Biodiversity protects fish

Biodiversity is more than a pretty face. Preserving biodiversity is not just an aesthetic or spiritual issue - it's critical to the healthy functioning of ecosystems and the important services they provide to humans, like seafood.

The accelerating loss and shifts of species across the globe have troubled scientists and the public for a while already. But, believe it or not, the question of whether biodiversity offers practical value - for humans and ecosystems - remained controversial. A new study, just published in the PNAS, offers the most comprehensive proof yet that preserving e.g. marine biodiversity can benefit people as much as it benefits the oceans.

Reef Life Survey is a comprehensive program that has conducted more than 4,000 underwater surveys of more than 3,000 fish species in 44 countries around the world. Many of the surveyors were volunteer citizen scientists, about a third of whom with no scientific background. Volunteer divers actually received training from some of the program's lead scientists at the University of Tasmania in order to enable them to collect data using standardized methods.

With this comprehensive global dataset on marine biodiversity involving standardized counts, the researchers tracked how 11 different environmental factors influenced total fish biomass on coral and rocky reefs around the world. Surprisingly, one of the strongest influences was biodiversity: Species richness and functional diversity enhanced fish biomass. The boost in fish resources provided by biodiversity was second only to that of warm temperatures.

Temperature showed a more complex relationship with fish biomass: Warmer ocean temperatures tended to boost fish biomass on average, while wider temperature fluctuations hindered it. But biodiversity made fish communities more resilient against changing climate. In communities with only a few species, fish biomass tended to increase with rising temperatures until seas warmed above 20°C, at which point biomass decreased. Communities with many species remained stable at these higher temperatures.

The researchers found a similar buffering effect of diversity against temperature swings. While both high- and low-diversity communities were less productive under fluctuating temperatures, high-diversity communities suffered only half as much as low-diversity ones. The researchers suspect communities with more species are better equipped to handle temperature changes because they have more of their bases covered. When temperatures fluctuate, a community with numerous species has better odds that at least a few species can thrive in the new normal.

This work is a critical step forward in linking insights from experiments in buckets and garden plots to the larger world. It shows that experimental ecologists have in fact been on the right track for 20 years, and that biodiversity is paramount to how natural systems work. The results demonstrate that preserving local biodiversity is not only an ethical directive with aesthetical and genetic insurance value, but that it is an imperative for human life,