Marine litter

Marine litter is a clearly visible problem along the Baltic Sea coastline. It also appears under the surface and in many different size classes. The smallest microlitter is invisible to the human eye, but reaches the marine food web when animals ingest it. Larger marine litter deteriorates habitat quality and can cause direct harm to animals when they swallow it or become entangled. Around 70 % of the marine litter in the Baltic Sea is plastic. Plastic materials are of special concern due to their risks to the environment and slow degradation. The regional goal agreed in HELCOM is to reduce the amount of marine litter significantly by 2025 and prevent harm from litter in the coastal and marine environment.

Besides having effects on the environment, marine litter also has a strong socioeconomic dimension. Marine litter may affect human activities and health, reduce the value of tourism and recreation, or result in direct costs for removal. It can also damage fishing gear, contaminate catches or be a risk to navigational safety.

Marine life is impacted both directly and indirectly. Litter may cause harm to animals when they ingest it, by clogging or injuring their digestive tract, or by causing contamination. Another main impact occurs when animals are entangled and strangled in lost fishing equipment or packaging material. Additionally, marine litter affects the quality of habitats by effects on physical structure or local biogeochemistry, and is a possible vector for the transfer of non-indigenous species, leading to effects on biodiversity. The risk associated with microlitter for marine animals is under extensive study (Werner et al. 2016). Artificial, polymer materials, more commonly known as plastics, are of special concern due to their longevity, which is further prolonged under the photic zone, and because they may be a pathway for harmful chemicals into the food web.

Globally, it is estimated that 275 million metric tons of plastic waste were generated in 2010, calculated for 192 coastal countries, and that between 4.8 and 12.7 million metric tons entered the ocean, and that the world annual plastic production is still increasing (Jambeck et al. 2015). Most plastics are used in packaging or in the building industry and are discarded within a year of their production. In HELCOM, assessment approaches based on core indicators are currently underway for beach litter, litter on the seafloor and microlitter. Threshold values for the assessment are being developed in an EU-process.

Marine litter on the beach

Monitoring of beach litter at Baltic Sea regional scale is under development. Currently available data give an indication of how marine beach litter is distributed along Baltic Sea shorelines, suggesting that the highest densities of beach litter occurs in the Gulf of Finland, Bothnian Sea, and Northern Baltic Proper (Figure 4.3.1). The differences among sub-basins are attributed to actual differences in littering, as well as in the levels of beach cleaning. In addition, the shape of the coastline, winds, and the direction of water currents appear important in determining where litter accumulates.

Figure 4.3.1. Indication of the occurrence of beach litter items in different sub-basins of the Baltic Sea, presented by eight regionally agreed litter material categories (‘Plastics’ denote all types of artificial polymer materials). The monitoring results have been recalculated to represent the number of litter items per hundred metres of beach. The bars show averages for all countries within the same sub-basin based on available data from Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland and Sweden over 2012-2016., However, there is variability with respect to the time period for monitoring and the length of beach monitored in the underlying data. Differences among geographic areas are influenced by the level of local human activities but also by various other factors, such as the shape of coastline, winds and water currents. Source: HELCOM (2018ad).

The monitored sites are categorized into either urban, peri-urban, rural or reference beaches, based on how close they are to human activities. The average number of beach litter items on reference beaches is about 47 per hundred meters of shoreline, and up to about 280 items per hundred metres on urban beaches (HELCOM 2018ad).

Plastics are clearly the most common litter materials (Figure 4.3.2). In much smaller amounts, paper and cardboard are the second most common materials on urban beaches, whereas metal, glass and ceramics are the second most common on the other three types of beaches. Litter items at urban and peri-urban beaches are more likely to originate from activities on land close to the monitored site, whereas beach litter recorded at rural and reference beaches are more likely to come from sources at sea.

Figure 4.3.2. Proportions of beach litter items within each of eight regionally agreed litter material categories. The results are presented separately for beaches classified as either urban, peri-urban, rural or reference beaches, based on estimates of the average number of litter items per 100 metre of shoreline in the Baltic Sea using available data for years 2012- 2016. Source: HELCOM (2018ad).

The most frequently occurring beach litter items at Baltic Sea scale are attributed to eating, drinking or smoking activities, such as food wrappings, bottles or lids, as well as plastic pieces of different sizes (Table 4.3.1). These items are common in all parts of the Baltic Sea, together with items related to industrial packaging, such as sheeting, strapping bands and masking tape (based on data from fifteen sub-basins). Derelict fishing gear are among the twenty most common items in the Eastern Gotland Basin, Gdansk Basin and Kiel Bay. It is noteworthy that balloons or balloon-related items are found among the top ten items in nine of the fifteen sub-basins (HELCOM 2018ad).

