Praia Ladeira in A Ramallosa, Nigrán; Arnelas and A Cantareira, on the Island of Arousa and Mañóns in Boiro. These are the four beaches chosen by researcher Marina Gómez to carry out her doctoral thesis, a pioneering investigation into the ecology of macroalgae strandings on estuarine beaches on the coast of Galicia, what are known as protected beaches or beaches with little exposure to waves. The results obtained leave no room for doubt: most of the biodiversity of these beaches depends largely on the stranding and decomposition of algae that the force of the tide deposits on them.
“Algal deposits provide not only a physical structure that can be used as a refuge or breeding ground, but also represent an important source of nutrients and energy for beach fauna,” explains the author of the thesis, who for more than two years studied in detail the quantity, location and specific composition of the algal deposits that arrived at these four Galician beaches. She did this as a researcher in the Coastal Ecology research group, to which the two directors of the thesis, professors Mariano Lastra and Jesús López, belong.
The selection of these four enclaves was not done randomly, but based on their physical characteristics (for example, the degree of protection from waves) and their biological characteristics (presence of bivalve mollusc banks, among others). “What I did was to analyze the effect that these algae contributions have on the biodiversity of the beaches and determine which species of macrofauna are associated with the degradation processes that they undergo once deposited in the sand,” emphasizes Gómez, while clarifying that the research included a field experiment in which this degradation process was analyzed in detail.
The degradation process affects all organisms in its environment.
The results of the thesis show that the arrival of algae is the basis of a complex trophic system that provides different pathways for the transformation of nutrients, from external contributions of algae to primary and secondary consumers (crustaceans, insects, etc.) and even higher up the food chain (fish, seabirds and even dune reptiles). “The respiration values measured on the algae patches have proven that these deposits create an active zone or hot spot with a biological and chemical activity that is especially different from that of its surroundings”, points out the author of the thesis, who explains that this indicates that the processes that occur during the different phases of the degradation of all this plant material produce cascade effects that affect their entire environment and the associated organisms. “They are a whole series of details that highlight the role that these accumulations of macroalgae have on the functioning of the ecosystem”, emphasizes Gómez.
Between ecological and economic interests
The Coastal Ecology group, under which this research was carried out, has extensive experience on the role of algae on ocean beaches, directly exposed to the waves, but until now there was hardly any information on this type of protected beaches, which are of great relevance in Galicia, both because they are very numerous, “a good part of our beaches are within the estuaries and, therefore, protected from the direct action of the waves”, and because of the type of activities that are carried out on them, linked to tourism or traditional activities such as fishing or shellfishing.
“On a large part of the protected beaches of our coast, important economic activities are carried out, such as the extraction of bivalve molluscs, with a high number of shellfish gatherers working on the beach,” emphasizes the researcher, who explains that one of the main conflicts that arise in these shellfishing areas is the accumulation of algae, which in many cases tend to occur massively at certain times of the year and which are related to the processes of upwelling of deep waters that occur on the coast and that fertilize the environment. “Furthermore, in these sheltered and wave-protected environments, the optimal conditions for the growth of what are known as ‘opportunistic algae’, such as sea lettuce or sea urchin, which favors the formation of dense accumulations of algae that are left floating adrift and that, generally, end up stranded on the beaches,” explains Gómez, who emphasizes that this phenomenon, which is usually known as green tide, is a problem for bivalve mollusc banks, since they cover the surface of the sediment during low tide, causing the molluscs to die from suffocation, “which is why the elimination of these deposits is a widespread practice.”
Given the existence of this conflict between economic and ecological interests regarding the management of these seaweed strandings, the author of the thesis defends as “vitally important” having the necessary knowledge to address this problem and establish plans for the conservation and management of protected beaches.
Source: Duvi http://duvi.uvigo.es/index.php?option=com_content&task=view&id=11306&Itemid=2
