The marine ecosystem plays a vital role in regulating the climate system, yet it is also highly vulnerable to the effects of climate change, both in terms of its composition and structure and its behaviour. A number of changes have been observed in the seas that bathe the Spanish coasts. These include the surface and intermediate water temperature of the sea, as well as its salinity and acidity; alterations in primary production; the appearance of sub-tropical and tropical marine species that may prove harmful for the existing biodiversity; and the occasional proliferation of toxic microorganisms, etc.  All these changes are attributable to the global warming that has occurred in recent decades.
 
The fishing sector is directly affected by the negative impact of climate change on the marine system and may occasionally benefit from the appearance of commercially feasible fish stocks in areas where they did not previously exist, brought about by climate change.