Reef diversity no insurance against human threats

In a large collaborative analysis publishing tomorrow in the online, open access journal PLoS Biology, 55 scientists from 49 nations document that the capability of reef fish systems to produce biomass and deliver goods and services to humanity, is functionally linked to the number of species; functioning increases as biodiversity increases. However, mounting pressures from growing human populations is tampering with this functioning of the reef fish communities, especially in the most diverse reefs. The extent of this distress was shown to be widespread and likely to worsen as some 75% of the world's coral reefs are near human settlements and because most countries with coral reefs are expected to double their human populations within the next 50 to 100 years. A two year study was initiated to collect the necessary data to determine if biodiversity influences the functioning of reef fish systems, and if so, elucidate the role of humans in such a linkage. The team collected data on the identity of species, their abundances and body sizes in almost two thousand coral reef locations worldwide. These data were then used to calculate the standing biomass of reefs, which is one of the main services reef fishes provide to humanity through food supply but can also be used as a proxy for biomass production, which is among a metric of ecosystem functioning used in previous studies. The data on diversity and standing biomass were combined with demographic data on human populations and analyzed with sophisticated statistical approaches to determine the linkages between biodiversity, functioning and people.

The study demonstrated that biomass, and therefore ecosystem functioning, decreased with increasing human density although for the same number of people the loss of function was significantly larger in more diverse ecosystems. The stronger deleterious effect of humanity on more diverse reefs is possibly due to the selective local extinction of large fishes, which may have a disproportionate affect on function and whose ecological roles are less likely to be replaced by other species.. Unfortunately, the study documents that the deleterious effect of humanity is widespread and likely to worsen in the near future, as some 75% of world's coral reefs are near human settlements and because almost all countries with coral reefs are expected to double their populations within the next 50 to 100 years.

"Coral reefs are the most diverse ecosystem on the planet hosting thousands of species and generating goods and services through food, tourism and coastal protection to millions of people worldwide" says Enric Sala, a National Geographic fellow and coauthor of the study. "The future of coral reefs and the services they provide to a growing human population depend on how soon countries become seriously committed to regulating human threats" he adds.

Nevertheless, the study also reports that at least 25% of the world reefs remain distant from direct human effects. Those reefs are located on small and isolated areas where the habitat is too harsh for humans to live. Such isolated reefs might provide a potential source to replenish degraded reefs when solutions to the coral reef crisis can be determined.

"Human overpopulation is a very sensitive topic across endeavors from science to religion and politics" says Camilo Mora at Dalhousie University and lead researcher of the study.. "Unfortunately, we find again and again that our global population cannot be sustainably supported without the deterioration of the world's natural resources and its' backlash on human welfare. 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."

Source: Public Library of Science