Elements in Soft Tissues of the Young Mediterranean Mussel Mytilus galloprovincialis Lam. 1819 Collected in Sevastopol Bay (Crimea, Black Sea): Effects of Age, Sex, Location, and Principal Morphometric Parameters

Simple Summary Mussels accumulate trace elements in their soft tissues to levels several orders of magnitude higher than in the environment. For this reason, they are regarded as good trace element pollution bioindicators. Yet, there is limited understanding regarding which characteristics of mussels exhibit the strongest correlation with element accumulation. Furthermore, it remains unclear on what minimal spatial scale the differences in accumulation can be observed. We studied the effects of several biological characteristics on the contents of 72 elements in the soft tissues of mussels sampled from Sevastopol Bay. We found that most of the contents decreased with age, which was consistent with the decrease in the intercellular water content. There were significant differences in the element accumulation patterns in mussels from different sites of this relatively small water body, and multivariate statistical methods allowed distinguishing individuals sampled from each particular site. Sex differences did not significantly affect the overall element accumulation. Most elements demonstrated significant correlations as a function of only two gravimetric parameters, namely the ratio of soft tissue dry weight and the total weight of the mollusk. The results obtained contribute to understanding elemental biochemistry and aging in mussels and are of interest for improving mussel biomonitoring programs. Although the mussel Mytilus galloprovincialis has been known for decades as an excellent bioindicator of trace element pollution in the marine environment, there is still no information on the effects of a suite of its principal morphometric parameters and age on trace element levels in soft tissues. In this work, using inductively coupled plasma mass spectrometry, we studied the contents of 72 elements in soft tissues of M. galloprovincialis aged 0.5-4, which were sampled at three stations within a relatively small water body, Sevastopol Bay. Significant effects of age and sampling location on the element contents and soft tissue dry-to-wet weight ratio were discovered. The effects of sex were not significant. It was presumed for the first time that the decrease in element content in the soft tissues of young mussels can be associated with the decrease in physiological needs for elevated contents of essential elements and intracellular water with age. Combinations of six principal morphometric parameters showed that a function of as few as three parameters (soft tissue dry weight, whole mollusk weight, and shell height, with by far the greatest contribution of the dry-to-total weight ratio) formed significant correlations with the contents of the largest possible number of elements (69-88% of the total number). For the first time, it was shown that linear discriminant analysis and canonical analysis of principal coordinates can be successfully used for tracing the exact origin of mussel samples within such a small water area. Canonical analysis of principal coordinates proved superior in the correct classification of the samples.

Automated summary

This study examined the effects of age, sampling location, and sex on the element contents in the soft tissues of Mytilus galloprovincialis. It found that most element contents decreased with age, and there were significant differences in element accumulation patterns among mussels from different sites. Sex did not significantly affect element accumulation. The ratio of soft tissue dry weight to total weight and certain morphometric parameters were strongly correlated with element contents.