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Other impacts


Waste

Northern gannet with rests of a fishery net as nesting material. Photo: H. Glader (NABU)
Northern gannet with rests of a fishery net as nesting material. Photo: H. Glader (NABU)
Dead seabird, entangled in a net. Photo: J. Baer (NABU)
Dead seabird, entangled in a net. Photo: J. Baer (NABU)

Despite international agreements (such as the 1973 MARPOL Convention), many million tonnes of plastic still enter the oceans each year, including significant quantities in the North Sea and the Baltic Sea. Offshore industries, research, oil and gas platforms and aquaculture further add to marine contamination with waste. In many cases, the consequences for marine life are devastating. Birds especially mistake plastic for food and sometimes even feed it to their young. Once their stomachs are engorged with indigestible plastic, birds starve or die of internal organ damage. Many suffocate or are strangled by large pieces of waste. Marine mammals are mainly threatened by dangerous ghost nets, remnants of fishing boats or trawlers which drift virtually invisible and forgotten in the sea and in which cetaceans and dolphins, fish and many other sea creatures become entangled and perish.

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Pollutants

The main pathway by which pollution enters the sea is directly from land via rivers and the atmosphere, although large quantities of pollution are also discharged by offshore facilities, aquaculture and ships. It is not just the volume and diversity of pollutants that represent a hazard to the marine environment. In many cases, pollution harms marine organisms through gradual processes such as the accumulation of substances in the food chain. Heavy metals such as mercury cause genetic defects in organisms that can lead to deformities. Both heavy metals and pesticides bio-accumulate across the entire food chain. This is a threat most of all to marine mammals such as harbour porpoises and grey seals.

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Marine energy

The movement of water in the seas offers huge potential for generating energy. Unlocking this potential on a large scale takes major engineering effort, often with adverse impacts on valuable marine ecosystems. Besides advanced engineering, efficient energy generation from the seas also requires sufficiently fast-flowing water. This limits the choice of sites for marine energy installations to specific marine and coastal areas, many of which are ecologically valuable. The impacts of the technology depend on the generation method. Tidal power systems, for example, can be a barrier to fish migration, marine current systems cause underwater noise or alter current patterns and so affect the drift of planktonic larvae, while some wave energy generators need very large foundations that can destroy benthic organisms.

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Climate change and acidification

The North Sea and the Baltic Sea are relatively shallow, and this makes them two of the fastest-warming seas on the planet. Rising water temperatures both attract temperate species not indigenous to our waters and displace hitherto indigenous cold-water species to colder seas further north. As well as the rise in water temperatures, the increasing carbon dioxide levels associated with climate change also harm marine ecosystems in ways that can already be verified today. Atmospheric carbon dioxide is absorbed by the sea, where it forms carbonic acid. When this breaks down, the pH value of the seawater changes – the water becomes more acidic. This acidification poses a serious problem especially for calcifying organisms such as mussels, sea urchins and also diatoms because it prevents them from forming their shells from calcium carbonate as they need to in order to live.

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Nutrients

The North Sea and Baltic Sea continue to suffer from excessive nutrient pollution, which places severe pressure on the marine environment and threatens biodiversity. While North Sea and Baltic Sea nutrient concentrations have been seen to decrease since the 1980s, nutrient pollution in our seas still causes severe changes in ecosystems. Excessive nutrient input clouds the water, meaning that light can only penetrate to a lesser depth. As a result, seagrass meadows and kelp forests, once found up to 30 m down in the North Sea and Baltic Sea, can no longer thrive at such depths today. This loss also negatively affects fauna species that depend on such vegetation.

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Geo-engineering

Geo-engineering is a common term for large-scale intervention in ecosystems with the aim of halting climate change. Some such strategies target the oceans, as with the widespread ‘fertilisation’ of ocean regions with iron to stimulate phytoplankton blooms and thus sequestrate climate-damaging carbon dioxide. The impacts of these techniques on affected ecosystems are still largely unexplored, but they are likely to be similar to the eutrophication of the seas by increased nutrient levels. Not all consequences of such large-scale intervention in biochemical processes are predictable, however, and the use of geo-engineering techniques could have effects on marine life in an extent that today is hard to conceive.

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Carbon sequestration

The oceans are Earth’s largest and most important carbon sinks. There are plans to make use of this by turning the seas into permanent stores for ‘excess’ carbon dioxide, thus preventing its harmful effects on the climate and slowing down the greenhouse effect. Injecting carbon dioxide into the water column is banned under the London Protocol and the OSPAR Convention, but sequestering it at great depths in sub-seabed formations is allowed. The use of such techniques can be assumed to involve major risks. If large quantities of carbon dioxide were to escape, serious consequences to the marine environment such as pH changes and harm to key microbial deep sea communities would be inevitable. Injecting carbon dioxide can also cause the release of other pollutants already present in the sea floor.

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