(MWN / 01-03-10)  The oceanic posidonia could disappear three times faster at the end of the 21st Century if the Mediterranean reaches the temperature projected by the IPCC. This is the conclusion of a study carried out between 2002 and 2007 in the National Park of the Cabrera Archipelago.

Sea warming in the Mediterranean Sea speeds up the decline of the seagrass od Oceanic Posidonia: by one more degree in maximum annual temperature of the sea, its mortality grows 3% every year. One team of CSIC has published this finding after having carried out an investigation between 2002 and 2007 in the in the National Park of the Cabrera Archipelago, a relatively pristine area, free of impacts of human activities.

One of the authors of the study, which has just published in Global Change Biology, the researcher Nuria Marbá of the CSIC, explains: “Warming of the Mediterranean sea does not cause appreciable changes in the appearance of new plants, but a net loss of plants and regression of the meadow. The mortality increases both when the threshold temperature exceeds 28 º C, above which mortality of posidonia shoots up, and when the duration of periods of anomalously warm temperatures increases.”

The researchers measured sea temperature at 17 m depth (where posidonia is) continuously for five years. Each year they registered both mortality and birth of the plant.

The work, carried out in the Instituto Mediterráneo de Estudios Avanzados (mixed center of the CSIC and the University of the Islas Baleares) is based on the results of research projects funded by the Ministry of Environment, the BBVA Foundation and the European Commission.

During the researching period, the annual maximum temperature of water was on 1ºC above on average that the one registered in the 90’s in the same area. Between 2002 and 2007 two heat waves were registered, one in summer in 2003 and other one, less strong, in summer in 2006, where temperatura of sea water exceeded 28.5ºC, two degrees above the maximum in the 90’s. Seagrasses more affected were those deepest, which continued to experience losses in the years following the heat wave.

Existing climate models, according to the emissions scenarios projected by the Intergovernmental Panel on UN Climate Change (IPCC) predict an increase in the Mediterranean Sea temperature of 4º C by the end of the 21st Century.

According to the co-author of the study and also researcher in the CSIC, Carlos Duarte, “the results of this study suggest that, if the Mediterranean Sea increases as predicted by IPCC, the loss rate of oceanic posidonia could triple the current rate by the end of this century. The impact could be even higher if the frequency and magnitude of heat waves during the 21st Century increases.”

THOUSAND-YEAR-OLD GROWTH

Due to its show growing and reproduction, the oceanic posidonia needs centuries or millenniums to develop seagrasses and recolonize areas that have lost their vegetation. A large area of the posidonia meadows in the Mediterranean is affected by local impacts (discharges of organic matter with nitrogen and phosphorus, alterations in the coastline, boat anchors and biological invasions).

For the researcher of the CSIC, “global warming is a new threaten to theses meadows, and must be fought by reducing the local stresses and mitigating climate change, which needs global actions.”

The oceanic posidonia is an endemic plant of the Mediterranean that forms extensive thousand-year-old meadows, between zero and 40 m depth. These protected habitats are sinks of fundamental CO2, project the coastline from erosion and are an important reservoir of biodiversity.