Litter on the seafloor

Litter that enters the marine environment can be transported over long distances by water currents, and it often accumulates on the seafloor, far away from its original source. Hence, all types of sources can contribute to seafloor litter. However, items associated with maritime activities are a major component. So called ‘ghost nets’, which are defined as abandoned, lost, or otherwise discarded fishing gear, pose an especially large risk to marine life since they continue fishing, trapping not only fish, but also other marine life including birds and marine mammals over long timeframes. Experiments have shown that the catching efficiency of lost gillnets amounts to approximately 20 % of the initial catch rates after three months, and around 6 % after 27 months (WWF Poland 2011).

Ghost nets are lost fishing gear that continue fishing on the sea floor, catching fish as well as other species. Photo: Wolf Wichmann.

Seafloor litter is monitored in connection to fish trawling surveys, by counting litter caught in the fish trawl. The survey provides an indication of litter on the seafloor, but does not cover shallow water areas or complex substrates, and not all parts of the Baltic Sea. For example, the Gulf of Bothnia is not covered. Items made from natural materials, such as wood, natural fibres and paper, and plastic items dominate in most sub-basins (Figure 4.3.3). The proportion of metal items is highest in the Kiel Bay and the Eastern Gotland Basin.

Slightly over half (58 %) of the 1,599 hauls reported in 2012-2016 contained marine litter items (HELCOM 2018ae). The average number of items was clearly highest in the Western Gotland Basin. Plastic was the most common litter material category at the Baltic Sea scale, constituting on average around 30 % of the number of items and 16% of the weight. A weak but statistically significant increase in seafloor litter representing non-natural materials was seen over the studied time period.

Figure 4.3.3. Proportion of marine litter material categories in bottom trawl hauls for sub-basins covered by the survey. No data for number of items by category was available for the Great Belt. Based on data from the Baltic International Trawl Survey coordinated by ICES, summed for all years 2012-2106. Source: HELCOM (2018ae).

Microlitter

Most of the environmental harm of microlitter has been associated with microplastics, and the potential risks associated with ingestion of microplastics by marine organisms. The composition of microlitter with respect to different materials has not yet been regionally assessed in the Baltic Sea. Based on the composition of other types of litter in the Baltic Sea, it is likely that the majority of microlitter is derived from the breakdown and usage of larger plastic litter items, although other components may also be important (Magnusson et al. 2016, See also Box 4.3.1).

So far, microlitter has only been sampled for a few years in the Baltic Sea and a number of different methods and sampling devices have been used. Coordinated regular monitoring is under development.  As one example of results, 0.3-2.1 particles per cubic metre were noted in the Gulf of Finland (Setälä et al. 2016) and 0.04-0.09 particles per cubic metre were recorded in the South Funen Archipelago, Belt Sea (Tamminga et al. 2018), both studies using Manta trawls with mesh sizes over 333 micrometres.

In comparison to other seas, studies of the abundance of plastic debris near the Swedish city of Stockholm has been estimated to be at similar level as close to urban areas in California, USA, and the overall abundance in the Stockholm Archipelago similar to reports from the north-western Mediterranean Sea (Gewert et al. 2017).

Impacts and recovery

Many types of marine litter degrade very slowly and inputs to the sea accumulate in the environment – in the living environments of organisms or inside of species. In addition, the degradation process will change the nature of the problem, so that litter entering as macro-litter may turn into microlitter over time, and may additionally cause chemical effects.

Political will and robust regulatory action are key factors for reducing the pressure from marine litter. Efforts to change consumption patterns are key to stop litter from entering the marine environment, and are expected to depend strongly on public awareness.  In addition, regulatory frameworks and actions to improve waste and wastewater management are of high significance.

A large number of measures have been agreed on by HELCOM over recent years, which directly or indirectly can be expected to result in reducing amounts of marine litter. The 2013 HELCOM Ministerial Declaration (HELCOM 2013a) contains a commitment to achieve a significant quantitative reduction of marine litter by 2025 (compared to 2015) and to prevent harm to the coastal and marine environment. To achieve this goal the effective and timely implementation of land-based, sea-based and educational and outreach actions as defined in the HELCOM Action Plan on Marine Litter is needed (HELCOM 2015c).