Spatial variation in the biotic and abiotic filters of oyster recruitment: Implications for restoration

Abstract

1. Attempts to restore marine ecosystems are increasing, but the success of projects remains variable. For marine invertebrates, the establishment of selfsustaining populations requires a larval supply as well as conditions that permit recruitment.2. Abiotic and biotic conditions that determine recruitment can vary across environmental gradients and have opposing or reinforcing effects. We assessed how predation and tidal inundation influence recruitment of the reef-forming oyster, Saccostrea glomerata, at 15 sites, 5 estuaries and 8 degrees of latitude in eastern Australia.3. Oysters recruited to all 15 sites, but their density displayed spatially variable effects of tidal inundation and caging. Effects of tidal inundation and caging were weakest at the two lower-latitude estuaries where recruitment was low overall, average temperature and turbidity were high and dissolved oxygen low. 4. At higher-latitude estuaries, where abiotic conditions were more favourable for recruitment, recruit density displayed tidal elevation gradients that were dependent on caging and time. Initially, recruit density decreased with tidal inundation (and exposure to finfish predators), in the uncaged but not the caged treatment. However, over time the elevation gradient disappeared, and recruitment and survival of oysters was greater in caged than uncaged treatments irrespective of elevation. Synthesis and applications.Our results suggest that both abiotic (i.e. temperature, turbidity and dissolved oxygen) and biotic (i.e. predation) factors can negatively influence oyster recruitment and, hence, restoration success. Consequently, oyster reef restoration projects should be planned to prioritise sites with low turbidity, high dissolved oxygen and low predation unless these stressors can be mitigated. Restoration projects that are designed with knowledge of local stressors are more likely to be successful.

Complexity–biodiversity relationships on marine urban structures: reintroducing habitat heterogeneity through eco-engineering

“…Other types of stressors, such as contaminants and propagule supply, have been found to mediate complexity effects [52,53]. Second, effects of predation may be greater on the low than the high shore, owing to the greater inundation time enhancing predation risk from finfish predators [54]. Third, the differing configurations of panels on the low, mid and high shore of our study site may produce differential effects.…”

Habitat‐setting affects biodiversity while predation determines oyster survival on experimental oyster reefs

“…To determine treatment effects on oyster predation, eight juvenile S. glomerata (2–4 cm in shell length; sourced from the Port Stephens Fisheries Institute breeding program) were placed on top of the oyster shell in each unit during unit deployment. Juvenile oysters were used as they are vulnerable to predation (Gribben et al 2020; Esquivel‐Muelbert et al 2022) and are used to seed restored reefs (Geraldi et al 2013).…”

“…seagrass, mangroves, and unvegetated sediments). Both predation and abiotic factors can strongly affect oyster recruitment and survival (Esquivel-Muelbert et al 2022) and unsuitable conditions (e.g. high sedimentation) have led to restoration failures (Bayraktarov et al 2016).…”

“…Predation can also vary across landscapes (Esquivel-Muelbert et al 2022) with implications for the survival of foundation species (Carroll et al 2015) and the composition of their associated communities (Micheli & Peterson 1999). Across a landscape, transient predators may maintain consistent amounts and rates of predation, unlike predators which are limited to or more abundant in specific habitats.…”

Aerial exposure tolerance of juvenile flat oysters (Ostrea angasi) depends on shell length and air temperature

“…Exploring factors that can influence the survival of biogenic reef‐forming shellfish species in the intertidal zone is increasingly being considered within a restoration context (e.g. Saccostrea glomerata : Esquivel‐Muelbert et al 2022; Perna canaliculus : Benjamin et al 2023; Toone et al 2023). Although intertidal habitats are physiologically stressful, with tidal cycles bringing periodic desiccation and rapid changes in temperature (Little & Kitching 1996; Somero 2002), the intertidal zone could be a complementary avenue for O. angasi restoration for several reasons.…”