Biodiversity describes the variety of life on earth, and it operates from genes and species to entire ecosystems. Biodiversity therefore refers to all life-forms and their behaviours, the environments in which they live, and the complex system of relationships between organisms, such as food webs and competition for resources.

Non-indigenous species are species introduced outside their natural range, which might survive and subsequently reproduce and therefore threaten biodiversity. These species are introduced in situations where exchange of people or goods takes place between countries and continents, by shipping for example.

Commercially exploited fish and shellfish are all living marine resources targeted for economic profit such as the bony fish, sharks, crustacean, molluscs, jellyfish and starfish. Those stocks should be in a healthy state and exploitation should be sustainable.

Food webs are networks of feeding interactions between consumers and their food. This feature addresses the rates of circulation of matter and energy transfer within the system and levels of productivity in key components, and ecosystem structure.

Fishing is the most influential factor in the size of fish stocks, with a direct impact on the entire food web. Harvesting large fish increases their mortality rate. This means that, without natural enemies in the marine environment, there is an increase in the population of smaller fish, which are usually the victims of large fish. In turn, catching small fish such as herring is reducing the food supply of marine mammals.

Chemical pollution of the marine environment is another factor that affects food chains. Chemicals accumulate in marine organisms and travel down the food chain, eventually accumulating in large fish and marine mammals.

Eutrophication is a process driven by the enrichment of water by nutrients, especially compounds of nitrogen and phosphorus, leading to increased growth, production and biomass of algae, changes in the balance of ecosystem and water quality degradation.

The main nitrogen load comes from agricultural areas, nitrogen gases, aquaculture, industrial water and adjacent oceans. The main contribution of phosphate comes from domestic and industrial sewage and waste water.

The sea-floor integrity reflects the physical, chemical and biological characteristics of the sea bottom. These characteristics delineate the structure and functioning of marine ecosystems, especially for species and communities living on the sea floor. 

Hydrographical conditions are characterized by the physical parameters of seawater: temperature, salinity, depth, currents, waves, turbulence, turbidity. They can be altered by human activities, especially in coastal areas.

“substances (i.e. chemical elements and compounds) or groups of substances that are toxic, persistent and liable to bio-accumulate and other substances or groups of substances which give rise to an equivalent level of concern” (Water Framework Directive, Article 2(29)).

Examples of such substances found in the marine environment include pesticides, pharmaceuticals and heavy metals, among others.

Substances accumulating in an organism are likely to be transferred in the food chain. Biomagnification is a process where the concentration of a contaminant increases within the food chain.

Marine litter is a global concern, affecting all the seas and oceans of the world. Every year, millions of tons of litter end up in the reservoirs worldwide, turning it into the world’s biggest landfill and thus posing environmental, economic, health and aesthetic problems.

The sources of underwater noise are all mechanical devices operating in the sea such as ships, sonar, dredgers, excavators sand, cables, causing the electromagnetic radiation, cooling water systems, military action. Sounds may propagate in the water in it at much greater distances than in air.