Taking the acid test: Mediterranean limpets face up to climate change

Impacts of climate change involve the interactions of multiple stressors on intertidal organisms, but rarely are the impacts of these stressors examined together. Many tests are also conducted in artificial, controlled laboratory conditions, without making use of natural opportunities to test performance of organisms under different environmental stressors. Given its small tidal range, the Mediterranean Sea provides such an opportunity, with a very fine scale environmental gradient and species living very close to each other over the tidal gradient. The vertical distribution of the limpets, Patella rustica and P. caerulea overlap in Palermo, Sicily, but despite this they have different thermal windows. The higher shore P. rustica had a lower metabolic rate than the mid shore P. caerulea, and was also more tolerant of thermal stress, being able to maintain heart function up to 38°C as opposed to 36°C in P. caerulea. When heat stressed, P. rustica also induced heat shock protein expression, whereas expression in P. caerulea was very low. Utilizing a natural gradient of seawater pH (caused by CO2 vents off Vulcano Island, Sicily), the combined effects of ocean acidification and thermal stress were investigated, which revealed an intraspecific gradient in species response. In general both species were more tolerant of thermal stress, maintaining heart rates between 41- 43°C, but individuals stressed by lower pH were less tolerant as compared to those further from the vent which experienced natural seawater pH. Heat shock protein expression and function of metabolic enzymes were also analyzed. These preliminary findings highlight the need for testing the impacts of multiple stressors, but also the benefits of utilizing naturally occurring habitats to investigate the interactions between environmental stressors.