Home Sciences A massive suffocation of fish stalks the Mar Menor

A massive suffocation of fish stalks the Mar Menor

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The Mar Menor is threatened with a new episode of suffocation of marine species, due to the lack of oxygen resulting from the nutrients derived from the crops that surround the lagoon: the waters are filled with algae and microalgae that prevent photosynthesis and trigger the catastrophe ecological.

Due to the recently recorded climatic anomalies, the potential risk of a new episode of oxygen depletion and massive mortality of organisms in the Mar Menor is very high, warns the Spanish Institute of Oceanography in a report.

It highlights that the climatic anomalies that occurred during the month of March, characterized by the highest levels of humidity in the last 62 years, as well as by two episodes of intense hazemay have significant effects on the ecosystem of the Mar Menor during this summer.

He adds that these climatic events provide massive amounts of nutrients, both nitrogen and phosphorus, from the crops that surround the area, which can cause an oxygen deficit in the lagoon system and the death of marine organisms that inhabit the Mar Menor.

Any global and partial analysis of the state of the lagoon must be contextualized in the eutrophication process that the coastal lagoon has been experiencing over the last few decades, the authors point out in their report.

The agricultural activity, in the origin

They add that this process originates as a consequence of the massive and almost continuous contributions of nutrients from agricultural activity, which enter the lagoon through surface runoff, groundwater, dragging of water by torrential rains and pluvial collectors. To all this we must add the pollution derived from the haze.

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The immediate consequence of these processes is the proliferation of fast-growing algae, many of them microscopic unicellular algaewhich reduce the light that reaches the bottom of the lagoon and limit the photosynthesis that bacteria that live under the surface can carry out.

Algae blooms also increase oxygen consumption overnightwhen photosynthesis is not possible, causing a shortage of air that ends up suffocating the marine species present in the Mar Menor.

The Institute highlights that a sharp increase in chlorophyll has already been registered, a clear indication of the existence of a large quantity of phytoplankton and other algae, which do not let light through and cause episodes of oxygen crisis.

controlled chlorophyll

The report adds that, although chlorophyll levels are still lower than those recorded in previous episodes of explosive phytoplankton development, their rising trend it is likely to continue in the coming weeks and months, as the light and temperature increase corresponding to this time of year.

It concludes that the nutrients contained in the surface runoff caused by intense rains, together with those contained in these groundwater contributions, form a perfect cocktail with the increase in temperature and solar radiation characteristic of the winter-summer period, which promote the rapid growth of this type of opportunistic species, the clearest exponent of the eutrophication process that the lagoon has been experiencing for decades.

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Due to these algae developments, the potential risk of a new episode of oxygen depletion in the Mar Menor has increased, states the report.

normal for now

It also highlights that, despite these episodes of intense and prolonged rains, neither salinity nor temperature have so far shown significant differences between the most superficial layers of the water column and the deepest and closest to the bottom, which rules out the existence of hydrographic stratification structures such as those described in a previous episode of torrential rains, likely to cause severe oxygen deficits in the deepest areas.

In fact, there has been no deviation from the pattern of seasonal oxygen variation, not even in the deep water layers of the Mar Menor, the report states.

The mean values ​​of redox potentialwhich indicates the sanitation of the water, are at the moment normal, within the ranges recorded in previous samplings in situations of well-oxygenated waters and without accumulations of reduced carbon, nitrogen or sulfur compounds, product of the anaerobic decomposition processes of matter organic, concludes the study.

Reference

Ruiz, JM, Clemente-Navarro, P., García Muñoz R. Progress report (April 2022) of the Monitoring Program for the Ecological Status of the Mar Menor. Oceanographic Center of Murcia, IEO-CSIC, 13 pp.

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