Effects of warming on a Mediterranean phytoplankton community

Predicting the responses of organisms is a complex challenge especially when water temperature is expected to increase over the coming decades, as a result of global warming. In this work the effects of warming on phytoplankton communities were investigated. An indoor experiment was performed, where water from a Mediterranean lagoon was incubated at different temperatures. Three treatments were applied in triplicate incu- bation units: the control (11 ◦C), 3 ◦C increase (14 ◦C), and 6 ◦C increase (17 ◦C). Our results showed significant effects by warming on phytoplankton. The abundance of relatively smaller taxa (Chlorella sp. and Planktothrix agardhii–rubescens group) increased at 17◦C, whereas the abundance of relatively larger species (Cyclotella sp. and ThalassosiraCE1 sp.) decreased, compared with the control. This shift towards smaller taxa resulted in a higher total biomass but lower chlorophyll a concentrations at the highest temperature.