Codium fragile is one of the most harmful invasive algae in coastal systems, as it is capable of displacing native species worldwide. In the northeastern Atlantic, its first records date back to the beginning of the 20th century, but, however, this species was not described in Spain until 1966, specifically in the Cantabrian Sea. Its success in the invasion process is mainly attributed to its wide physiological tolerance to both temperature and salinity, types of substrate or pollutants, as well as its rapid growth during the summer, low pressure from herbivores and the various modes of reproduction and dispersal, both sexual and vegetative or parthenogenetic. However, on the coasts of the Iberian Peninsula, several scientific studies have been able to demonstrate that the native species, C. tomentosum (on the right in photograph 1), was able to cope with the invasive species. Thus, in order to better understand the invasive nature of this algae, scientists from the Singular Center for Marine Research (CSIM-ECIMAT, University of Vigo) and the Rey Juan Carlos University are developing a study on an algae that, despite being native to Japan, is now distributed throughout the world. This study is part of the doctoral thesis of Ana García, who is currently carrying out a first experimental phase at the Toralla Marine Sciences Station (ECIMAT) under the auspices of a research project in collaboration with the researcher from the EcoCost group of the University of Vigo, Celia Olabarría.
The researcher from the Rey Juan Carlos University Ana García explains that “in previous studies carried out by our research team, we observed how the native species C. tomentosum and the invasive C. fragile (left in photograph 1) coexisted along the coasts of the northwestern Iberian Peninsula in the lower intertidal zone, in areas that included Bifurcaria bifurcata, and in the upper zone where intertidal pools are found”. However, compared to what happens in other regions, where a continuous dispersion of C. fragile was confirmed, in the northwestern peninsula the native species had a greater area of occupation and number of new individuals than the invasive species.
In this scenario, explains García, the need arises to evaluate the competition between and within the two species. To this end, the researchers have proposed an experiment in two phases; the first consists of a cultivation experiment under controlled conditions in the laboratory, which is being carried out at ECIMAT (photo 2); and the second phase will be carried out in the natural environment and will consist of subjecting the individuals obtained in the laboratory to different levels of stress, levels that will correspond to different tide heights and locations. Ana García says that in the first part of the experiment, the two species under study are being cultivated: C. tomentosum and C. fragile using different intraspecific and interspecific densities. “So far, the cultures have developed successfully and, shortly, it will be possible to tackle the second phase of the experiment in the natural environment.”
Codium fragile, a cryptic species
In recent decades, the number of biological invasions has increased in marine ecosystems, mainly in coastal systems, as a result of ballast water and aquaculture. The scientific community indicates that the main ecological impacts of these invasive species are competition with native species for resources; the displacement or disappearance of native species, reducing biodiversity and even causing local extinctions; and changes in community structure and in food chains and nutrient cycles. Invasive species are characterized by having a series of characteristics that give them the ability to better adapt to the new environment, such as vegetative reproduction, large size, rapid growth cycles and broad tolerance to environmental factors. However, the researcher recalls, “the number of invasive species may be underestimated by the presence of cryptic species”, those that are morphologically indistinguishable from native ones. The species C. fragile is an example of this situation, since it is “morphologically identical to the native species C. tomentosum and C. vermilara”.
Invasive species and climate change
The increase in the number and distribution of exotic species is closely linked to the climate change process, since the role of climate in the distribution of species is fundamental and the increase in temperatures as a result of global change favors the appearance, establishment and dispersion of exotic species, which can be potentially invasive, if they are capable of displacing native species. García explains that in this climate change scenario “numerous works have observed contractions and expansions in the distribution of species and, on our coasts, we can find some examples such as the case of species with an affinity for warm waters such as Fucus serratus or Zostera noltii, which are in a phase of retraction, while others from warm waters, such as C. fragile, are in a phase of expansion. “Both casuistries together, invasive species and climate change, are two of the greatest threats to biodiversity, since in this scenario, species originating from warm regions can increase numerically and spatially, generating large populations, which will spread over large areas. Furthermore, this warming may prolong the duration of the occasional occurrence of initial introductions due, on the one hand, to the increase in the frequency of invasion processes and, on the other, to the increase in suitable habitats.
