Post by conrad on Feb 17, 2010 9:17:52 GMT -5
Mystery of the Disappearing Gobies
Unidentified Eviota goby on the Great Barrier Reef. Photo by j.P. Krajewski | ARC Centre of Excellence for Coral Reef Studies.
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.”
Prof. Bellwood, right, 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 from within the net. Comparisons of goby populations over many years before and after coral bleaching, even in reefs where the coral is apparently healthy, shown signs of significant 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.
“Normally gobies breed up quickly and replace their numbers. But in many areas which have suffered from the effects of coral bleaching and other impacts caused by human activity, many are largely missing today—a signal that something is seriously wrong.
Uncertain Future for Bleached Reefs
“Gobies divide up the ecological niches on the Reef very finely - they tell us if the Reef system, as whole, is thriving or failing. Now, they are telling us that the foundations of the Great Barrier Reef and other coral reefs around the world are shifting in unexplained ways.
“This may be a sign that coral reefs will never be the same again, and that we should be planning for an unstable, uncertain future.”
Bellwood says that “Few if any disappeared, but many are exceedingly rare in our sampling area. We have not lost species but have tracked a major change in composition. The equivalent of your house pets (cats, dogs, fish) being replaced by rats mice and cockroaches - you still have animals in the house just not the same sort.”
The successful invaders include Chinese Damsel (Neopomacentrus bankieri), crypto-benthic gobies in the Genus Istigobius, and the Queensland Pygmy Goby (Eviota queenslandica). Bellwood says it is not yet possible to diagnose the precise reasons for the loss of the gobies, but suspects that reproductive success has diminished because of unknown and difficult to measure chemical changes in the reef itself.
Absence of Genetic Settlement Cues for Larvae?
“I suspect a comparable, but unrecorded, change in the benthic composition has changed the settlement cues and made the reef less attractive to the larvae of the original inhabitants. The larvae of the species in the original community are still not coming back in their original numbers.” (Editor: A settlement cue is a signal to a drifting larval fish that this is "home" and a good place to drop down out of the water column. Settlement cues for larval marine organisms are given off by coral tissue, coralline algae, and other, undocumented sources.)
“What is shocking is that these fishes have such short lifespan that many generations are passing with no recovery. These things live for only 100 days with Eviota sigillata (Seven-figure Pigmy Goby) having the world record - it only lives for 59 days—max.”
Bellwood says that his team will be doing annual checks on the status of the gobies and their rank in the recovering reefs. “I’m one of a handful of scientists in the world working on goby ecology, and we still know little more about them than we did when Charles Darwin visited Australia. But because of their vast numbers, rapid growth rates and fast turnover, they are a real powerhouse for the reef, providing nutrition for a great many other species directly or indirectly. If they disappear from the system, it signals something is profoundly amiss.”
--------------------------------------------------------------------------------
References
From materials released by the ARC Centre of Excellence, James Cook University, Townsville, Australia.
ARC Centre of Excellence for Coral Reef Studies — www.coralcoe.org.au/
Bellwood Lab — www.coralcoe.org.au/research/bellwoodlab/home%20page.htm
Unidentified Eviota goby on the Great Barrier Reef. Photo by j.P. Krajewski | ARC Centre of Excellence for Coral Reef Studies.
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.”
Prof. Bellwood, right, 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 from within the net. Comparisons of goby populations over many years before and after coral bleaching, even in reefs where the coral is apparently healthy, shown signs of significant 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.
“Normally gobies breed up quickly and replace their numbers. But in many areas which have suffered from the effects of coral bleaching and other impacts caused by human activity, many are largely missing today—a signal that something is seriously wrong.
Uncertain Future for Bleached Reefs
“Gobies divide up the ecological niches on the Reef very finely - they tell us if the Reef system, as whole, is thriving or failing. Now, they are telling us that the foundations of the Great Barrier Reef and other coral reefs around the world are shifting in unexplained ways.
“This may be a sign that coral reefs will never be the same again, and that we should be planning for an unstable, uncertain future.”
Bellwood says that “Few if any disappeared, but many are exceedingly rare in our sampling area. We have not lost species but have tracked a major change in composition. The equivalent of your house pets (cats, dogs, fish) being replaced by rats mice and cockroaches - you still have animals in the house just not the same sort.”
The successful invaders include Chinese Damsel (Neopomacentrus bankieri), crypto-benthic gobies in the Genus Istigobius, and the Queensland Pygmy Goby (Eviota queenslandica). Bellwood says it is not yet possible to diagnose the precise reasons for the loss of the gobies, but suspects that reproductive success has diminished because of unknown and difficult to measure chemical changes in the reef itself.
Absence of Genetic Settlement Cues for Larvae?
“I suspect a comparable, but unrecorded, change in the benthic composition has changed the settlement cues and made the reef less attractive to the larvae of the original inhabitants. The larvae of the species in the original community are still not coming back in their original numbers.” (Editor: A settlement cue is a signal to a drifting larval fish that this is "home" and a good place to drop down out of the water column. Settlement cues for larval marine organisms are given off by coral tissue, coralline algae, and other, undocumented sources.)
“What is shocking is that these fishes have such short lifespan that many generations are passing with no recovery. These things live for only 100 days with Eviota sigillata (Seven-figure Pigmy Goby) having the world record - it only lives for 59 days—max.”
Bellwood says that his team will be doing annual checks on the status of the gobies and their rank in the recovering reefs. “I’m one of a handful of scientists in the world working on goby ecology, and we still know little more about them than we did when Charles Darwin visited Australia. But because of their vast numbers, rapid growth rates and fast turnover, they are a real powerhouse for the reef, providing nutrition for a great many other species directly or indirectly. If they disappear from the system, it signals something is profoundly amiss.”
--------------------------------------------------------------------------------
References
From materials released by the ARC Centre of Excellence, James Cook University, Townsville, Australia.
ARC Centre of Excellence for Coral Reef Studies — www.coralcoe.org.au/
Bellwood Lab — www.coralcoe.org.au/research/bellwoodlab/home%20page.htm
