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Focus on freshwater conservation, and land gets swept along for the ride

Prioritizing terrestrial species leaves freshwater ones behind — but the opposite isn't true.
November 11, 2020

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Rivers, wetlands, ponds and streams punch above their weight. Freshwater ecosystems are home to hundreds of thousands of species, from tiny duckweeds and jewel-perfect diatoms to lake-covering water lilies and leaping river dolphins. They provide humans with speedy transport, food and materials, recreation, and of course fresh water. And they do it all while taking up just 1% of the planet’s surface, and one hundredth of one percent of its H2O.

But when it comes to conservation, we often forget all about fresh water. Most plans for protected areas prioritize dry land and its creatures, assuming that the benefits will trickle down to any watery spots that happen to be nearby. 

That’s not necessarily true. In fact, according to recent research in Science, it’s the other way around. If you plan your protected area to maximally benefit terrestrial species, freshwater species don’t fare very well. But work explicitly on freshwater conservation, and nearby landlubbers do just fine —suggesting that we might be well-served by redirecting our focus.

Cecília Gontijo Leal, the paper’s lead author and a postdoctoral researcher at the University of São Paulo, has always been interested in freshwater ecosystems. After 10 years studying the Amazon, she is particularly concerned with the small streams that web the rainforest—bringing water to local communities, linking people and animals with larger rivers, and providing homes for endemic, rare and yet-to-be-discovered species. “They receive much less attention, but they are super important,” she says. 

For this study, Dr. Leal and her team concentrated on two areas in the Brazilian Amazon. They put data about each area’s terrestrial and freshwater biodiversity into a conservation planning software program. They then asked the software to pick 20% of each area to conserve—focusing first on maximizing benefits to terrestrial species, and then repeating the exercise to prioritize freshwater species. 

Prioritizing terrestrial species provided “limited incidental conservation benefits for freshwater species,” the authors write—around 22% of what could be achieved by planning solely around those species. In other words, “if you focus only on the terrestrial, it’s representing very little of the freshwater,” Dr. Leal says. 

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If you focus on freshwater instead, though, terrestrial benefits tag along. Maximizing benefits to aquatic species resulted in about 84% as good an outcome for terrestrial species as would occur in a terrestrial-focused scenario, the authors write. 

And meeting in the middle—balancing the needs of both water and land species— resulted in huge gains for freshwater species with a very minimal terrestrial sacrifice, they write: “Freshwater benefits could be increased by on average 62 and 345% in Paragominas and Santarém, respectively, for a negligible 1% reduction in terrestrial benefits relative to their optimum.”

What is responsible for these patterns? Effective freshwater planning regimes prioritize places like catchments that set the tone for the whole ecosystem. Terrestrial-first ones may incidentally include rivers and streams, but only in pieces, without maintaining the linkages that keep them thriving. “The main thing is the connectivity,” says Dr. Leal.

While this research focused on the Amazon, many parts of the world are currently reckoning with freshwater species declines—a 2018 report found that the world’s river, lake, swamp and pond populations have dropped by at least 83% in the past fifty years. Meanwhile, at least 500 dams—enemies of that vital connectivity—are currently being built or planned within the world’s protected areas. Keeping freshwater species at the forefront of the conservation conversation could help to reverse these trends. After all, why not invest in this extraordinary biome that does so much with so little?

Source: Leal, Cecília G., et al. “Integrated terrestrial-freshwater planning doubles conservation of tropical aquatic species.” Science, 2020.


Image: Marizilda Cruppe

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