The study puts global numbers on the poor conservation status of the fauna (and, by extension, the biota) of inland aquatic environments (rivers, lakes and wetlands), a scenario already intuited from other approaches (e.g. living planet index). The work focuses on decapods (crabs and crayfish), fish and odonates (dragonflies and damselflies), to show that almost 25% of the species are threatened with extinction (i.e. fall into one of the threat categories - CR, EN or VU -, are extinct in the wild - EW - or definitely extinct - EX). This number could be higher if other groups with many threatened species, such as bivalves and other freshwater molluscs, had been included. On the other hand, it is striking that odonates are included among the aquatic organisms and amphibians among the terrestrial tetrapods. Both groups depend on water for breeding and juvenile stages, but as adults they are primarily terrestrial (in fact, odonates are, as a group, notably more terrestrial than amphibians).
The overall percentage of threatened species in aquatic environments (25%) is not evenly distributed around the world, and there are biomes and regions where the numbers are significantly higher. This is the case of the world's Mediterranean climate ecosystems (in North and South America, southern Africa, Australia and the Mediterranean basin itself), where many of the native species are threatened by the combined impacts of river regulation (with reservoirs), overexploitation of water resources, invasive species and the elimination of wetlands. The article includes a map (figure 3) showing the number of threatened aquatic species, in which the Iberian Peninsula stands out. Being a relatively poor territory in terms of the total number of species, it is striking, and very worrying, that it is home to so many threatened species.
Nor are the threats distributed homogeneously across the planet. Thus, the article mentions (citing previous work) that 37% of rivers over 1,000 kilometres in length are regulated by reservoirs (‘are no longer free-flowing’). In the Iberian context, this percentage is 100 % (and should even approach 100 % if we are talking about rivers over 100 kilometres long). Moreover, all large or medium-sized Iberian basins host at least as many invasive fish species as native ones (often many more), and are in fact among the most intensively invaded aquatic systems worldwide. Furthermore, the creation of reservoirs and the changes in flow regimes brought about by reservoir management are also conducive to the presence of invasive species. In other words, many of the threats to aquatic biodiversity act synergistically.
I think the article is important to highlight the many conservation needs of aquatic biodiversity, which often receive too little attention. Situations that occur in the management of aquatic fauna are unthinkable with birds or mammals. For example, the European eel (Anguilla anguilla) continues to be commercially exploited throughout its range, including Spain, despite being a Critically Endangered (CR) species, an inconceivable scenario for the European mink (Mustela lutreola), the Iberian desman (Galemys pyrenaicus) or the Dupont's lark (Chersophilus duponti).
In the Iberian Peninsula, protected areas have been created without taking aquatic biodiversity into account. In fact, if these areas had been created at random, by placing them anywhere, they would have protected aquatic biodiversity better than in their current configuration. State conservation strategies have systematically forgotten aquatic species, including the eel or salmon (Salmo salar), but also, and above all, species exclusive to the peninsula with a high risk of disappearing, such as the cyprinodontids (samaruc - Valencia hispanica, fartet - Apricaphanius iberus and salinete - Apricaphanius baeticus), the jarabugo (Anaecypris hispanica) or different species of the genera Squalius and Cobitis. Given this bleak outlook for native biodiversity, it is most surprising that a state strategy for the conservation of the Italian crayfish (Austropotamobius fulcisianus), a species introduced into Spain, has been drawn up.
In summary, inland aquatic systems and their biota are in a bad situation globally, and critical at the Iberian level. Their conservation requires important changes both in biodiversity management planning and in the exploitation of natural resources. And, to date, little progress has been made in this direction.