In the innermost part of the Vigo estuary and the Pontevedra estuary, Mytilus galloprovincialis used to be the only mussel species. Since the introduction of the New Zealand pygmy mussel (Xenostrobus securis), the native species seems to be being displaced in the inner parts of these estuaries. This scenario is what Ignacio Gestoso studies in his doctoral thesis, under the supervision of Professor Celia Olabarria, from the University of Vigo, and co-supervised by Francisco Arenas, from the Interdisciplinary Center for Marine and Environmental Research, from the University of Porto. The research has as its final objective to evaluate the distribution and invasion mechanisms of the mussel X. securis, as well as the impact that the establishment of this species has on the benthic fauna associated with mussel beds.
The results show that X. securis is spreading in both the Vigo and Pontevedra estuaries, although for the moment the highest abundances are concentrated in the inner part of both estuaries and decrease significantly with the increase in salinity towards the middle part of the estuaries. Gestoso explains that “the project ranged from sampling and monitoring in the estuaries, to manipulation experiments both on the coast and in the laboratory”. This work included a three-month stay at the CIIMAR facilities in Porto, which allowed part of the experimental studies related to the effects of climate change to be carried out.
The reasons for the expansion
Gestoso’s thesis documents the invasion process of X. securis in the Rías Baixas with the aim of obtaining an overview of the changes that are occurring in the resident community due to the introduction of this foreign species. With the combination of observations made in the environment and manipulation experiments both on the coast and in the laboratory, an approximate knowledge of the current moment of the invasion process, its impacts on the native community and possible trends in a future climate change scenario has been achieved. The researcher points to salinity as the main factor for the invasive mussel to be found mainly in the interior areas of the estuaries, since it “determines to a greater extent the abundance pattern of the species in the estuaries”. However, the establishment of groups or pines of the pygmy mussel in the inner part of the estuaries “is causing changes in the benthic habitat of the rocky intertidal, causing variations in the abundance of the dominant species”. The researcher also highlights that the different biological activity of the invasive mussel, such as different filtration rates, “may be promoting changes in the biosedimentary layers, which could indirectly affect the fauna that inhabits the sediment.”
Another effect of this invasion is that predators have a certain preference for the native mussel. Gestoso explains that evidence has been found that suggests that “the presence of abundant populations of the native mussel in the innermost part of the estuaries could favor the survival of the individuals of the invasive mussel by partially compensating for the negative effect of predators”, that is, that the Galician species would be allowing greater success in the establishment of non-native populations in the estuaries. Furthermore, the researcher adds that the work done with a key predator in the system such as the horn (Nucella lapillus) seems to indicate greater consumption of the native mussel, which could also indirectly contribute to the success of the invasion.
The invasive species, more resilient to climate change
Another of the main objectives of Ignacio Gestoso’s thesis is to explore future scenarios in which climate change could influence the invasion process of this species. The experimental work he carried out showed that changes in the temperature and pH of seawater as a consequence of anthropogenic climate change, “can alter the response of mussels both at the individual and population level”. Both species studied responded differently to these changes, with the invader generally having greater resilience than the native M. galloprovincialis to changes in temperature and/or pH. Thus, the scientist explains, “in a future climate change scenario, X. securis could have some physiological advantage that would allow it to become progressively more dominant over M. galloprovincialis in the invaded area”.
Future lines of action
Based on the work carried out by Ignacio Gestoso in this area, a series of future lines of action and research are opened. The scientist particularly highlights the need to carry out “a monitoring program of the populations of both species of mussels, at least in the Rías Baixas of Galicia, carrying out spatio-temporal sampling, that is, at different points along the coastline and over time”. He underlines that it would be important to achieve greater interaction between researchers and the different sectors or socio-economic activities that may be affected, as a key tool to be able to adopt effective management measures both in this case and in other environmental problems.
