Conserve freshwater or land biodiversity? Why not both, new study asks

Integrating aquatic biodiversity into conservation planning could yield substantial benefits for freshwater species with minimal cost to terrestrial creatures, according to a study published in Science last month.

Conservation areas are often determined based on the needs and distributions of terrestrial species, under the assumption that preserving an area important for the target species will also have benefits for the other species living there, a phenomenon known as “incidental conservation.”

To test this assumption, an international and interdisciplinary team of researchers led by Cecília Gontijo Leal at the University of São Paulo (USP) and the Federal University of Lavras (UFLA) in Brazil examined the costs and benefits to different groups of organisms from prioritizing terrestrial or freshwater biodiversity in conservation planning. They surveyed plants, birds, fish and insects in the municipalities of Paragominas and Santarém in the Amazonian state of Pará, Brazil, to create species distribution maps, and then applied a framework known as zonation conservation planning, which recommends areas for conservation that offer the widest benefits for biodiversity and ecosystem services.

Their analysis showed that focusing conservation planning on the needs and distributions of terrestrial species alone tended to do little for freshwater species — offering just 22% of the benefits that could be achieved with freshwater-focused planning. Planning based only on the needs of aquatic species, on the other hand, also benefited plants and animals on land — securing 84% of the benefits achieved with a terrestrial focus. But the biggest benefits can be achieved with an integrated approach, the authors say.

Integrated planning, considering both terrestrial and freshwater species, increased the benefits to freshwater species by an average of 62% in Paragominas and 345% in Santarém, while only reducing the benefit to terrestrial species by 1% compared to terrestrial-focused planning.

Leal says she was surprised by the magnitude of these results. “We had this expectation that maybe there would be much more conflict” between the needs of terrestrial and freshwater species, she said.

“The rather remarkable result is that the trade-off on the protection of terrestrial biodiversity is very minimal in the two regions that they examined and the converse is not true, a focus on terrestrial conservation doesn’t necessarily provide major benefits to the freshwater realm,” said Kirk Winemiller, an aquatic ecologist at Texas A&M University, who was not involved in the study. “It’s a very important paper because it promotes freshwater biodiversity conservation in the Amazon, which is something we know we need badly,” he added.

Freshwater ecosystems, such as rivers, lakes and streams, cover just 1% of the Earth’s surface but are home to 10% of all described species. The Amazon is a hotbed of freshwater diversity: it is estimated that nearly one out of every 10 fish species on Earth lives in the streams and tributaries of the Amazon Basin. But aquatic species are often neglected in conservation planning, in part because far less is known about them than their neighbors on land, and freshwater populations have declined by more than 80% since 1970 compared to 40% for land and marine organisms.

“I think it’s a really good study with an incredible dataset,” said Cristina Banks-Leite, a tropical ecologist at Imperial College London, who was not involved in the study. “It’s one of those messages that are important to be said and came at the right time.”

The team performed their analysis by dividing the land into units according to river catchments or watersheds — areas of land where water drains into the same river or lake. This approach also allowed them to take into account river connectivity, which is crucial for freshwater species to disperse and breed.

“Thinking about a catchment and hydrographic basins makes sense because the cycle of water and the terrestrial system are completely connected,” Leal said. “When we think of isolated pixels or squares for terrestrial ecosystems it is completely disconnected from the way that freshwater works.”

Furthermore, by focusing on river catchments, “you’re connecting much larger areas,” said Banks-Leite. “I think that’s why you end up having such high co-benefits to terrestrial biodiversity.”

Experts agree that freshwater connectivity is likely to be important in almost all biomes, making these results broadly applicable to other habitats, but they note the magnitude of the benefits from an integrated focus might be smaller in ecosystems with more heterogeneous conditions, such as temperate mountainous regions. “There ought to be more studies of this nature conducted in other regions of the world where we’re facing serious threats,” Winemiller said.

While it might seem obvious that integrated planning would yield benefits for biodiversity, “what we bring is evidence of the obvious and it’s important because without evidence it’s difficult to justify and to build more knowledge,” Leal said.

Integrated approaches may have been hampered by the separation of terrestrial and aquatic ecology into distinct disciplines in academic research. “There are a lot of passionate people doing great science in both of those realms but they don’t often collaborate together, that’s what’s kind of fresh about this paper,” Winemiller said.

Another reason studies like this have rarely been attempted is that comprehensive sampling of biodiversity, especially in tropical regions, can be extremely challenging. “It is really hard to sample freshwater biodiversity, I mean big kudos to the authors because studying fish and invertebrates in the Amazon is immensely hard,” Banks-Leite said.

The study comes just as policymakers and stakeholders prepare to negotiate new goals, targets and conservation frameworks for the coming decades, including under the Convention on Biological Diversity’s post-2020 Global Biodiversity Framework, which is due to be published next year. Leal said including integrated planning for terrestrial and freshwater species in new international targets like this would be “the cherry on top” for her with this piece of research.

Banks-Leite agreed: “I hope this is a kind of wake-up call for other scientists and politicians.”

The study could also have implications for national and regional policymaking. For example, in Brazil’’s nine Amazonian states, private landowners are mandated to preserve 80% of their property as legal reserves, but the location of these reserves is not prescribed, so they are commonly assigned to the land least suited to agriculture. Leal says that taking freshwater connectivity into account when planning legal reserves could offer benefits to farmers and biodiversity. “Maybe small changes [in zoning] would make a big difference for conservation,” she said.

Citation:

Leal, C. G., Lennox, G. D., Ferraz, S. F. B., Ferreira, J., Gardner, T. A., Thomson, J. R., … Barlow, J. (2020). Integrated terrestrial-freshwater planning doubles conservation of tropical aquatic species. Science, 370(6512), 117-121. doi:10.1126/science.aba7580

Banner image: A still from A River Below. Conservation of freshwater ecosystems is key for the future of the Amazon Rainforest and the 34 million people who call it home. Image courtesy of Sandarba Productions.