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.

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The reintroduction of threatened fish species in areas where wild populations have been depleted due to anthropogenic impacts is an increasingly popular conservation tool and mitigation policy. Despite the importance of fish reintroduction for conservation purposes, little is known about its efficiency. Here, we assessed the viability of reintroduction of the endangered migratory fish, Brycon orbignyanus, in an area of the Upper Uruguay River basin where the species has not been reported for more than 30 years. We released 4000 yearling juveniles in the Pelotas River in 2014 and maintained 400 juveniles in captivity as a control population. After three years, a total of 13 individuals was recaptured, of which, 10 were considered sexually mature with first maturation being recorded in animals larger than 42 cm in total body length. The age–length comparison with a control population growth curve showed that recaptured fish were slightly bigger than those in captivity. Furthermore, important ecological attributes as schooling behavior and dispersal capacity were recorded for all recaptured individuals. Combined, our results suggest that the re-establishment of a self-sustained population of locally extinct species B. orbignyanus in the Pelotas River may be successful if sustained over time and supported by conservation policies.

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