24% of freshwater species face a serious threat of extinction

For far too long, the loss of biodiversity in our rivers and lakes has remained out of sight and out of mind. As a freshwater ecologist, I have often been frustrated by the dominance of land and marine species in conservation and research, despite rivers, lakes, ponds and other wetlands supporting a hugely disproportionate share of the world's biodiversity within their relatively small area.

That may now change with the publication in Nature of the first comprehensive assessment of extinction risk among freshwater species. The researchers drew on the recently completed "red list" for freshwater fish, as well as the list for dragonflies and damselflies.

Red lists are official records of conservation status compiled by the International Union for Conservation of Nature (IUCN). The scientists combined these with information from the previously published red list for freshwater crabs, crayfish and shrimps, assessing more than 23,000 species in total.

The authors conclude that almost a quarter (24%) of freshwater species are threatened with extinction. In other words, they have been formally assessed as vulnerable, endangered, critically endangered or extinct in the wild.

Among them are the critically endangered European eel and the endangered white-clawed crayfish, both once abundant in the streams of my childhood.

Gaps in freshwater species data

The estimates carry some uncertainty, particularly because there is not enough information to determine the extinction risk for certain species. The authors use an accepted, robust method to account for this uncertainty, but note that a substantially larger proportion of freshwater species lack data than species living on land.

Indeed, although there are indications that a greater proportion of freshwater molluscs face extinction, the authors could not include them in their analysis because data are deficient for so many species.

Our understanding of the status of the wide range of other freshwater species is also only rudimentary. This is especially true of invertebrates such as mayflies, stoneflies and various beetles, many of which are highly sensitive to pollution. The new study is an important advance in our understanding, but it should also serve as a clarion call to galvanise efforts to close these critical data gaps.

Freshwater species overlooked

The finding that 24% of freshwater species are threatened with extinction is shocking, but it is comparable to the estimate for predominantly land-based amphibians, reptiles, birds and mammals, 23% of which are threatened.

Comprehensive assessments of birds, amphibians and mammals have been available for more than 20 years, and repeat assessments are now available too.

Because the IUCN's red lists document biodiversity trends and inform national and global strategy, data on terrestrial vertebrates have dominated conservation science and policy. As a result, global environmental governance has so far concentrated on land and marine ecosystems, despite evidence that freshwaters have distinct management needs.

The new assessment makes clear that policy must be developed to protect freshwater species and improve their prospects. This requires considering entire river basins rather than just the immediate areas occupied by individual species.

It also involves taking account of how rivers and lakes are connected and how water availability changes between seasons.

Freshwater bodies resemble islands in a sea of land. Helping species move between these islands can support their preservation, particularly where they disappear seasonally.

Most freshwater species face multiple threats

Pollution, dams, water abstraction, land-use change, over-exploitation, invasive species and disease all feature prominently as threats in the new study, with most species affected by more than one. Freshwaters in areas of limestone and other porous, calcium-rich rocks consistently support more threatened species than expected. This underlines the importance of chalk streams, for example, where pressure from water resource exploitation and pollution is pronounced.

Current efforts to hold UK water companies responsible for reducing sewage inputs into rivers and lakes are commendable. However, water-use efficiency and run-off should be considered throughout decision-making, from building design and town planning to our individual daily water use.

Nature-based solutions, including tree planting and wetland protection, offer a way forward that benefits both biodiversity and human well-being.

Why freshwater biodiversity matters

A lack of understanding can no longer justify inaction. As the study's authors point out, freshwaters support more than 10% of all known species, including about a third of vertebrates and half of fish, despite covering less than one percent of the Earth's surface.

Many freshwater species assessed in the study have social and economic importance. Freshwater fish are an important source of protein for many human societies, while species such as Atlantic salmon support a fishing-tourism industry that is critical to many areas with limited opportunities to generate income.

Other species may appear unimportant to human society but thrive in clean water. Their widespread decline reflects increasing pollution and other pressures, which does not bode well for our society as it faces climate change and diminishing water availability.

Iwan Jones, Freshwater Ecologist and Head of the River Communities Group, Queen Mary University of London

This article is republished from The Conversation under a Creative Commons licence. Read the original article.