The sea and its biodiversity have been impacted adversely. It is not only the loss of biodiversity due to the decrease in the density and distribution of many original native species, but also the increase in non-indigenous species. The nature and scale of the human interventions at sea and on the land – with effects on the sea - have had a major impact on the marine environment, in particularly since last decades.
The result is a very large decline in the abundance of most fish species. Even locally – in the Belgian part of the North Sea – a number of species that previously were rather common, such as the bottle nose dolphin, the stingray and the flat oyster, have since disappeared. The stocks of commercial species such as Atlantic cod, sole and plaice too have dramatically declined during the last decades.
The causes are very diverse. The fishery pressure is a very significant problem due to overfishing and the impact on the seabed. The quality of the sea water too has changed during the last decades as a result of pollution and eutrophication. Climate change has an effect on the temperature of the water and indirectly affects the distribution of several species as these move up northwards. Besides, the acoustic environment of the water changes due to the noise pollution during the construction of wind farms, shipping, sand mining, defense activities, leisure...
Loss of biodiversity is a problem because the amount of ecosystem services are being reduced or because the marine ecosystem becomes more unstable as the number of species disappear; the pressures on the ecosystem may then become less buffered.
The North Sea is and will remain an area where people are active. It is therefore necessary to protect the biodiversity and to restore it wherever needed in order to find a good and sustainable balance between the natural resources and the human activities on sea. The Marine Strategy Framework Directive, the Habitats Directive and the Birds Directive are important instruments for the purpose. Besides, one must keep working towards a better integration of environmental policy in other policy sectors (fisheries, agriculture, transport, energy...).