Abstract
The Manila clam (Ruditapes philippinarum), an invasive species in Northern Europe, can be used as a bioindicator of metal pollution. Seasonal effects on metallothionein (MT) production have not been considered in this species at the northernmost extent of its European distribution. This study assesses the annual seasonal effects on MT and metal concentrations in R. philippinarum from Poole Harbour, UK. R. philippinarum were collected in winter, spring, summer, and autumn throughout 2015, and MT and metal concentrations, as well as biotic and abiotic variables, were quantified. During winter, linear regression analysis showed significant positive relationships between tissue metal and MT concentrations. However, during spring and summer, these relationships were mostly insignificant. MT concentrations during spring had significant positive relationships with tissue and whole weight. Significant positive relationships were also observed between MT and condition index, during summer. During spring and summer, biotic factors seem to override the role of MT as a detoxification mechanism for metal exposure in this species. This is probably due to an increase in MT concentration in spring caused by gametogenesis, associated with increased tissue weight as the gonads expand. A depletion of energy resources, or physical stressors such as heat, may be attributed to the reduced MT production in clams of poor body condition in summer. The evidence from this study suggests that MT may only be a useful biomarker of metal pollution during winter in R. philippinarum in the UK. This verifies the natural variability of MT in this species at high latitudes, and highlights the potential and limits to a widely available bioindicator of metal pollution.
Highlights
Estuarine environments are often subjected to metal pollution, posing a potentially significant environmental concern
In order for MT to present a useful tool in biomonitoring and relay the biological impact of metals to R. philippinarum, external seasonal influences to MT concentration must be constrained
It is shown that gametogenesis and the associated increase in MT concentrations, and condition index, override the effect on MT concentration by metal exposure
Summary
Estuarine environments are often subjected to metal pollution, posing a potentially significant environmental concern. Bivalves, offer their use as bioindicator species due to the accumulation of metals, which may reflect concentrations present in the environment. This can be accompanied by the use of biomarkers, such as metallothionein (MT). MTs are non-enzymatic proteins, consisting of thiol groups (sulphur-hydrogen) that bind to metals, preventing oxidative stress to the organism (Amiard et al, 2006). MT is commonly included in biomonitoring studies and monitoring programmes, such as the Biological Effects and Quality Assurance in Monitoring Programmes (BEQUALM) (Amiard et al, 2006), and in the Natural England suite of assays (Galloway et al, 2008)
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