An army of 60 million oysters to decontaminate the Mar Menor

What man has ruined, let an oyster solve. Or at least, let him help fix it. This could be a basic summary of the RemediOS scientific project, a strategy led by the Spanish Institute of Oceanography (IEO-CSIC) with the aim of improving the water quality of the Mar Menor through the use of bivalves, which would eliminate nitrates thanks to their great filtering capacity.

After considering other species at the beginning of this bioremediation proposal -year 2016-, such as clams and cockles, the researchers have decided on the flat oyster (‘Ostrea edulis’), a mollusc that came to have 135 million specimens in the lagoon thirty years ago. Currently there are only a few hundred left, 1,000 or 2,000 at most, the main promoter of this nature-based solution explains to LA VERDAD,
Marina Albentosahead scientist of the IEO-CSIC at its headquarters in Lo Pagán (San Pedro del Pinatar).

“Along with the shellfish, the flat oyster entered the Mar Menor in the seventies of the last century, when the Estacio channel was opened and the physical-chemical conditions of the Mar Menor changed”, recalls this bivalve physiologist, who has woven a important network of contacts with other European and North American experts who already work with this species in the North Sea, the United States and Australia.

Seasons

experimental

of filters

CAN-Center

of Activities

Nautical

(Lo Pagan)

Yacht Club

Minor Sea

(The Alcazars)

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CNN-Nautical Club

The grandsons

(Cartagena)

1. In water: the structure of the platform would contain anchor points for housing devices for the bivalves.

2. On the surface: place where the physiological determinations will be carried out in situ.

3. In the air: they will have informative panels aimed at educational centers and society.

Release

veliger larvae

(170µm)

larva

pediveliger

(230-250µm)

Seasons

experimental

of filters

CAN-Center

of Activities

Nautical

(Lo Pagan)

Yacht Club

Minor Sea

(The Alcazars)

CNN-Nautical Club

The grandsons

(Cartagena)

Release

veliger larvae

(170µm)

1. In water: the structure of the platform would contain anchor points for housing devices for the bivalves.

2. On the surface: place where the physiological determinations will be carried out in situ.

3. In the air: they will have informative panels aimed at educational centers and society.

larva

pediveliger

(230-250µm)

Captive breeding

There is hardly any data on the decline of the flat oyster in the wetland: there are records from the San Pedro Fishermen’s Association for the 1982 and 1985 fisheries: 80 and 140 tons, respectively. There is no evidence of a commercial extraction after those years. It is known that it was difficult to collect them and that the extensive meadow of ‘Caulerpa prolifera’ could negatively affect them, which apparently “asphyxiated” them.

According to very preliminary calculations, sixty million oysters would be needed for their filtering function to have a positive effect on the polluted waters of the Mar Menor, affected by a process of eutrophication after four decades of urban and agricultural discharges.

Albentosa also makes it clear that the oysters would play a complementary role “within a comprehensive action plan that must include the elimination of land discharges.”

In the IEO-CSIC laboratories in Lo Pagán they already have ten oysters and they hope to reach a hundred, collected in the vicinity of Barón Island. The idea is to reproduce them in captivity, control their evolution there in tanks until they reach between two and five millimeters, to later transfer them to facilities located in the Salinas de Marchamalo (La Manga, Cartagena), where they would remain adapting to the marine environment until reaching the size of one centimeter.

Then the critical moment would arrive to transfer the small oysters to the Mar Menor. According to the initial forecasts, variable depending on the evolution of the project and the available budget, they would initially be established in three points of the lagoon –Lo Pagán, Los Alcázares and Los Nietos–, where auxiliary floating platforms designed by Clavel Arquitectos would also be installed. The ‘Ostrea edulis’ reaches its maximum size, between 10 and 11 centimeters, after two years.

“It’s not just about recovering a species, but also a habitat,” explains Marina Albentosa. “Because the flat oyster is an engineering species: it is the first link in the ecosystem that is to be restored, and biodiversity will be generated around the reefs that it forms because the fish will take refuge there and consequently the catches will increase.” Nature coming to the aid of nature.

inedible

The commercial use of the Mar Menor flat oyster would still be a long way off, warns Marina Albentosa: it could not be eaten due to the poor quality of the water, “but later who knows, once the level of contaminants has been analysed.”

Pearls are not to be expected either – this species does not produce them – although the environmental service they could provide is a gem: removal of nutrients from the water, fixation of CO2 in the valves and obtaining calcium carbonate from their shells.

Marina Albentosa emphasizes that RemediOS is “a project that arises from scientists and that brings together social organizations and the administration.” In addition to the IEO-CSIC –through three of its offices, those of Lo Pagán, Vigo and the Balearic Islands–, the Association of Naturalists of the Southeast (ANSE), the Institute of Marine Sciences of Barcelona (ICM-CSIC), the Fundación Estrella de Levante and the universities of the Basque Country and Dalhousie (Canada).

The Biodiversity Foundation – an agency of the Ministry for the Ecological Transition and the Demographic Challenge – provides the financing –172,000 euros through the Pleamar program, with FEMP funds– and the General Directorate of the Mar Menor (Ministry of Water, Agriculture, Livestock, Fisheries and Environment) has collaborated by paying for the genetic study of the oyster, in charge of the University of Santiago de Compostela, and the design of the platforms.