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.

Where the wild things aren’t: exploring the utility of rapid, small-scale translocations to improve site selection for shellfish restoration

“…However, when left unprotected at certain sites they can quickly be removed by local predators (e.g., by predatory sea stars in their historic range, Wilcox et al, 2018;Benjamin et al, 2023). One-two weeks were considered sufficient to compare the potential impacts of predators and environmental factors on mussel survival to inform site selection criteria as previous work has indicated that predators will remove newly translocated mussels within the first few days following placement on the seafloor (Alder et al, 2020(Alder et al, , 2022.…”

“…• Turbidity (Percent of turbidity-obscured images): Since predator species like Tamure/Australasian snapper (Hereafter Australasian snapper) are visual hunters and suspended sediment can impact mussel filtration rates, the number of turbidity-obscured images recorded for each deployment were included as a proxy for water column turbidity. Previous work has also indicated a positive relationship between the number of turbid images recorded and the number of predators observed, which negatively interact with mussel survival (Alder et al, 2022). All images with < 0.5 m of visibility (i.e., where adjacent mussel groups were not clearly visible) were categorised as turbidityobscured images.…”

“…• sea stars: Patangaroa/eleven-armed sea stars (Coscinasterias muricata; New Zealand, Wilcox and Jeffs, 2019;Paul-Burke et al, 2022;Benjamin et al, 2023). • crabs: European green crab (Carcinus maenas;Netherlands, De Paoli et al, 2015;United States, Whitlow et al, 2003;Floyd and Williams, 2004) Alder et al, 2020Alder et al, , 2022, Whai/ray spp. (New Zealand, Australia, Alder et al, 2020Martinez-Baena et al, 2023).…”

“…Therefore, there is a need to refine methods for understanding the presence and/or movement of mobile predator species that may limit the establishment of founders ahead of expensive, large-scale restoration efforts. There is some indication that methods and timing of translocations may limit predation and improve initial translocated mussel survival (Bertolini et al, 2018;Alder et al, 2022), however less is known about methods to assess the spatial variability of predators at desired restoration sites prior to restoration efforts. There is mounting evidence that the strategic placement of bivalve species can limit predation, such as the installation of euryhaline oyster reefs at less saline locations to limit the impact of freshwater intolerant oyster drills (Johnson and Smee, 2014;Pusack et al, 2019).…”

Diet of snapper (Chrysophrys auratus) in green‐lipped mussel farms and adjacent soft‐sediment habitats

“…This is likely due to the availability of Bivalvia in the benthic habitat at this specific site, as snapper sampled from Rat Island only included 0.15% Bivalvia in their gut contents. Green-lipped mussels have been rarely reported in the gut contents of snapper sampled from natural habitats (Third, 2022;Usmar, 2012), but snapper are known to predate on them when they are available (Alder et al, 2021(Alder et al, , 2022a(Alder et al, , 2022b. Blue mussels have never been recorded in previous snapper diets in New Zealand (Colman, 1972;Drummond, 2020;Godfriaux, 1970;Russell, 1983;Third, 2022;Usmar, 2012).…”