Spring distribution of shelled pteropods across the Mediterranean Sea

Abstract. Shelled pteropods represent an excellent sentinel for indicating exposure to ocean acidification (OA). Here, for the first time, we characterise spring pteropod distribution throughout the Mediterranean Sea, a region that has been identified as a climate change hot-spot. The presence of a west–east natural biogeochemical gradient makes this region a natural laboratory to investigate how the variability in environmental parameters may affect pteropod distribution. Results show that pteropod abundance is significantly higher in the eastern Mediterranean Sea where there is a higher aragonite saturation state (Ωar), showing that distribution is positively correlated with Ωar. We also observed a resilience of pteropods to higher temperatures and low nutrient conditions, including phosphorous limitation. The higher abundance of pteropods in ultra-oligotrophic conditions (eastern Mediterranean Sea) suggests that this organism can play an important role as the prime calcifying zooplankton within specific oligotrophic regions.