Life is tough if you live on a coral reef, particularly if you are a minute fish larvae, spawned by your parent and left to drift on ocean currents with the hope that you reach a safe coral haven. A newly discovered species of damselfish doesn't like those odds and cares for its young instead. But this adaptation could play against the species in the long run.
Aliea's damselfish, Altrichthys alelia, was found off the coast of Busuanga, an island in the Philippines. It was discovered by chance when Giacomo Bernardi and a team of graduate students were studying two other kinds of damselfish and happened upon the new fella while snorkeling away from their study site.
Photo by Giacomo Bernardi.
"Immediately, as soon as we went in the water, we saw that this was a different species," explains Bernardi. Most coral species follow the scatter-gun strategy described above, whereas A. aliea nurtures its young until they are old enough to fend for themselves. The team observed A. aliea "aggressively defending a cloud of fry" on the reef where they discovered it.
"It's very unusual to see a coral reef fish guarding its babies, so it's really cool when you see it," Bernardi continues. Out of around 360 damselfish species, only three have been observed caring for their young in a similar fashion, A. aliea makes this number four.
According to Bernardi, it seems puzzling why other species aren't following the same method. Wide dispersal methods are only around one percent effective, Bernardi says, whereas he believes A. aliea's aggressive nurturing results in survival rates of around 35 percent.
But there is also an unfortunate trade off for this success. Species that scatter their offspring in ocean currents give the youngsters the chance to colonise new reefs, far from where their parents were born. The young of brooding species like A. aliea don't have this luxury and so are left vulnerable to overcrowding of reefs or to rapid changes that may occur.
"I suspect that species evolve this strategy regularly, and they are successful until there is some change to the local habitat, and then the whole population gets wiped out," Bernardi explains. "These are very fragile species."
He points to the Banggai cardinalfish (Pterapogon kauderni) as an example. The beautiful reef fish, endemic to a small area near the Banggai Islands off Sulawesi, Indonesia, was only discovered relatively recently and now finds itself listed as Endangered by the IUCN. Overharvesting for the aquarium trade and degradation of coral reefs are the main threats to their survival.Unfortunately for the Banggai, their natural low density, limited range and strong parental instincts are playing against their hopes for survival.
So life is tough on the reef. You either spawn widely, play pot luck and hope some of your offspring grow up to colonise some distant coral home, or you invest everything in rearing them and risk it all being for nothing, at any given moment. Such is the coral reef.
P.S. On a happier note A. aliea takes its name from Alessio and Amalia, Bernardi's son and daughter who helped him with the field research.