First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)

Abstract Pteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2 concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropod Creseis acicula Rang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered the C. acicula bloom, rather than global atmospheric CO2 levels.