Lantern fish threatened by mercury?



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Lantern fish threatened by mercury?

The abyssal environment, according to the ecological classification of ecosystems, starts from about 200 meters deep, where, in general, there is the end of the continental slope and the beginning of the abyssal plain and where the quantity of light that arrives is no longer sufficient to support the chlorophyll photosynthesis of plants.

The ecosystem of the deep sea is therefore completely dependent on the rain of waste and organic substances that descend from above. At even deeper depths, in the dark and lack of food are added very high pressures (the pressure increases by 1 atm every 10.33 meters of depth), cold (the temperature at the bottom of the oceans rarely deviates from 0 ° C) and the very low population density, which makes it difficult for the sexes to meet during the reproduction period.

On the other hand, the deep sea environment is extraordinarily stable, with absolutely constant temperatures throughout the year. The lantern fish is one of the inhabitants of these abyss, but it seems that its ecosystem is threatened by the mercury dispersed in the ocean.

The article: Main drivers of mercury levels in Southern Ocean lantern fish Myctophidae, published on the Environmental pollution, explained: "Myctophids are the most abundant fish group in the Southern Ocean pelagic ecosystem and are an important link in the Antarctic marine food web.

Due to their major ecological role, evaluating the level of mercury (Hg) contamination in myctophids is important as a step towards understanding the trophic pathway of this contaminant. The concentrations of total Hg were determined in muscle, gill, heart and liver tissue of 9 myctophid species to quantify tissue partitioning variability between species.

Organic Hg concentration and proportion in muscle was also determined. Hg concentrations were higher in the liver and heart than in muscle and gills, but the proportion of organic Hg was almost 100% in muscle, indicating that the main uptake route for Hg is through the diet.

Most of the species analyzed have similar vertical and horizontal distributions, and similar feeding modes and prey. Geographical and temporal variability of Hg concentrations was examined using samples from 3 different sampling cruise (2007/08, 2015/16 and 2016/17) and 2 locations (South Georgia and South Orkneys Islands).

Our results appear to indicate a decreasing trend in Hg contamination over the last decade, particularly gill tissue, which is in agreement with a previous study on squid from the same region. There was no significant variability in Hg concentration between the different sampling locations.

Hg levels were consistent with values ​​reported previously for myctophids around the world, indicating low global-scale geographic variability. A positive relationship between fish size and Hg concentration was found for most species, with the exception of Electrona antarctica females, which may be explained through Hg elimination by egg laying.

We estimate that myctophids collectively comprise a Southern Ocean mercury 'reserve' of ≈1.82 metric tonnes."