Spring distribution of shelled pteropods across the Mediterranean Sea

Abstract

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.

Key Environmental Factors Controlling Planktonic Foraminiferal and Pteropod Community’s Response to Late Quaternary Hydroclimate Changes in the South Aegean Sea (Eastern Mediterranean)

“…Of the oceanographic factors typically considered, SST shows the highest explanatory power for the distribution of the planktonic fauna during the Late Quaternary. This is in accordance with previously published studies showing temperature as the dominant factor controlling the biogeography of planktonic foraminifera and pteropods at both global and local scales [61,67,97]. However, the 2 remaining factors (PCA-2, PCA-3) exhibit a bipolar character and could be considered as indicators of the annual stability of the water column.…”

“…Particularly, the down-core scores of the second factor coincide with the δ 13 C and E-index values, indicating that variations in primary productivity have an impact on pteropod abundances. Even though nutrient concentrations are not a limited factor for their distribution [67], our data suggest that fluctuations in nutrients and salinity due to the increased freshwater inputs during the sapropel deposition favor the flourishment of some species (Cavolinia spp., B. chierchiae; Figure 4). Additionally, the third factor suggests that oxygen concentration, and thus the intensity of the oxygen minimum zone (OMZ), are parameters that affect pteropod distribution and particularly the mesopelagic species [66].…”

“…A considerable number of studies (e.g., [33,34,[61][62][63][64][65][66]) have shown that Late Quaternary pteropod assemblages and their distribution pattern in the world oceans have changed with temperature and the overall climatic conditions that also affect the aragonite compensation depth (ACD). Recent studies [67] have shown that modern eastern Mediterranean pteropod communities are found to be more abundant than in those at western Mediterranean Sea. Their abundances are positively correlated with the aragonite saturation state (Ωar), O 2 concentration, pH, salinity and temperature, and negatively correlated with nutrient concentrations [67,68].…”

“…Recent studies [67] have shown that modern eastern Mediterranean pteropod communities are found to be more abundant than in those at western Mediterranean Sea. Their abundances are positively correlated with the aragonite saturation state (Ωar), O 2 concentration, pH, salinity and temperature, and negatively correlated with nutrient concentrations [67,68]. However, pteropod assemblages and their distribution in the Aegean Sea during the Late Quaternary are poorly documented.…”

Ecological Constraints of Plankton Bio-Indicators for Water Column Stratification and Productivity: A Case Study of the Holocene North Aegean Sedimentary Record

“…In contrast, the pteropod distribution pattern does not respond in the same way as planktonic foraminifera to changes in productivity. It is known that nutrient concentration is not a limited factor for their distribution [99], though our data suggest that fluctuations in nutrients and salinity due to the increased freshwater inputs, especially during the sapropel S1 deposition, favor the flourishment of the species B. chierchiae [29]. The stratification factor, on the contrary, affects the pteropod fauna (38%) more than the planktonic foraminifera (16%) (Tables 1 and 2).…”