Impacts caused by marine litter on marine ecosystems.

It is recognized that the anthropogenic litter and in particular the plastics affect ecosystems and marine organisms.

Marine litter can cause impacts in many ways, namely, imprisonment and/or ingestion of debris and fragments by organisms, as vehicle facilitator of the transport of invasive species, as an element available for a new habitat for colonization.

The impacts depend on the type and size of marine litter and on the organisms.

The frequency of impacts is conditioned by the type of litter. As much as it was possible to establish up to now, 80% of the impacts are associated with the plastic litter while the paper, glass and metal contribute less than 2%.

Approximately 20% of the total litter categories represent a high risk to the imprisonment. Many of these materials are related with the activity of fishing, such as fishing net, traps and ropes, however other materials, such as bags and strips of plastic, textile fibres, etc. can also cause incidents by imprisonment.

The phenomenon of the ingestion of plastic litter intentional or accidental is already well documented and occurs in all types of wildlife including in larval state.

The ingestion of plastic is more prominent in populated areas and polluted, but there are reports from all over the world.

The ingestion of plastics can also act as a facilitator of vehicle transport of chemicals for the organisms. Some plastics contain potentially harmful chemicals that are incorporated during the manufacturing process. These additives which include the plasticisers, antimicrobial agents and flame retardants may be released to the body when ingested. It is also known that the additives for plastics adsorb the persistent organic pollutants (POPs) of water and that in a few days the concentration at the surface of the plastic can increase some orders of magnitude compared with the levels in the surrounding water. If these chemicals adsorbed are released during the ingestion this is an easy way of transferring chemicals to the biota.

It is also known that the marine organisms use in many cases the litter as habitats for hiding, fix and move to new territories. This type of dispersion is not recent since it is known that branches/tree trunks, ash and floating fruits are means of promoting colonization millions of years ago. This, however, has become a serious problem, thanks to the recent proliferation of floating materials, especially plastics. This transport is done passively, without control over the species, materials and models of transport other than hydrodynamics or environmental factors.

An example of this is the billions of plastic microparticles (particles of varying sizes between 300 µm and 5 mm) that float by oceans and which are potential carriers of invasive species (non-native and dangerous). The advantage of the plastic material as a transport mechanism it is its longevity in the sea and its surface properties that favour the fixation and therefore the possibility of transport to new locations. As a result, this type of species (rafted species) can alter the composition of ecosystems because they can compete with other species, carry diseases and alter the genetic diversity through the intersection with local species. This phenomenon is spread across all waters and the surrounding ocean areas on all continents.

The presence of marine litter can cause changes/modifications in the community structure of species by modifying the original habitat, introducing pollutants or new species and invasive, changing the level of the climax of the community.

Evidence of these effects come mainly from studies localized but not yet evaluated its real dimension on a larger scale. The greatest evidence of harm is reflected in measurable changes in communities or decline of populations or species as a direct consequence of the ingestion of plastics. However, evidence of changes in populations or species is almost impossible to obtain because the number of human and natural factors that interact to determine the survival and reproductive success of each animal is very large.