In this edition of Lapilli+, we highlight an initiative addressing marine litter in western Greece, focusing on pollution from abandoned marine net-pen farms. When fish farming operations go bankrupt and leave their structures at sea, the resulting debris poses risks to wildlife, ecosystems and maritime activities. Such conduct contributes to a pressing environmental issue, which heavily affects the Mediterranean Sea, where litter densities are comparable to those observed in the five major ocean gyres, according to a 2015 study.

Top Sources of Marine Litter and Their Impact on Marine Life

Marine litter pollution originates from a variety of sources, both sea-based and land-based, each contributing significantly to the problem. Sea-based sources include fisheries and aquaculture activities, shipping and offshore mining. On the other hand, land-based sources include poor waste management practices, industrial outfalls, untreated municipal sewage discharges, tourism and recreational activities.

Marine litter poses a significant and multifaceted threat. Among the key impacts are the entanglement and ingestion of marine litter by wildlife, which can lead to injury or death. Plastics also contribute to bioaccumulation and biomagnification of toxic substances that are either released from plastic items or adsorbed onto plastic particles (editor's note, they can stick to plastic particles). Furthermore, marine litter can cause direct physical damage, such as the abrasion of coral reefs by fishing gear and the smothering of organisms living on or near the seabed, all of which compromise the health of marine ecosystems. In addition, recent studies highlight that plastics can act as threat multipliers, intensifying the effects of other stressors like climate change and they can introduce invasive species that disrupt ecosystems.

From our correspondence with Thomais Vlachogianni, Environmental Chemist and Ecotoxicologist, Senior Policy & Program Officer at the Mediterranean Information Office for Environment, Culture and Sustainable Development (MIO-ECSDE)

In Menidi, a small coastal village along the Ambracian Gulf in Greece, technical diver Pascal van Erp witnessed a grim scene last October. While volunteering for the second chapter of the “Operation Ghost Farms — Reclaiming Waters” project, the founder of the nonprofit organization Ghost Diving was saddened by the sight of a few dead grey herons floating inside a recently abandoned fish farm structure.

On previous occasions, van Erp came across carcasses of sea mammals or birds trapped in these structures. They knew there is fish inside those cages, he explained, but when they go in to catch it, they can’t get out and die.

Some fish farming structures in Menidi, Greece, at the time of the Healthy Seas intervention

Apart from occasionally killing wildlife, abandoned fish farms mostly pose a threat to boat traffic and the marine environment. Their structures made of plastic, styrofoam, ropes and metal degrade over time becoming marine litter. Sunken nets may suffocate the vegetation and animals on the seafloor (but also host new ones). As plastics and styrofoam deteriorate, these materials can be ingested by marine life, leading to injuries or death, and entering the food chain. According to a couple experts I reached out to for this newsletter, the problems posed by ghost fish farms are potentially and likely relevant in all areas that have a long presence of marine net-pen aquaculture. In Greece, according to a survey conducted by Ozon, a local partner of the Healthy Seas Foundation, the Dutch nonprofit coordinating the “Operation Ghost Farms — Reclaiming Waters” project that Pascal van Erp took part in, 150 coastal sites are potentially polluted by fish farming-related waste.

A frame showing the locations where, according to surveys done by Ozon, there may be marine litter from fish farms. This data still needs to be further investigated with additional surveys to determine whether fish farms near these areas are active, inactive and what state they are in.

“It is challenging to determine the full extent of the issue with abandoned fish farms,” wrote Thomais Vlachogianni, senior marine litter researcher at the Mediterranean NGO Federation’s Mediterranean Information Office for Environment, Culture and Sustainable Development, in an email. “As it has not yet been extensively studied or widely reported.”

Healthy Seas leadership first stumbled upon the issue in the summer of 2020 while removing derelict fishing nets from a World War II submarine off the coast of Kefalonia, an island in the Ionian Sea, about 18 miles from mainland Greece. During a short break on nearby Ithaca, locals approached the Dutch foundation team with a tip, recalled Healthy Seas director Veronika Mikos: “If you want to clean up something really big, we've got the fish farm here.”

The removal of a net during one of the cleanups in Ithaca (Cor Kuyvenhoven/Ghost Diving)

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