Adaptation of Mytilus galloprovincialis Lmk. to chronically polluted environments and its ecological implications

Supervisors: Manu Soto (UPV/EHU), Mikel Becerro (CSIC)
Adaptation to local environments plays an important role in biomarker interpretation in the mussel (Mytilus galloprovincialis). Particularly important for ecosystem health assesment and biomonitoring studies, adaptative responses to persistent chronical pollution is of major concern in modern biomarkering studies. The research thesis herein aims to compare adaptive responses of mussels to the chronically polluted eutrophic location of Arriluze versus Plentzia, the reference site. Both sites differ upon a variety of ecological settings that are crucial to study population adaptation. Histological analysis showed that the mussels from Arriluze and Plentzia showed a good health status that as to March 2014, and were ripe and ready to spawn. However, individuals from Arriluze had greater Flesh Condition Index (FCI) than those from Plentzia. Induced spawning provoked a decline of FCI in mussels from both locations, but its extent was great variable, which was confirmed by histological analysis. Reproductive strategies play a role in understanding lipophilic contaminant mobilization and handling within mussels, suggesting that continuous spawning can be a method to decline PAH body burden in female mussels from Arriluze. Also, shells from Arriluze and Plentzia have a different morphology, indicating that mussels from Arriluze are higher for a given length, whilst individuals from Plentzia are consistently wider. Both trends were more evident in larger mussels. Shell surfaces from Arriluze showed a greater extent of abnormalities than those from Plentzia. Growth ring analysis suggested that mussels from Plentzia were consistently older than those from Arriluze for any given length, as a result of enhanced food availability that may unbalance detoxification costs. Despite there is a trend towards producing heavier and thicker shells in mussels from Arriluze, there is ultrastructural (SEM) evidence to assert that aragonitic calcification is weaker in Arriluze than Plentzia. Comparative calcification impairment is explained partially by environmental factors (e.g. salinity) and different life strategies of mussels from both sites. These results were confirmed by greater predation susceptibility in Arriluze, suggesting as well that Carcinus maenas predation might be an structuring factor in mussel populations from Arriluze. Finally, the present research work is alligned with previous studies that suggest that evolution of Mytilus galloprovincialis rapid and plastic, which allows it to be a widespread, ubiquitous, invasive species.