Biodiversity Helps Protect Fish From Climate Change

By on May 20, 2016
Goliath groupers. (Credit: Graham Edgar / Smithsonian)

Scientists from the Smithsonian’s Tennenbaum Marine Observatories Network and other international institutions have found that biodiversity helps to make marine fish communities more productive and resilient to temperature swings. In the face of predicted climate changes, the find underscores the importance of promoting biodiversity, both for fish but also because humans rely on them as seafood.

Fish species losses are pretty much troubling to researchers all around the world. But there has been some difficulty in forming consensus about the true value that biodiversity provides. The new study, posted online in the Proceedings of the National Academy of Sciences, offers some of the strongest proof yet that preserving biodiversity can benefit people as much as it does fish.

The discovery came out of the Reef Life Survey, a comprehensive program that has conducted 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 had no scientific background. Volunteer divers from 11 countries received training from the program’s lead scientists at the University of Tasmania to collect data using standardized methods.

The study was based on more than 4,000 underwater surveys, allowing scientists to achieve comprehensive coverage of the world’s reefs, from tropical to polar waters. Armed with the most 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.

Reef Life Survey diver observing leafy seadragon in southern Australia. (Credit: Graham Edgar / Smithsonian)

Reef Life Survey diver observing leafy seadragon in southern Australia. (Credit: Graham Edgar / Smithsonian)

Surprisingly, one of the strongest influences was biodiversity: The number of species (species richness) and the variety in how they use their environment (functional diversity) enhanced fish biomass. The boost in fish resources provided by biodiversity was second only to that of warm temperatures.

Temperatures had 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 a changing climate.

In communities with only a few species, fish biomass tended to increase with rising temperatures until seas warmed above 20 degrees Celsius (68 degrees Fahrenheit) — at which point biomass started to fall. But communities with many species remained stable at the higher temperatures.

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.

Scientists 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.

Researchers say that the findings show that ecologists have been on the right track for decades in pushing the merits of biodiversity.

Top image: Goliath groupers. (Credit: Graham Edgar / Smithsonian)

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