Effects of climate change on the Mediterranean

Global change and microplankton

Microplankton diversity

Plankton is a collective term for all organisms living in the water column that lack their own means of active movement or whose range of movements are more or less negligible in comparison to the movement of the water mass as a whole. Plankton organisms can range in size from a few metres for large jellyfish and salp colonies to less than a micrometre for bacteria. Within the MarPLAN project the biodiversity of eukaryotic marine single-celled plankton organisms was studied in order to answer the question “In what ways can global change affect microplankton?”

To understand plankton distribution and changes therein, we first need to know how diverse it is. Diversity can be hidden within an easily identifiable morphologically defined species. Although this species may be considered cosmopolitan, it can possibly be divided into several separate species each with a different distribution patters. For example, MarPLAN discovered that the cosmopolitan species Fibrocapsa japonica in fact consists of two different species. The second one was discovered in the Adriatic Sea.

Phytoplankton

In the temperate zones, many phytoplankton species form blooms during restricted periods of the year. Global warming caused some species to bloom earlier in certain places, and to shift the distribution of these blooms tends towards the poles. New species may appear in regions, partly through introduction (for example, via ballast water dumping) and partly through polewards range expansion of warm-water species.

Several MarPLAN research partners collaborated to assess these trends in the dinoflagellate genus Ceratium. Over the last century, several species of the genus Ceratium have disappeared from study sites in Villefranche sur Mer and Naples, or have become far less common, while new dinoflagellate species have recently appeared.