Samenvatting

Information about the sources of plastic litter found in the Zeeuwse Delta is still scarce. This problem is addressed by this study with the aim to identify the possible sources of plastics that washed ashore on a selection of beaches in the Zeeuwse Delta. For this study the source and origin of the plastics is tried to be identified with the use of biofouling organisms that are attached to the beached plastic litter. In order to identify the sources based on biofouling, plastic containing biofouling was collected on the selected beaches of Vlissingen-Dishoek, Oostkapelle, Neeltje Jans and Kwade Hoek. Important parameters studied during this project were: type of species that is found as biofouling and where they originate from, type of plastic the biofouling is found on and age of the plastic based on state of degradation and percentage of coverage of the fouling organism. The result were presented in
graphs and discussed based on the stated parameters and compared to the results of earlier done project by Wageningen University & Research. The main results of this study were that all identified fouling organisms were native to the North Sea, with only the A. modestus found as invasive species, which has been found in the North Sea since World War II. The same amount of hard and soft plastics were found with higher numbers of bryozoans on soft plastics, while barnacles were more abundant on hard plastics. Most of the plastics had a high degradation state indicating that the plastics were in the marine environment for a longer period. However most of the plastic were covered for 0-20% by fouling organisms. Based on the larval and metamorphosis stage it was found that the plastic litter had to be in the marine environment for at least a couple of months before biofouling could be
observed. It was not possible to indicate the exact time since different conditions like temperature and wave/current action influence the rate of degradation of the plastic and the growth probabilities of the fouling organisms. The study concluded that since the identified fouling organisms were native to the North Sea and most plastic were presumably only in the water for a couple of months, the plastic originate from sources around the North Sea and close to the Zeeuwse Delta. Further studies to the metamorphosis and growth rates of the fouling organisms can be useful to get an exact indication for how long the fouling organisms has been on the plastic litter.