Aerial exposure and critical temperatures limit the survival of restored intertidal mussels

Site selection is one of the biggest challenges affecting coastal restoration success, and can be particularly difficult in the intertidal zone, where species are often living close to their physiological thermal limits. Climate change is causing atmospheric and marine heat waves, with the summer of 2023 having the highest ever recorded global average temperatures. This changing climate, along with other intertidal stressors, increases the difficulty for managers to choose restoration locations in the intertidal zone. In this study, green-lipped mussels (Perna canaliculus) were transplanted into the intertidal zone in a series of 12 plots (9 m(2)) to examine the in situ influence of temperature on mussel survival over a 6-month period. The plots were deployed at varying intertidal heights with differing periods of aerial exposure and temperature. Six months post-deployment the plots had highly variable mussel survival with a range of 0-95%. Results showed that temperature, specifically hours exceeding 25 degrees C, had a negative relationship with mussel survival, and reducing aerial exposure reduces the number of hours exposed to temperatures above 25 degrees C in the summer months. This study demonstrates the utility of deploying temperature loggers by restoration practitioners prior to restoration trials to determine localized variances in temperature and exposure that may aid in site selection in the intertidal zone. In a warming world, our findings illustrate the importance of understanding the potentially critical fine-scale interplay between temperature and exposure time in intertidal shellfish restoration.