Regional environmental variation and local species interactions influence biogeographic structure on oyster reefs

A global synthesis of predation on bivalves

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer-reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non-native bivalves and non-native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions.

Meta-analysis of ecosystem services associated with oyster restoration

Restoration of foundation species promises to reverse environmental degradation and return lost ecosystem services, but a lack of standardized evaluation across projects limits understanding of recovery, especially in marine systems. Oyster reefs are restored to reverse massive global declines and reclaim valuable ecosystem services, but the success of these projects has not been systematically and comprehensively quantified. We synthesized data on ecosystem services associated with oyster restoration from 245 pairs of restored and degraded reefs and 136 pairs of restored and reference reefs across 3500 km of U.S. Gulf of Mexico and Atlantic coastlines. On average, restoration was associated with a 21-fold increase in oyster production (mean log response ratio = 3.08 [95% confidence interval: 2.58-3.58]), 34-97% enhancement of habitat provisioning (mean community abundance = 0.51 [0.41-0.61], mean richness = 0.29 [0.19-0.39], and mean biomass = 0.69 [0.39-0.99]), 54% more nitrogen removal (mean = 0.43 [0.13-0.73]), and 89-95% greater sediment nutrients (mean = 0.67 [0.27-1.07]) and organic matter (mean = 0.64 [0.44-0.84]) relative to degraded habitats. Moreover, restored reefs matched reference reefs for these ecosystem services. Our results support the continued and expanded use of oyster restoration to enhance ecosystem services of degraded coastal systems and match many functions provided by reference reefs.

Oyster reef restoration facilitates the recovery of macroinvertebrate abundance, diversity, and composition in estuarine communities

Historic declines in oyster populations have resulted in diminished production of ecosystem services and habitat function in many estuaries. Due to the important role of oysters in ecosystem function, scientists and resource managers have employed oyster reef restoration to mitigate declines, recover essential ecosystem services, and better habitat function. Yet, there are knowledge gaps regarding the impact of restoration efforts on ecologically valuable mid-trophic level organisms inhabiting these systems. To address this knowledge gap, here we quantify macroinvertebrate species abundance, community diversity, and composition on experimental restored oyster reefs before and after restoration, and from live (positive control) and dead (negative control) reefs in the Indian River Lagoon, Florida. Species diversity and composition on restored reefs shifted towards states similar to live (positive control) reefs within 12 months of restoration. Recovery of species abundance occurred within 18 months of restoration. The results presented herein quantify the effect of restoration on resident macroinvertebrates and provide timelines of recovery for each attribute of these communities. Further, this study presents an actionable and transferable framework for identifying effective single-species metrics of restoration success across ecosystems. The application of this framework will provide managers and researchers with tools to improve the efficiency and efficacy of post-restoration monitoring. By doing so, this study contributes significantly to the improvement of broader restoration practices in an era of unprecedented habitat loss.