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In recent years, special wash-down areas have been built in marinas to reduce the environmental problems caused by boat bottom paints. An analysis of Hinsholmskilen by the University of Gothenburg shows that the levels of metals in the seabed were highest closest to the wash-down areas, but also that two invasive amoebas have moved in.

There are about 860,000 recreational boats in Sweden, one of the highest numbers in the world relative to the country's population. However, coastal marinas pose several environmental problems, including high levels of pollutants in both bottom sediments and stagnant water, noise, exhaust fumes and invasive species.

Researchers at the University of Gothenburg have conducted a detailed study of the environmental status of Hinsholmskilen, a major marina in Gothenburg. This was done by sampling the bottom sediments at many locations in the harbor during November 2019. The results are in the Journal of Micropalaeontology.

Higher levels near wash-down areas

"We have analyzed sediments from the seabed in the marina for arsenic and metals such as copper, cadmium, zinc, lead, cobalt, nickel, chromium and mercury. The results show that the levels of these environmentally hazardous substances were higher in the inner part of the harbor and the highest levels were closest to the places on land where the boats can be washed off with a high-pressure cleaner," says Irina Polovodova Asteman, marine geologist at the University of Gothenburg.

Despite the results, the researchers say that the wash-down stations are a good idea, but that in some cases the treatment of the wastewater needs to be improved, so that heavy metals do not flow into the harbor. Furthermore, the researchers found high levels of copper and mercury throughout the marina, reflecting the long-term use of both metals in boat bottom paints.

Amoeba stores phosphorus

When the sediment samples were taken out of the marina, a general survey of the small animals that live in the seabed, the so-called meiofauna, was also carried out. There are large numbers of shell-shaped amoebae, known as foraminifera, which are smaller than 1 millimeter. In Hinsholmskilen there were also many amoebae in the seabed, including two alien species.

"There are two invasive species originating in Asia: Trochammina hadai and Ammonia confertitesta. The former is rapidly reproducing, colonizing new areas and, in some parts of the world, has already outcompeted other species. Ammonia confertitesta is interesting because it has a high capacity to store phosphorus in its cells and could thus counteract coastal eutrophication," says Polovodova Asteman.

Both species are likely to have arrived with ballast water first in Gothenburg harbor and then been carried by the muddy anchors of recreational boats into smaller harbors.