MESOCOSM EXPERIMENT OF INCREASING TEMPERATURE AND EFFECTS ON THE PLANKTON COMMUNITY OF A MEDITERRANEAN LAGOON

Water temperature is expected to increase in coming decades as a result of global warming and predicting the consequent responses of organisms is a complex challenge. In this work the effects of increase in temperature on the plankton community were investigated. Specifically, two hypotheses were tested: (1) warming increases metabolism of the system and drives it towards a small-species dominated system (bacteria-based foodweb), (2) warming benefits harmful algal species. A 16-days indoor mesocosm experiment was performed in February 2015 incubating water from Cabras Lagoon (Sardinia, Italy). Three treatments were applied in triplicate mesocosms: at 11 °C, i.e. present-day winter mean water temperature, based on long-term data from the lagoon, at 14 °C, i.e. predicted winter temperature in the region after 100 years, and at 17 °C, i.e. predicted winter temperature after 200 years. Preliminary results show a temporal increase in abundance of smaller phytoplankton species outcompeting the larger ones, and a simultaneous disappearance of flagellates in all the treatments. Regarding HAS, Aphanizomenon gracile and Pseudanabaena catenata (potential producers of saxitoxin and anatoxin, respectively) were observed in all the treatments.