Experts of the UB warn about the ecological impact of the invasive alga rock snot on peninsular rivers

The new research study conducted by this team, members of the Research Group Freshwater Ecology and Management (FEM) of the UB, is the most complete one so far regarding ecology of systems on this exotic alga, and together with previous studies by this team, it builds a strategic tool to control the proliferation of the species and prevent its presence from appear in river areas where there is no sign of it yet.

The Didymosphenia geminata alga, or rock snot, is a freshwater exotic and invasive species that can cover kilometres of riverbeds. This diatom comes from northern Europe and North America and lives in clean and cold waters without phosphor, and it creates big biomasses that alter the biodiversity and functioning of fluvial ecosystems. D. geminata resists dehydration and can survive outside the water in extreme temperature and humidity conditions. Detected in more than fifty countries in tempered and cold areas, this alga has caused critical episodes in New Zealand and the United States, where it has affected the migration of species of economic interest such as the salmon.  

An invasive alga conquering the less polluted rivers

“The special feature of the rock snot is that, unlike many algae ─that grow when there is more phosphor in the water─, this one can proliferate in oligotrophic conditions (no phosphorous), favoured by a small rise of temperatures or insolation (for instance, in rivers without gallery forests)”, says Narcís Prat, professor from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB and head of the FEM Group.  

“When water growth speeds up -continues Prat- a kind of snot is created and it sticks to the river stones. This thick layer of algae alters the habitat of many organisms that lived on these stones (snails, insects, etc.). The effects of the massive growth of the D. geminate are also affecting fish such as the trout, which has less feeding options and lay its eggs. As a result, there are only some small organisms that can live in the area where the rock snot is”.

From canoeing to recreational fishing: this is how an invasive species spreads around

There are more and more massive episodes of this alga, which was first detected in the Iberian Peninsula by the UB Professor Ramon Margalef during the fifties. Activities such as canoeing, recreational fishing and hiking favoured the accidental dispersal of the alga in many rivers. At the moment, the basins of the Ebro and Duero rivers, in the north of the Iberian Peninsula, are the most affected ecosystems by the massive proliferation of D. geminata.

The new study conducted by the FEM Group of the UB assesses the effects of the invasion of this alga in the natural habitat and its referent is Lumbreras River, in the Ebro River basin in la Rioja. “This is one of the most affected areas in the Peninsula due the massive growth of D. geminata since 2011”, says the lecturer Joan Gomà. “In this area in particular, there are the perfect environmental conditions -hydrological regulation, low temperature, low phosphate content and lack of gallery forest- to boost the massive proliferation of this invasive alga”. 

According to the researcher Rubén Ladrera, first author of the article, “regarding the Ebro River, the most severe episodes affect the Pyrenean rivers (mainly Cinca, Ara and Subordán, in Huesca), and regarding the Iberian system, the basins of Iregua and Najerilla, in la Rioja, are the most affected ones.

“There is not a record for massive growth with environmental impact for the rest of Catalonia -adds Ladrera- but we should watch out to reduce the vulnerability of the ecosystems towards these invasive episodes”. 

How can we fight the alga proliferation?

Preventing the alga from spreading and controlling the intensity of massive growth will be crucial to stop the species from getting to new places. In this context, research studies by the group FEM will help identify the episodes of proliferation and determine the environmental factors that boost the algaʼs growth in peninsular rivers.

“It is impossible to get rid of these populations completely”, highlights Rubén Ladrera. “Therefore, we need to clean with lye all materials that have been in contact with D. geminata (fishing gears, boots, canoes, etc.) to prevent the alga from spreading in other rivers. Since sometimes the alga is not seen easily -despite having a high cell density- some cleaning protocols are needed after being in contact with any water ecosystem so that we can avoid the D. geminata transmission as well as other invasive species”.

Controlling the public uses of the affected areas and promoting social awareness and environmental education are necessary tools to prevent the environmental footprint of these species in peninsular rivers. It is also important to design control programs for the affected areas and those that show ideal conditions for the species. The basins in which the rock snot has been erased need a restoration of gallery forestsʼ plants to reduce the levels of insolation on the river beds (that is, restricting the photosynthetic activity and production of algae filaments).

The new study, published in the journal PLOS ONE adds more knowledge to the works by the FEM Group ─with the distinguished contribution of the UB lecturer Maria Rieradevall─ that continue the research studies that were started by the ecologist Ramón Margalef (1919-2004), a model for generations of ecologists and naturalists in Spain and founder of the Department of Ecology of the UB in 1967.  

Naturalizing the hydrological cycle of rivers

Invasive species are one of the biggest threats to the conservation of biodiversity in water ecosystems worldwide. In countries such as New Zealand and the United States, there have been many studies to control the population of D. geminata with phosphate or cooper-based biocides, products that can also affect natural ecosystems. Other in-study strategies to fight the invasive species could be the certain increase of phosphate content in rivers or the release of -warmer- water surface layers in reservoirs -which are less suitable for the biology of the species. 

In this context, hydrological regulation, which completely alters the natural river flow, is a factor that favours the proliferation of invasive species over the autochthonous ones. “Naturalising the hydrological cycle of rivers is a way to help the population control of the alga. If there are extreme flows -in autumn and winter- we could drag algae filaments and cells right before the most active period of the species, which starts in late spring”, concludes the UB research team. 
 

Images: Rubén Ladrera and Joan Gomà (Faculty of Biology and the Water Research Institute-IdRA)