MACROALGAL BIODIVERSITY RESPONSE UNDER A MULTIPLE STRESSOR SCENARIO

Biodiversity-Ecosystem Function experimental stu- dies focusing on marine systems are few and produce contrasting outcomes. Here, we provide experimental proofs on how communities, on a natural gradient of diversity, respond under stressful conditions in inter- tidal habitats. In August 2017 a field experiment was performed in Western Sicily (Italy) in a site charac- terized by tidal pools whose biodiversity structure and composition change as a function of the distance from the low tide mark. The pools closer to the sea are more stable from a thermal and oxic point of view and characterized by high algal biodiversity. Those further from the sea are highly variable with extreme conditions and are poorer in species. We chose 12 pools – homogeneous in size and geometry – and, to know the environmental fluctuations, we measured, for 24 hours at the minute resolution, the oxygen concentration (through an oximeter) and the tem- perature (using thermos-loggers). Then, we carried out a manipulative experiment, follow the same field procedures, to investigate the effects of a climatic event (heat wave) in combination with anthropogenic stress (increased gasoline concentra- tion). We used community metabolism (oxygen consumption, mg/L) as a proxy of functioning. At the end of the treatments, we characterized the bio- diversity contained in each pool by scraping 3 quad- rats 10 x 10 cm and related it to community metabolism. No difference was observed in the metabolism between treated and controlled in high diversity pools; whilst significant differences have been found in low diversity pools for the climatic stressor. Regarding to the chemical stressor, no remarkable difference has been found. Interestingly, these results show that under the action of a disturbance, the functioning – as expressed by oxy- gen consumption – can be altered over time. The richer the community increases the ability to restore the control conditions, while the poorer pools were unable to do so.