Reef Life Survey and species diversity

As a participant in citizen science, you can learn new things, explore new places and ideas, and have fun. It can even make a valued contribution to science — which is exactly what trained recreational scuba divers who participated in the global project Reef Life Survey did for a new paper published recently in Nature.

These citizen scientists have been a busy bunch, undertaking some 4,357 transects at 1,844 sites. These divers weren’t just found in those nice warm tropical waters either, spreading out to 74 of the world’s marine ecoregions and finding some 2,473 species of fish.

These very wide-ranging data — all collected in the same manner — have thrown up something interesting. Sure, coral reefs have really high fish-species richness. Using a raw count of the number of different species, they are, as far as we know, the most species-rich of all marine habitats. But does that mean that coral reefs are the most diverse system? Perhaps not.

Rick Stuart-Smith, of the University of Tasmania's Institute for Marine and Antarctic Studies in Australia, together with a team of international scientists, has taken a new tack in measuring diversity.

As well as species richness and evenness — the distribution of individuals in a species — they have also calculated functional diversity, which is based on a species’ functional position in the ecosystem in which it is found.

These traits include trophic group, what periods of the day or night a species is most active, and its preferred substrate. As one of the authors, Jon Lefcheck of the Virginia Institute of Marine Science in the USA, said:

“By gathering information on the animal's traits — what they eat, how they move, where they live — we can understand more about how dissimilar they are. Dissimilarity is the essence of diversity.”

This functional diversity showed some very different global patterns from species richness. Instead of highlighting those nice warm tropical areas, the work pointed to nutrient-rich temperate regions as being the most diverse.

Perhaps more importantly, functional diversity was not necessarily correlated with species richness or evenness. For example, temperate-region hotspots tended to have higher functional diversity and evenness relative to richness than the tropics.

Here’s the ‘so what’ factor. When we are looking at protecting the marine environment, we tend to use richness as a way of selecting areas in most need of protection. These areas may have many species that can perform the same role, so if you lose one species of fish, another may step in its place and the ecosystem will continue to function.

But if you have only a few species — or even just one — that can perform a particular functional role, and that species is lost, then the impact on the ecosystem can be much more significant.

The researchers argue that, to help ensure the long-term persistence of vulnerable marine ecosystems, managers need to take functional diversity into account when prioritising areas for protection.

This article was written for the Marine Scientist magazine.