Mercury (Hg) is a toxic metal, which as seen its concentrations increase in the environment due to anthropogenic activities. It bioaccumulates in organisms throughout life and biomagnifies in food webs, reaching high concentrations in some top predators. To understand the threat of Hg to these predators, monitor Hg concentrations in organisms at intermediate trophic levels it is essential, as they are crucial factors in the trophic transfer of Hg. But how do we monitor Hg in elusive species such as Southern Ocean squid? The answer lies in their beaks, which are chitin structures resistant to digestion, that accumulate in the stomachs of predators and can be collected in regurgitations or after the animal’s death.
One such squid species, Moroteuhopsis longimana, inhabits the deep waters of the Southern Ocean and can reach more than 2 meters in total length. It bioaccumulates Hg throughout its life and is an important prey item for several top predators such as seabirds, marine mammals and fish, so understanding its role in the transfer of Hg in the food web is crucial. However, there is still a lack of knowledge about the relationship between Hg concentrations in M. longimana beaks and muscle (the main tissue consumed by the predators), which this study aims to analyse.
To do that, 21 buccal masses of M. longimana collected from the stomach of the Antarctic toothfish (Dissostichus mawson). For total Hg analysis, the upper and lower beaks were sectioned into the wing (W) and hood tip (H), and the remainder of the lower (L) and upper (U) beaks (Figure 1). A portion of the buccal mass muscle (M) was also collected for analysis.
Results showed that Hg concentrations in the muscle are ~100 times higher than in the whole beaks (U and L) and ~50 times higher than in the W and H sections (Figure 2). Inter-tissue variability in Hg concentrations confirms that the concentration of Hg in the beak does not reflect directly those in the muscle.
However, a positive relationship was found between Hg concentrations in the wing (W) and muscle (M), translated by the following equation:
Hgmúsculo = 34.88 Hgasa + 0.12
This equation suggests that mercury concentration in the wing can be used as a proxy for Hg concentration in the muscle of M. longimana. However, it should only be used for adult individuals, as this study only used fully chitinized adult beaks.
Future studies can now use this equation to estimate the Hg concentration in the muscle of other M. longimana, through the analysis of the Hg concentration in the beak wing, providing a means of assessing the levels, transport and fate of Hg in within Southern Ocean ecosystem.
Source: Lopes-Santos S, Xavier JC, Seco J, Coelho JP, Hollyman PR, Pereira E, Phillips RA, Queirós JP (2025) Squid beaks as a proxy for mercury concentrations in muscle of the giant warty squid Moroteuthopsis longimana. Marine Environmental Research 204:106841.
Author: Sara Santos
