Abstract
The Mediterranean Sea is a hotspot of plastic pollution, posing risks for marine life with potential economic and ecological consequences. This dissertation focuses on investigating the threats of plastic pollution on the ecosystem of the Mediterranean Sea with the development and implementation of mathematical models that can be used to estimate the ecological impacts of plastic pollution. A validated plastic dispersion model was used to predict concentrations and origins of micro- and macro-plastics in Marine Protected Areas (MPAs). Bioenergetics models were developed to estimate the physiological effects of plastic pollution on specific species of commercial and ecological interest, such as farmed mussels and the threatened Mediterranean swordfish. A Dynamic Energy Budget (DEB) model was used to investigate the physiological effects of microplastics on the mussel Mytilus galloprovincialis. To support the DEB model a laboratory experiment was conducted with 5 different conditions of ...
The Mediterranean Sea is a hotspot of plastic pollution, posing risks for marine life with potential economic and ecological consequences. This dissertation focuses on investigating the threats of plastic pollution on the ecosystem of the Mediterranean Sea with the development and implementation of mathematical models that can be used to estimate the ecological impacts of plastic pollution. A validated plastic dispersion model was used to predict concentrations and origins of micro- and macro-plastics in Marine Protected Areas (MPAs). Bioenergetics models were developed to estimate the physiological effects of plastic pollution on specific species of commercial and ecological interest, such as farmed mussels and the threatened Mediterranean swordfish. A Dynamic Energy Budget (DEB) model was used to investigate the physiological effects of microplastics on the mussel Mytilus galloprovincialis. To support the DEB model a laboratory experiment was conducted with 5 different conditions of microplastics and suspended sediment (8 mussels per condition) at which the mussels’ clearance rate was measured. A Wisconsin-type bioenergetics model was developed for the Mediterranean swordfish Xiphias gladius and evaluated with fisheries observations data. The plastic distribution model predicted that the coastal zone is more impacted than open waters, with both micro- and macro-plastics occurring in higher concentrations near the coast. Thus, aquaculture locations and protected areas such as Natura 2000 sites and national MPAs, which are commonly restricted near the coastline, accumulated more plastics than Cetacean Critical Habitats (CCHs), which are usually larger and extend to the less impacted open waters. The model also predicted that the size of plastic litters plays a key role in their dispersion and ultimate destination, with transboundary pollution being important, especially for macroplastics, as most of the studied Mediterranean countries (13 out of 15) had at least one national MPA with over 55% of macroplastics originating from sources beyond their borders.The impacts of microplastics on farmed mussels were assessed in 30 locations across the basin. The DEB model was calibrated and validated with literature growth and clearance rate data as well as with the data extracted from the conducted experiment. The model showed that, on average, the clearance rate of farmed mussels was reduced by 0.8-4.5%, leading to minor implications on growth and reproduction. However, in at least one location, the effects of microplastics were considered important, with an estimated 8-22% reduction in clearance rate and corresponding reductions in dry tissue and egg production.The Wisconsin type swordfish bioenergetics model simulated daily prey consumption and growth was validated against fisheries observational data, showing reasonable agreement, while the estimated annual egg production per individual was similar to those stemming from stock assessment datasets. The model suggested that each individual is reproductively active for approximately 15 days, while the commonly reported spawning season of the whole population lasts approximately 90 days. Future work could focus to simulate prey distribution and horizontal migration to enable the investigation of physiological impacts of plastic pollution on the Mediterranean swordfish. Yet, the developed model, is a significant step forward as it is the first bioenergetics model for this threatened species.Overall, the mathematical models developed, validated and implemented in the dissertation provide insights into the impacts of plastic pollution on the Mediterranean ecosystem and can support policy decisions to reduce plastic pollution and protect marine life.
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