Impacts of sea star predation on mussel bed restoration

Abstract

Predation by sea stars has the potential to cause elevated levels of mortality in reestablished populations of bivalves relative to levels of recruitment. Recent efforts to restore beds of the nearly extirpated green‐lipped mussel within the Hauraki Gulf, New Zealand, resulted in high abundances of sea stars occupying those beds and it is unknown whether predation poses a potential limitation to the success of restoration in this bivalve species. The contribution of predation by sea stars to the mortality of mussels across four experimental mussel beds over a 2‐year period was estimated using data from regular assessments of sea star abundance and an experimentally determined consumption rate of sea stars upon mussels. In addition, the potential size selection of mussels by sea stars was assessed to determine if large sea stars selected for recent settlers. Sea stars' abundance within the mussel beds grew to an average of 0.57 sea stars/m2 within 9 months, remaining at similar levels throughout the study. These predominantly large sea stars were estimated to have consumed 30.1% of the mussels over a 25‐month period, representing a contribution of 40.4% of the mussel mortality. Sea stars predominantly selected for larger mussels, and their predation likely contributes little to any lack in mussel recruitment. Sea star predation is clearly a limiting factor on the survival of transplanted adult mussels and the present study highlights the need to continually assess predation risk to determine if remediation is necessary for the persistence of the restored beds.

Testing habitat suitability for shellfish restoration with small‐scale pilot experiments

“…In addition, these sea stars preferentially targeted the restored beds, as there were very few sea stars found in the control plots. These results confirm behavior previously recorded in a mussel restoration effort in the Hauraki Gulf of the North Island of New Zealand, with starfish predation attributed to 30% of the total loss of the restored mussels (Wilcox & Jeffs, 2019). High densities of these sea stars can commonly be found underneath marine farms (Inglis & Gust, 2003), likely feeding on mussels dropped during the harvesting and cleaning process, which may explain their high abundance at Grant Bay as that location was ca.100 m from a marine farm.…”

“…In comparison, Te Mara was over 2000 m from the nearest marine farm and experienced the lowest predation, while the other three locations ranged from 400 to 1000 m from a marine farm. Elevated winter predation activity of this sea star (Wilcox & Jeffs, 2019) may explain the higher numbers of sea stars sampled on the restored mussels in June (i.e., Austral mid‐winter) for both years of sampling. Sea stars were less abundant at locations with increasing mud content, a finding that could help explain historical patterns of mussel abundance in the inner parts of Pelorus Sound (Flaws, 1975; Stead, 1969).…”

Biodiversity associated with restored small-scale mussel habitats has restoration decision implications

“…This was particularly evident for mobile epifauna, such as sea cucumbers, cat's eye snails, eleven-armed and cushion seastars, that were all found in higher abundances in the mussel plots, indicating a preference for this restored habitat and the increased food availability it provides. For example, sea cucumbers were likely attracted to mussel plots by increases in organic matter (Slater et al 2011;Zamora and Jeffs 2011;Sea et al 2022) and eleven-arm seastars are known mussel predators (Wilcox and Jeffs 2019). These organisms appeared to have migrated into the mussel habitats judging from their large observed sizes.…”

“…To aid in the restored mussel survival the seastars were collected and relocated throughout the sampling period, which may have influenced the overall epifaunal numbers. However, the observed continued migration of seastar predators into these small-scale trial plots indicate that it is important to consider location selection for restoration because proximity of sources of mussel predators may impact restoration success (Wilcox and Jeffs 2019).…”

“…1 Locations of the four experimental mussel habitats in Pelorus Sound, New Zealand mussels was calculated by taking the proportion of live mussels out of the total of both live and dead mussels recorded for each quadrat. As eleven-armed sea stars, Coscinasterias muricata, are a threat to restored mussel survival in New Zealand (Paul-Burke and Burke 2013;Wilcox and Jeffs 2019), they were collected and removed after the deployment, 1, 5-and 13-month sampling events.…”