Tropicalisation and deborealisation of European marine communities

The challenge

Ocean warming is causing a redistribution of marine biodiversity in European seas. It was necessary to understand how marine communities are changing and what this means for food webs and fishery resources.

The solution

AZTI led an international study based on time series spanning up to four decades, drawn from 65 monitoring programmes, with data on 1,817 species. It analysed communities of zooplankton, benthos, pelagic and demersal invertebrates, and fish in the north-east Atlantic, the Mediterranean and the Baltic.

The results

• Over the last 40 years, the north-east Atlantic has undergone a tropicalisation of its communities, with an increase in species typical of warmer waters.
• The Mediterranean and the Baltic have seen a marked decline in organisms characteristic of cold waters, a process known as deborealisation.
• These changes can alter food webs, change the availability of fishery resources and affect species of ecological and commercial interest, such as the European sardine in the Mediterranean or cod in the Baltic.
• The results reinforce the need to maintain long-term observation programmes and to adapt marine and fisheries management to communities whose composition, abundance and distribution are changing as a result of global warming.

*Photo credit: peterwirtz2004@yahoo.com