Coral - March/April 2010

The Mystery of the Disappearing Gobies Even as marine scientists have been cautiously rejoicing over the recovery of corals that had been through bleaching events on the Great Barrier Reef in the late 1990s, a new finding suggests that the almost unnoticed tiny gobies that were once found everywhere in the niches of the reef are not coming back.

From sizes of less than an inch to about 1. 75 inches (25-45mm) in length, the gobies (Family Gobiidae) are so small and cryptic they often go unseen to the casual visitor—but they make up almost half of all the fish life, as measured by number of individuals, on the reef, says ichthyologist Professor David R. Bellwood of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

“These fish may be tiny, but they are very important. They are telling us that the world has changed, and in ways we do not understand. That we may not be able to manage things as well as we hoped,” he says.

“In 1998 there was a major coral bleaching event that affected some 40 per cent of corals across a huge area of the reef. After some years, quite a lot of the coral has recovered—and looks more or less as it once did.”

30 GENERATIONS WITH NO RECOVERY “But the gobies have not come back. Something is not right if the fastest breeders of the reef are still missing.

Overall, the coral fish fauna are still in a degraded state— after 30 generations.” In a published paper several years ago, the abundance of the Green or Broadbanded Clown Goby, Gobiodon histrio, for example, had diminished 67 percent seven years after the bleaching event. (Bellwood, et al. 2006.)

Prof. Bellwood has devoted almost 20 years to the study of what many might imagine to be the least significant of fish on the reef. He feels they may be far more important than might appear, as indicators of the health status of the Reef.

“Gobies are among the Reef’s most plentiful species. They live fast and die young, in vast numbers. Many big reef fish live ten years or more: a typical goby lasts just 100 days. Everything eats them—they are the ‘Tim Tams’ (chocolate bisquit snacks) of the Reef. For every ten that wake up in the morning only nine go to sleep at night.” Studying something as small as gobies is not easy. Usually it consists of encasing a coral bommie in a large mosquito net, and then meticulously collecting anaesthetized fishes. Comparisons of goby populations over many years before and after bleaching, even in reefs with apparently healthy coral, shown signs of major change.

“Because their generations turn over so quickly, gobies provide a highly sensitive indicator of changes that may be taking place, far more so than the longer-lived species, like large fishes or turtles.