night the fish spends 20 to 30 minutes manufacturing its mucus cocoon. Once secreted, the mucus becomes firmer, acquiring an almost rubbery texture, and the fish is able to rest within. If a predator does inspect the mucus cocoon, the disturbed parrotfish will shoot out of it, leaving behind the shell, which may serve to distract the hunter just long enough to allow its prey to escape. As well as its anti-predator function, the sac also has anti-bacterial properties that keep the resting fish safe from a host of unpleasant pathogens.