Friday, January 27, 2012

Reef News

Many things around HSC are continually changing; such is life in our 210 gallon reef tank. The tank’s charm lies not so much in its capacity to hold liquid but its capacity to support marine biota. Here in Bemidji we are about as far from the ocean as anyone on Earth could be, so this tank has been a bit of a local spectacle. We are lucky to have had it donated to us. Come see it if you haven’t lately.

The task of reef tank maintenance is formidable, as it takes a generous input of energy, a plethora of specialized equipment, pure H2O, NaCl (sodium chloride = salt), the right combination of living elements, and timely applied human capital. It is all worth it, though, when you hear the excitement it generates, especially with young children. The little ones shriek and shrill as they easily recognize Nemo and Marlin (Clownfish––Amphiprion percula). Pixar and its computer animators helped make these lovable vertebrates a popular part of the America’s entertainment lexicon, and in so doing they actually reinvigorated the reef aquarium industry.

Let’s tell part of a tale that two very different species share. Clownfish live in a "symbiotic" (mutually beneficial) relationship with our bubble tip anemone (Entacmaea quadricolor). Clownfish are very busy fish and extremely aggressive. Because they are quite active, the clownfish are thought to be "clowning around." Clownfish perform an elaborate dance with an anemone before taking up residence, gently touching the bubble tipped tentacles with different parts of their bodies until they are acclimated to their host. A layer of mucus on the clownfish skin makes it immune to the fish-eating anemone’s lethal sting. In exchange for food scraps and safety from predators, the clownfish drives off intruders and preens its host anemone, removing parasites.

Clownfish spend their entire lives with their host anemone, rarely straying more than a few meters from it. They lay their eggs about twice a month on the nearest hard surface concealed by the fleshy base of the anemone, and they aggressively protect the developing embryos. Just after a clownfish hatches, it drifts near the surface for a week or two as a tiny, transparent larva. Then it metamorphoses into a miniature clownfish about a centimeter long that descends to the reef. If the young fish doesn’t find an anemone and acclimatize to its new life within a day or two, it will die.

Surprisingly, all clownfish are born male. They have the ability to change their gender, but will do so only to become the dominant female of a group. This change is irreversible! Should the female in the anemone group die, the dominant male then becomes female and breeds with one of the males that inhabit the same sea anemone. Changing gender is not particularly rare among coral reef fish, but most change from female to male.

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