Exploring dreissenid mussels in Amsterdam

Investigating their presence and swimmer's perception

Despite the absence of official swimming locations in Amsterdam due to inadequate water quality, many people still enjoy swimming in its waters. Dreissenid mussels, prevalent in Amsterdam, can filter algae and organic matter, improving (swim)water quality. This thesis explores two popular swimming areas, Marineterrein and Sloterstrand, where an artificial reef and a mussel screen have been installed to enhance the aquatic environment. This research investigated how these structures can attract dreissenids to improve water quality and examines what the perceptions of water quality are of swimmers and if mussels can help people connect with the aquatic environment. A mixed-method approach was used: a habitat suitability index (HSI) assessed the suitability of these sites for dreissenids, and onsite observations were conducted through snorkelling and using an underwater drone. Additionally, 18 semi-structured interviews were performed to understand swimmers' perception and affinity/ relationship with the water. According to the HSI, Sloterstrand is very suitable to attract dreissenids and Marineterrein is marginally suitable. However, no mussels were found on the structure at Marineterrein, though they were present on the quay walls. At Sloterstrand, dreissenids were located on the screen, but more were found on the quay walls as well, indicating that substrate type could influence mussel colonization. However, more research is needed on a longer time frame to identify colonization influences better. The varied perceptions of water quality underscore the need for better public awareness and education. While sensory observations and local knowledge play roles in these perceptions, understanding water quality issues still needs improvement. Almost no one was aware of the human-made structures introduced at the sites, and nearly half of the interviewees were aware of mussels' role in filtering water. Therefore, raising awareness about the environmental benefits of mussels and nature conservation can foster a more holistic approach to interactions with aquatic environments, though the actual behavioral impact remains uncertain.