The effects of microplastic and natural particles on the invasive mussel Mytilus galloprovincialis (Lamarck, 1819) and the native Choromytilus meridionalis

Germishuizen, Matthew

The effects of microplastic and natural particles on the invasive mussel Mytilus galloprovincialis (Lamarck, 1819) and the native Choromytilus meridionalis

Master Thesis

2021

Abstract

Mussels living in coastal environments are often exposed to natural inorganic particles and hence may be well adapted to dealing with high sediment loads. The mechanisms by which they deal with particle loads do, however, cause stress and alter metabolic processes. An increasingly common anthropogenic addition to particle loads in the ocean are microplastic particles. Numerous recent experiments have addressed the impacts of microplastics on metabolic performance, but few of these have used natural reference particles to control for the concurrent effects of particle load itself. This study aims to compare the effects of microplastic and of natural particle exposure on the mussel Mytilus galloprovincialis, an invasive species which has become the dominant mussel in the mid- to low-shore of the south and west coasts of South Africa, but is absent from areas prone to sand inundation. These effects will be compared to those on the native mussel Choromytilus meridionalis, which resides on the low shore, and unlike M. galloprovincialis often occurs in areas prone to sand inundation. Respiration rates, byssus production, clearance rate, body condition (BCI) and survival of mussels exposed to four concentrations of two particle types, polyvinyl chloride (PVC) and red clay were measured. A significant concentration effect was found in the respiration rates of Mytilus galloprovincialis, while C. meridionalis respiration rates were largely unaffected by both particle type and particle concentration. The byssus numbers of M. galloprovincialis were significantly reduced by microplastic exposure, whilst no particle type effects were found in C. meridionalis. Clearance rates of C. meridionalis, on the other hand, were significantly affected by particle concentration, while no effects were found on M. galloprovincialis. The BCI of C. meridionalis was also found to be affected by particle concentrations, while M. galloprovincialis was unaffected. All C. meridionalisindividualssurvived the experiment, while 29 M. galloprovincialis died. Mortality of M. galloprovincialis exposed to the two particle types was not significantly different, although more mortality was suffered in PVC treatments than in red clay treatments. The results reveal that there was indeed a difference in the response of M. galloprovincialis to the different particle types, and that the two species did exhibit different strategies to both particle type, and concentration. Experimental studies of this nature are imperative in order to disentangle microplastic effects from those of particles in general, and to develop a better understanding of potential impacts of plastic debris on marine ecosystems.

Keywords

Biological Sciences

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