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 cryptic species. The second one was discovered in the Adriatic Sea. Another research project carried out by CNRSDIMAR (MarBEF partner) focused on the diatom genus Skeletonema. In this genus, several new species were discovered and a biogeographic study showed that some of the newly discovered species had a restricted distribution pattern. For instance, Skeletonema gretae is found only along the Atlantic coasts of the US

In the temperate zones, many phytoplankton species form blooms during restricted periods of the year. Under influence of global warming, some species show a propensity to bloom earlier in some places. In addition, the distribution of these blooms tends to shift polewards. New species may appear in regions, partly through 38 introduction (for example, via ballast water dumping) and partly through polewards range expansion of warm-water species. Several MarPLAN research partners collaborated on assessing these trends in the dinoflagellate genus Ceratium (Fig. 4).