Such an overall decline has never been documented before. "Our study indicates that Caribbean-reef fish populations may be more vulnerable than previously expected," lead author Michelle Paddack of Simon Fraser University, Canada, told environmentalresearchweb. "As well as known threats from fishing, these populations may now be responding to habitat loss as a result of widespread coral die-off."
The researchers obtained their results using a technique called meta-analysis, which has long been used in the medical and social sciences. Since no single research group or organisation has been able to survey such a large area as the Caribbean, this type of technique allows scientists to unify individual efforts from many groups and covers a period of time as long as 50 years, explained Paddack.
The analysis included 273 reef fish species. Being able to study so many species for general trends is another strength of the meta-analytic method, she added. "This does not mean that every single species is in decline, or that the rate of decline is equal, but the general trend is definitely negative."
Although the analysis did not specifically address the cause of the decline, the findings suggest that it is probably related to degradation of coral reefs over the last 30 years. Indeed, previous research has shown that live coral in the Caribbean has declined by 80% since 1977. This loss may not have had an immediate impact on fish because it takes time for coral skeletons to break apart, even after the coral itself has died. However, if no new coral replaces the dead, fish no longer have anywhere to hide from predators.
The decline may also be a result of accumulating stressors, said Paddack. "Some types of fishing, for example, may not seriously deplete stock but when combined with deteriorating habitats the impact on fish populations may suddenly be too great."
The results confirm earlier, smaller-scale studies in the Indo-Pacific, which also showed that reef fish are disappearing. This earlier research dealt with fish populations that were more directly dependent on coral. "Our study indicates that even when coral dependency is not direct, negative consequences may result from loss of live coral," she said.
The result is important for policy makers and resource managers because it highlights a decline that was not immediately apparent. It might even be used to possibly halt the decline and promote recovery. "There are many ways that this could be done, depending on the situation of individual countries, but some solutions include reduced fishing, implementing better fishing techniques that are not not destructive to reefs, and establishing protected marine areas to alleviate stress from fishing," suggested Paddack. Other solutions include mitigating global warming by reducing carbon-dioxide emissions, keeping boat traffic farther offshore and in designated shipping channels, and re-establishing coral where it has died.
"What will turn things around is our awareness of these grave losses on reefs and our desire to save these beautiful and important ecosystems," said Paddack.
This will be no easy task because Caribbean reefs are governed by more than 20 nations, and putting together a unified management plan will be a huge challenge. But until then individual countries and territories can make a big difference, stressed Paddack. "For example, Bonaire has set up a diver-awareness programme and has restricted anchoring on coral reefs to ensure that anyone who visits these waters is causing the least damage possible. The result is an informed public that is engaged in reef protection."
The team, which includes scientists from the UK, US, Cuba, Hawaii, Jamaica, the Netherlands and Colombia, is now studying groups of fish species that are important to reef ecology - for example, herbivores and cleaner fish. "We are also collaborating with other researchers who have investigated coral reef community dynamics and reef structure, and are examining how tightly linked these processes are," said Paddack.
The scientists reported their work in Current Biology.