Coral reefs in crisis – But they have vast potential

Humans are stopping proper functioning of reefs
April 2011: In an unprecedented collaborative analysis, scientists from 49 nations demonstrated that the ability of reef fish systems to produce goods and services to humanity increases rapidly with the number of species.

COMPLEX: But coral reef systems function best when there is more biodiversity

However, growing human populations hamper the ability of reefs to function normally, with the most diverse reef fish systems suffer the greatest impairments from stressors triggered by human populations.

‘Coral reefs provide a range of critical goods and services to humanity – everything from nutrient cycling to food production to coast protection to economic revenues through tourism,’ says Camilo Mora at Dalhousie University in Canada and lead researcher of the study. ‘Yet the complex nature and large-scale distribution of coral reefs is challenging scientists to understand if this natural ecosystem will continue working to deliver goods and services given the ongoing loss of biodiversity in coral reefs.

Study involved 2,000 coral reefs worldwide
‘Numerous experiments have shown that biodiversity has positive effects on several ecosystem processes, although the number of species required to ensure the functionality of a given process is fairly low, as many species often have similar ecological roles,’ says Michel Loreau from Canada’s McGill University, a co-author of the study. ‘What remained largely unknown, however, was whether the results of experimental studies reflect what happens in real ecosystems.’

To fill this unknown, 55 researchers, in a two-year study, collected the necessary data to determine whether biodiversity influences the efficiency of reef fish systems to produce biomass, and if so, work out the role of humans in such a linkage.

The team collected demographic data on human populations as well as environmental and biological data on the identity of species, their abundances and body sizes in almost 2,000 coral reef locations worldwide. The data on abundance and body size were used to calculate the cumulative weight of all fishes on each reef (also called standing biomass), which is one of the main services reef fishes provide to humanity through food supply but also a very close proxy for how effectively ecosystems produce biomass.

‘The more biodiversity the better’
‘The results of the study were stunning,’ says Kevin Gaston at Sheffield University. ‘While experimental studies have elucidated that the biomass production of ecosystems stabilises after a certain number of species is reached, this field study demonstrated that the production of biomass in reef fish systems did not saturate with the addition of new species.’

‘This study shows, quite simply, that the more biodiversity, the better,’ says Marah Hardt with OceanInk. ‘The benefits appear limitless, if we allow ecosystems to operate at their full potential.’

Michel Kulbicki of the French Institute for Research and Development said: ‘This strong relationship clearly indicates that species interact in such a way that their combined effect is larger than the addition of their individual parts and that the loss of species can have far-reaching consequences in the functioning of coral reefs.’

The study also demonstrated that standing biomass reduced with increasing human density, although for the same number of people the reduction of biomass was significantly larger in more diverse ecosystems.

‘Curbing human population growth is at the core of finding ultimate solutions for the protection of biodiversity’
‘It’s been usual to expect that diverse ecosystems could lose a few species without it mattering very much because the high redundancy of species should allow the replacement of any species that is lost,’ said Peter F. Sale, assistant director of the Institute for Water, Environment and Health of the United Nations University, who was not involved in the study.

‘The results of this study now suggest that we do not have such insurance and that reef ecosystems are at greater risk from human pressures than we previously thought.’

The negative impact of humanity on reef fish systems can be widespread, as some 75 per cent of the world’s coral reefs are near human settlements and could worsen, as 82 per cent of countries with coral reefs are expected to double their human populations within the next 50 to 100 years.

‘Unfortunately, we find again and again that our global population cannot be sustainably supported without the deterioration of the world’s natural resources and the resulting backlash on human welfare,’ says Mora. ‘Thus, identifying socially and politically acceptable solutions to curb human population growth is at the core of finding ultimate solutions for the protection of biodiversity and the prevention of unnecessary hardship.’

‘This is a critical situation,’ says coauthor Sebastian Ferse from the Leibniz Center of Tropical Marine Ecology. ‘It underlines once again that current management approaches are insufficient to protect marine biodiversity on a large scale, and that holistic approaches combining natural and social systems are needed.’

However it was not all doom and gloom. The study reported that at least 25 per cent of the world’s reefs remain distant from direct human effects. Those reefs are located on small and isolated areas where human habitation is sparse. ‘These few reefs are in stark contrast with degraded sites, and may still be able to act as sources to replenish others. This is a fortunate situation that can buy us some time while we figure out effective solutions to this coral reef crisis.’

artificial fish habitat at fishiding.com