Timing mussel deployments to improve reintroduction success and restoration efficiency

Abstract

The loss of newly translocated species directly contributes to low rates of reintroduction success in both terrestrial and aquatic ecosystems. In this study, experimental reintroductions of green-lipped mussels Perna canaliculus into a shallow coastal habitat were conducted across 5 week-long experimental translocations within a 10 mo period (April 2021-January 2022) to relate temporal variations in predator abundance, predator size, and environmental parameters (water temperature, rainfall, days before/after full moon, turbidity, wind speed, wind direction) to variations in mussel survival. Predator counts from timelapse camera images gathered over the first 4 d after each deployment were used as a proxy for potential predator pressure. Timelapse images (n = 8561) allowed for a census of 2371 individuals from 10 different mobile species, 5 of which were known bivalve predators (Australasian snapper, New Zealand eagle ray, rig shark, octopus, and an unidentifiable ray species), with Australasian snapper contributing to 98% of overall species counts. At the end of the study, mean mussel survival ranged from 0 ± 0 SE% to 56 ± 8 SE% and was best predicted by changes in turbidity and the total number of predators among deployments (R2 = 0.445). Patterns in predator abundance were best explained by time of year and did not share strong correlations among environmental parameters (rho = 0.015). These results suggest that planning deployments of mussels for cooler times of the year when water clarity is high and predator abundance is low may substantially increase immediate survivorship of translocated mussels and improve reintroduction success.