Stable isotope analyses reveal major nutritional deficiencies in captive vs. field juvenile individuals of Pinna nobilis.

The pen shell, Pinna nobilis L. is critically endangered by the spread of a haplosporidan parasite. Stable isotopes have been shown an association with dietary assimilation, trophic level, and body condition, and can provide valuable information for ex situ conservation and breeding. In this context, the aim of this study was to investigate the nutritional status of individuals using δ13C and δ15N patterns across pen shell body tissues as tracers of elemental incorporation from treatment diets based on commercial gels and living phytoplankton and/or sediment. Further comparisons were also conducted with field animals and diets to better understand nutritional needs. Captive individuals, were enriched in δ13C and δ15N (~18.9 and 1.3‰, respectively), suggesting severe nutritional stress and utilization of own N and C pools, especially muscle. The mixing model for field individuals evidenced a large contribution from the zooplankton fraction (34.9%), which was further confirmed by experimental feeding with Artemia nauplii.

Pinna nobilis in suboptimal environments are more tolerant to disease but more vulnerable to severe weather phenomena.

We examined a disease outbreak of the fan mussel, Pinna nobilis (L.), in the Alfacs Bay (South Ebro Delta, Spain) during a period of two years in three zones exposed to a summer salinity gradient resulting from agricultural freshwater discharges and distance to the open sea. Long-term monitoring was also conducted in Fangar Bay (North Ebro Delta), featuring lower salinities and no evidence of disease. Results showed that the salinity gradient of Alfacs Bay (37.4-35.7) was associated to cumulative mortality (100% near the mouth, 43% in middle regions, and 13% in inner regions), thus hindering the spread of pathogens. Young specimens showed to be more tolerant to disease than large adults but become vulnerable over time. In Fangar Bay, lower salinities (30.5-33.5) prevented the disease but individuals were highly vulnerable to Storm Gloria which caused 60% mortality in 3 weeks, and ~100% in 6 weeks.