The pen shell Pinna nobilis is a critically endangered bivalve threatened by mass mortality events throughout the Mediterranean, but the Alfacs Bay (Ebro Delta, Spain) still hosts many healthy individuals.

This study assessed the main factors controlling recruitment patterns in this locality, including gonadal development and abundance of critical life-stages, as well as the effect of environmental factors.

The results obtained from growth records from empty shells suggested a single major peak of recruitment during a period of 11 years. While larval collectors deployed in the area showed no larval settlement and the availability of planktonic larvae was very low.

The authors propose that given the large size of the population and the wide breeding period observed, planktonic processes causing larval mortality such as freshwater discharges from the locally important rice agriculture could possibly account for patterns of low larval availability.

Prado et al. (2019) Breeding, planktonic and settlement factors shape recruitment patterns of one of the last remaining mayor population of Pinna nobilis within Spanish waters. Hydrobiologia doi:10.1007/s10750-019-04137-5