Sunday, August 7

Anoxia, toxicity and high temperatures in the Mar Menor: the factors that could have killed thousands of fish according to the Oceanographic Institute

Experts from the Spanish Institute of Oceanography (IEO, CSIC) are analyzing the scientific evidence available in relation to the causes of the new mass mortality event that occurred on August 15 and 16 in the Mar Menor, including its origin as a result of oxygen deficiency both in water and sediment.

The Government of Murcia will denounce Minister Ribera for “allowing the entry of nutrients and fresh water into the Mar Menor”

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From the IEO they indicate that mortality has occurred in animals belonging to a wide variety of species -especially fish and crustaceans- that develop their activity on the bottom or very close to it, but of predominantly small size with less escape capacity and, therefore, “more vulnerable to stress factors such as temperature, anoxia or the toxicity of some type of pollutant”. Experts insist that none of these factors and their multiple interactions can be ruled out a priori “without having more evidence, temperature being only one among the various factors that may have led to this event.”

As was shown in the report presented by the IEO in July 2020, both the average water temperature and the frequency and intensity of extreme heat events have maintained an increasing trend during the last decades. It is, therefore, to be expected that this factor contributes to the deterioration of the Mar Menor and hinders its recovery. However, according to the Spanish Institute of Oceanography, the organisms that inhabit this type of lagoon ecosystems are especially adapted to sudden and fluctuating environmental changes, so “it is difficult for them to be affected by a slight increase in temperature, within of the characteristic summer maximum of the Mar Menor “.

On the other hand, the previous alteration that the Mar Menor undergoes due to eutrophication (promoted in turn by the entry of nutrients through surface or groundwater) decreases its resilience, that is, its ability to resist alterations such as those that can cause heat stress from a heat wave or another factor, experts say.

“In accordance with the above, any diagnosis of the Mar Menor and of the causes that have triggered this new event must be carried out from the scientific rigor provided by the exhaustive analysis of the existing evidence” indicate the IEO. Scientists from the Oceanographic Center of Murcia, experts in the study of the lagoon for decades, carry out continuous sampling that has made it possible to capture some basic data on the days in which this last episode occurred, and are currently analyzing the available evidence to shed light on the causes and consequences of this new fauna mortality event in the valuable hypersaline lagoon.

In the resolution of cause-effect relationships in the face of these extreme events or the existence of associated trends, for example climate change, experts consider that it would be highly facilitated by creating infrastructures that allow continuous and real-time monitoring of the environmental properties (temperature, oxygen or chlorophyll concentration, currents …) of the lagoon.

Regarding the role of temperature, he considers “very hasty to attribute to this single factor the massive death of fauna without carrying out a more detailed analysis of long-term time series of this variable, which allows us to check if it is some type of significant thermal anomaly , capable of causing the death of organisms “. For years the IEO has maintained a network of submersible temperature sensors both in the Mediterranean and in the Mar Menor and at the moment the experts are analyzing the time series since the 1980s to check if there is any extreme and significant event that explain this mortality alone.

What is the IEO?

The Spanish Institute of Oceanography (IEO, CSIC), is a National Center of the Higher Council for Scientific Research (CSIC), dependent on the Ministry of Science and Innovation, dedicated to research in marine sciences, especially in relation to scientific knowledge of the oceans, the sustainability of fisheries resources and the marine environment. The IEO represents Spain in most of the international scientific and technological forums related to the sea and its resources. It has nine coastal oceanographic centers, five marine culture experimentation plants, 12 tide stations, a satellite image receiving station and a fleet made up of four oceanographic vessels, among which the Ramón Margalef and Ángeles Alvariño stand out.