Seas and oceans cover nearly three quarters of the Earth’s surface. Human interference with the natural environment causes changes in their natural condition and biodiversity. The average surface acidity of seas and oceans has been gradually growing for several decades now (since 1990, the pH of oceans has decreased from 8.10 to 8.06). These changes, caused by factors such as increased CO₂ emissions, negatively affect organisms which live in seas and oceans, especially those whose skeletons are built of calcium carbonate.

In order to maintain and strengthen natural biodiversity in the world, Key Biodiversity Areas (KBAs) have been established under the auspices of the International Union for Conservation of Nature (IUCN). Some of these areas are protected by local legal regulations. From among all the marine areas in the world considered by international organisations of key importance to biodiversity, 46% are nowadays preserved (compared to 37% in 2005). Legal protection extends to the largest degree to key marine areas in Europe (71%), and to the smallest in Western Asia (16%). Since 2005, this indicator has improved most notably in Northern and Sub-Saharan Africa, where the percentage of the protected key marine areas has grown from 22% and 25%, respectively, to 40%.

In Poland, 175 Key Biodiversity Areas with a total area of 61,000 km² have been established, 45 of which are marine areas. Nearly 90% of Poland’s key marine areas are protected by the law. This percentage has grown considerably since Poland joined the EU (in 2003, it was 29%) and when some areas were added to the Natura 2000 programme.

Biodiversity of seas and oceans is threatened by e.g. overfishing, meaning excessive and unregulated exploitation of fisheries. This causes the populations of the fished species to fall below levels allowing their safe restoration. For the purpose of monitoring sizes of fish populations, they are classified into three categories: overfished stocks, fully exploited stocks and non-fully exploited stocks. Only the two latter categories are regarded as biologically sustainable, and there have been increasingly fewer of them in the world: the percentage of fish stock at biologically sustainable level has decreased from over 70% in 2004-2006 to the current 66%.

Average proportion of Marine Key Biodiversity Areas (KBAs) covered by protected areas (%)

In 1992, during the Earth Summit in Rio de Janeiro, a Convention on Biological Diversity (or the Rio Convention) was drafted and subsequently signed by 196 countries. Following its provisions, the EU established a European Ecological Network Natura 2000, whose aim is to preserve natural habitats and valuable or threatened species. The network is based on two directives: the Birds Directive (on the conservation of wild birds) and the Habitats Directive (on the conservation of natural habitats and of wild fauna and flora). The Natura 2000 network extends over 573,000 km² of marine areas in the EU, of which 7,000 km² are situated within the Polish territories.

Coverage of protected areas in relation to marine areas (Exclusive Economic Zones)^a (%)

a Exclusive Economic Zone is an area established by international agreements, where the coastal state has the exclusive sovereign right to scientific research, exploitation of natural resources, construction of installations and structures, as well as the protection and preservation of the marine environment.