Anthropogenic climate change is already affecting the marine plankton populations present in the western Mediterranean Sea. This is the result of a recent study that warns on the increasing surface ocean temperature lowering primary production, which has negative impacts on plankton communities and marine biodiversity.
The studied records from the 10th century up to the present in the the Balearic and the Alboran seas focus on a model group of marine calcifying zooplankton known as planktic foraminifera. Planktic foraminifera are single celled organisms with a shell made of calcium carbonate commonly found in the sedimentary record. They live in the upper ocean, responding sensitively to climate and environmental changes.
The anthropogenic warming occurs more abruptly in the Mediterranean region compared to the global average, affecting marine plankton communities. Since 1880, atmospheric warming has been greater, accelerating the increase of sea surface temperature. Before anthropogenic carbon dioxide (CO2) emissions led to enhanced ocean warming (prior to 1880, according to records), alterations in planktic foraminifera were mainly driven by natural variability. In contrast, during the past ca. 150 years, unprecedented anthropogenic warming of the western Mediterranean Sea has reduced the planktic foraminiferal stock. At the same time, changes in species composition are indicating that the biological productivity of the western Mediterranean diminished.
The results of the study can be seen as a sign of reduced marine productivity caused by anthropogenic warming. A less productive Mediterranean Sea would affect the food web complexity and fish stocks as well as biodiversity, causing a degradation of ecosystem services in the Mediterranean. Together with overfishing, a reduced marine productivity further threatens the rapidly changing Mediterranean Sea ecosystems and natural resources, highlighting once again the need of protecting this sea, adapting and first of all addressing the mitigation of climate change.
