Whether it’s the stock market or a vibrant coral reef, it usually pays to hedge your bets. Similar to how diversifying your stock holdings minimizes the risk of a catastrophic financial loss, biodiversity minimizes the risk of damage to ecosystems in the wake of disturbances. With lots of species present, if one suffers or is lost altogether, another can more easily take its place. Scientists call this the portfolio effect.
Recently, a new study from the Tennenbaum Marine Observatories Network examined the role of diversity in detail, using Reef Life Survey’s global database of 4,556 standardized fish surveys. They were particularly interested in the factors that influence fish biomass at any given location—an important protein resource for people in many areas. The study found that temperature is the most important factor, with warmer places, like coral reefs, having higher fish biomass on average.
Why is temperature so important? Because temperature strongly affects metabolic rates, the direct effect of temperature was perhaps not surprising. But digging deeper, it turned out that a big part of the explanation was that warmer places have more fish species, and this higher diversity itself also allows more fish to share a location.
This potato cod (Epinephelus tudula) swims through a no-fishing zone in the northern regions of the Great Barrier Reef. © Graham J. Edgar
Nearness to human populations was the third most important influence—lots of people nearby meant lower fish biomass—as expected, since reef fishes are prime targets for fishers. But the big surprise was that biodiversity was often as, or more, important than the effects of people. That is, fish biomass was greater where there were more species, even when other factors were similar between sites. For this reason, they argue, preserving biodiversity is an important part of our toolbox in the fight to preserve our ocean ecosystems and their ability to keep providing services like seafood production.
Where things got really interesting was how all these different influences interacted. The most diverse reefs—those with the most fish species—were also the least sensitive to the detrimental effects of very high and variable temperatures on biomass. This means that more diversity can provide some protection against the threat of climate change.
Fish biomass is hugely important to people, with over two billion of us relying on fish for food globally, so healthy marine ecosystems are more important than ever. The lesson from this study is that as in the stock market, diversity can be very beneficial in a risky world.