Today is March 14, International Rivers Day, and to commemorate it we will expose one of the greatest risks that these ecosystems suffer, especially in recent decades. According to the latest reports, there are a total of 200 already established exotic species in the Spanish riverbeds, of which 156 are animal species. Of all of them, the Catalog of Exotic Species includes a quarter, therefore, a significant number of invasive species are not yet cataloged as such, either because they are not yet widespread enough, because they do not yet cause enough impacts, or because they have not yet been proposed for inclusion.
From this long list we will distill those that, based on their impact on the environment, we could consider the five most dangerous invaders of Spanish rivers.
the apple snail
Pomacea canaliculata is a species of freshwater snail native to South America. It is a predator of aquatic plants that was introduced as an aquarium animal and as a food source. It represents a threat to many wetlands around the world.
Given its voracity, the apple snail’s greatest impact is the destruction of aquatic vegetation , leading to drastic habitat modification; the huge number of dead plants cause the eutrophication of the water. This favors the proliferation of microorganisms that cloud the water, prevent light from passing through and inhibit the development of new aquatic plants . Increased decomposition coupled with the absence of plants causes the loss of oxygen from the water, and animals are forced to choose between moving or dying.
In some regions it can be particularly dangerous in economic terms, mainly in rice crops. In fact, this species is not found in the Catalog of Invasive Alien Species because it is already considered in the list of harmful organisms of the plant health regulations.
Carp
Introduced for the first time —that is known— at the end of the 16th century, the carp ( Cyprinus carpio ) was not considered a danger, since the introduced population was so small that, although it naturalized without problems, it did not invade. However, well into the 19th century, it began to be introduced massively as a food source, for recreational fishing, and in ponds as an ornamental species. The increase in population caused the species to cross the threshold and begin to act as an invader.
It is an engineer species of ecosystems. It removes sediment to search for food, and in doing so, unearths the roots of pre-existing plants , turning a river of clear waters and lush vegetation into a murky, eutrophic environment. Carp tolerates cloudy waters well, where predators lose their ability to hunt due to reduced visibility. Waterfowl, unable to find food, are displaced.
Despite everything, wild carp populations are threatened in their native region, due to overexploitation and mixing with domestic varieties.
largemouth bass
It was probably one of the most unnecessary introductions, if anything . It was introduced in Spain for sport fishing in 1955. The largemouth bass ( Micropterus salmoides ) is a fish that can measure up to 40 cm, with powerful jaws. In its young forms, it hunts for crustaceans, insect larvae, amphibians, and small fish. The largest specimens can devour larger fish, small mammals and reptiles that enter the water, and even bite the legs of waterfowl , causing serious damage, and eat unsuspecting chicks that are floating.
It has a preference for the slower stretches of rivers, where waterfowl stop to feed. The impact on these birds, direct and indirect —eliminating prey— causes them to be displaced to other places where largemouth bass are absent.
florida tortoise
Who does not know that little turtle with the red spots on the sides of its head that was so sold in the 90s as a pet, that so many people had at home, that gave so many surprises when their owners realized the size and voracity of the animal. That caused so many people to end up releasing them into the natural environment.
Trachemys scripta is a species that alters the structure of the riverbed vegetation. It devours plants, invertebrates, fish, amphibians, small reptiles and mammals, and can even attack the eggs of birds that nest near the water. It competes for resources against the two native tortoise species, the Leper Pond Turtle and the European Pond Turtle. It grows larger and also produces more abundant offspring, and is more tolerant to pollution and human influence.
In addition, it is a Salmonella vector , so in some conditions it can pose a public health risk.
american mink
The American mink ( Neovison vison ) is probably the invasive mammal that has the most impact on Spanish rivers. It is a strong competitor that displaces other mammals such as the water vole, the stoat, the polecat and the European mink, to which it transmits the deadly Aleutian disease. It is a voracious predator capable of hunting crabs, amphibians, fish, bird eggs and small mammals such as the Pyrenean desman.
The American mink was the protagonist of sad stories of liberation of farm animals, with disastrous consequences. However, neither these releases were the origin of the problem, nor are they the main focus of the invasion. The real problem is, in fact, the mere presence of the American mink on peninsular soil and the inability to prevent these animals from escaping from time to time.
What do we do?
When the damage is done, you have to act quickly. However, when it comes to biological invasions, prevention is better than trying to exterminate. The best way to combat them is to act before they occur, through mechanisms for predicting invasive potential and preventing their introduction, and surveillance, early warning and rapid action systems when they are still incipient invasions. It will be the best way to avoid the invasion, and it will not be necessary to apply more drastic measures later.
REFERENCES:
BOE. 2013. Royal Decree 630/2013, of August 2, which regulates the Spanish Catalog of invasive alien species. BOE, 185 (Sec. I.), 56764-56786.
Lowe, S., Browne, M., et al. 2000. 100 of the world’s worst invasive alien species: a selection from the global invasive species database (Vol. 12). Invasive Species Specialist Group Auckland.
Oliva-Paterna, FJ, Ribeiro, F., et al. 2021a. List of exotic aquatic species of the Iberian Peninsula (2020). Life Invasaqua.
Oliva-Paterna, FJ, Ribeiro, F., et al. 2021b. List of potentially invasive exotic aquatic species in the Iberian Peninsula (2020). Life Invasaqua.
