HOW DOES A WHALE BECOME A REEF?
There is hardly any other mammal that looks as furrowed, scarred, and generally afflicted as a humpback whale: The picture at right is of a female whale’s head, photographed from the front. Her skin is covered with ugly scars, barnacles, and other parasites, and it looks as though she could hardly open her mouth, seen here as a narrow line toward the top of her head. In fact, there have been instances in which parasites have come close to closing off the blowhole of a weakened animal, threatening its ability to breathe. But in general, even half a ton of the kind of yellowish barnacles seen glimmering in this image would not bother a humpback whale, which can weigh around 30 tons itself. Proportionally, the barnacles weigh only about as much as clothes do on us. And strictly speaking, the relationship is actually commensal: The barnacles benefit from a whale without helping or harming it. It’s the barnacles’ version of meals on wheels, and they get to ride along for the delivery. Both creatures feed on plankton, and the freeloaders simply have to extend their tentacle-like cirri as the whale swims through the water. By way of contrast, whale lice (family: Cyamidae, related to skeleton shrimp) feed directly on the whale, eating its dead skin along with any algae they find. The crustaceans attach themselves in places that are protected from the current (often on the hump that gives this kind of whale its name) without causing the host any serious harm. In some cases a humpback whale even has barnacles on its barnacles, such as Conchoderma auritum attached to Coronula diadema, along with lots of unicellular diatoms. Thus comparing a whale’s skin to a floating reef is not an exaggeration. But how do the microscopically small larvae of these little creatures find their mobile host in the vast expanse of the oceans? “We don’t really know how they’re doing it,” admits marine biologist John Zardus. It may be a matter of sheer luck. Or perhaps a passing whale emits a chemical signal that can be detected by a barnacle’s up to 20,000 offspring: “Hop on now if you want a good meal!”