Transplantation of a habitat-forming species as a conservation/restoration measure: the case of the Mediterranean pen shell Pinna nobilis

Coastal development, resulting in habitat loss or degradation, threatens many sessile marine species. The pen shell Pinna nobilis is an endemic, long-lived Mediterranean species and one of the largest bivalves in the world,... [ view full abstract ]

Coastal development, resulting in habitat loss or degradation, threatens many sessile marine species. The pen shell Pinna nobilis is an endemic, long-lived Mediterranean species and one of the largest bivalves in the world, reaching up to 120 cm in shell length. As a suspension-feeding habitat-former it provides important biogeochemical functions of water clarification and biodeposition and  enhances local biodiversity. To avoid smothering of this strictly protected species during construction of a new nautical centre in the Pula Harbour (North Adriatic Sea), we transplanted a total of 184 pen shells to the nearby Brijuni MPA and tested the effect of location, habitat type, depth and density on their survival and growth during 1 year. The pen shell transplantation was confirmed as an effective restoration method, resulting in generally high though habitat-dependent transplant survival and increased function and services of the host habitat. Building upon our and previous transplantation actions, we summarize reasons for restoration success/failure and estimate related costs. Besides being the first official case in Croatia to implement transplantation of a sessile marine species as a measure prescribed by the environmental impact assessment, this action additionally offered a compelling case for the citizen-science. In the light of recently reported pen shell mass mortality events due to a rapidly spreading disease, every effort should be made to minimize more manageable impact in situ (e.g. of costal construction, anchoring, trawling, illegal extraction) in order to ensure maintenance of its populations relaying on survival of adults.