A team of Galician researchers has been studying changes in the distribution of gastropod mollusks on the Atlantic coast of the Iberian Peninsula for several years. Their initial objective was to create a map of the distribution of species today in order to compare it with data from decades ago and determine the advances and declines of populations. After completing this stage, a new process has now begun, focused on finding data that links these population changes to climate change. Professors from the University of Vigo Marcos Rubal and Jesús Souza Troncoso are collaborating on this project with Puri Veiga, from the University of Santiago de Compostela, and Juan Moreira, from the Autonomous University of Madrid. They explain that this project was born in 2010 when, while working on other studies, they detected some species of gastropods that were not common in Galicia. In 2011, they launched a specific investigation that included sampling from southern Portugal to the Lugo Sea “to have a general idea of the distribution of these species, which are mainly snails”. Thanks to this field work, they now have a global view of the distribution that allows them to identify changes in it, and thus select six species in which substantial changes in distribution were detected to study them in detail: three cold-water boreal species that were retreating and three tropical species that were beginning to appear in areas where they were not common.
The data obtained in the first phase of the work precisely confirm that the three boreal species are becoming less abundant and are retreating northwards, until they disappear from areas where they were common decades ago. On the contrary, the tropical species, which were previously only found in the south of Portugal, are now present in large numbers in a large part of the Cantabrian coast. Marcos Rubal explains that these changes are very significant because “the Iberian Peninsula is a border, a space of change, the northern limit of many subtropical species and the southern limit of those of cold boreal waters and that is why it is here where the changes are first noticed”. From this point forward, they are faced with the challenge of obtaining scientific evidence that relates this phenomenon to climate change and they highlight that “everything points to this being the case, but many factors may be at play that cause these changes and we must determine to what extent each one acts”.
Lack of knowledge about common species
The researchers point out that they are in an initial stage of the study, which is being developed in parallel with the research projects of their groups, but they have already published several scientific articles advancing some of the results in journals such as the Journal of Sea Research or the Journal of Experimental Marine Biology and Ecology. They point out that one of the main drawbacks they have encountered is the surprising lack of biological information on species as common and well-known as snails or lapras. “There are studies of the species in other places, such as the United Kingdom or the Netherlands, but not in Galicia and, given that the conditions here are different, knowledge adapted to the environment is necessary, which however does not exist”. Therefore, their work is progressing in parallel in this direction, to expand knowledge of the basic biology of these species.
Advancement of subtropical species and retreat of boreal ones
The latest sampling work they did covered from Ribadeo to Sagres, in the south of Portugal, which includes 170 beaches. “In each of them we measured the abundance of the six species, the three tropical and the three boreal, and we see how the subtropical ones, absolutely all of them, have increased their distribution range”. In fact, they detected that one of the three tropical species they are studying (Siphonaria pectinata) in 1917 only appeared in the Strait of Gibraltar and the south of Portugal and in 1940 it was already in Buarcos, near Coimbra. In recent sampling, Veiga explains “we have already found it in Arteixo and in very good conditions, with different sizes, with eggs and reproducing”. The other two tropical species they are working with have, unlike the previous one, a discontinuous distribution range, that is, they appeared from Gibraltar to near Setúbal, but also in the Basque Country and Cantabria. Currently, Phorcus sauciatus has already colonized the entire coast, except for a stretch between Porto and Peniche, while the third of them, although its presence in the south has not increased, in the north of the peninsula it has spread strongly, reaching from the Basque Country to Ferrol.
The species of cold-water gastropods, on the other hand, are in decline. In these works, the researchers focused on three Littorina saxatilis, Littorina littorea (snail) and Nucella lapillus. These three species, the researchers highlight, “have their distribution limit in the south of the Iberian Peninsula but we have not found stable populations, for example from Nucella, to Lisbon”. The case of Littorina saxatilis is similar, since in the Lisbon area it is only present on one beach, while Littorina littorea has completely disappeared as far as Óbidos.
Factors, consequences and relationship with climate change
The team of researchers is now working with specific experiments that will allow them to determine what conditions cause these changes, such as water temperature, salinity, etc. Everything seems to point to climate change and they highlight the scientific evidence that water has warmed, “but global change is much more than temperature, ocean acidification, changes in currents, exposure to waves, etc. also influence.”
The scientists also highlight the consequences that these changes in population patterns can have on ecosystems. They give as an example the case of Stramonita haemastoma, a subtropical species similar to a Nucella but 20 times larger, which is therefore capable of eating 20 times more mussels and altering the ecosystem. “It could have a quite radical effect if it establishes itself here, both because it could destroy resources and because it would displace native species,” they recall. They also emphasize the small isolated populations of certain species that resist in the south thanks to a microhabitat. “In the event of a future climate reversal, they could be responsible for recolonizing the habitats that were once theirs,” provided they are genetically rich and can resist and recolonize. Conversely, if they are genetically poor, any other disturbance, such as a spill, could make them disappear, they conclude.
Source: duvi
