Habitat value of Sydney rock oyster (Saccostrea glomerata) reefs on soft sediments

Abstract

Estimates of the ecological and economic value of ecosystems can provide important information for the prioritisation of conservation and restoration actions. Oyster reefs that were once common in temperate coastal waters have now been largely degraded or lost. Oyster reefs provide a suite of ecological services, including habitat and a food supply for a range of other species. In Australia, there is growing interest in oyster reef restoration, but there are knowledge gaps with regard to their structure and habitat value. Here, we describe the structure of eight remnant Sydney rock oyster (Saccostrea glomerata) reefs and estimate the density, biomass, productivity and composition of mobile macroinvertebrate and infaunal communities associated with them. The oyster reefs had a distinct assemblage of macroinvertebrates, with fivefold higher density of larger (≥2mm) macroinvertebrates, fivefold higher biomass and almost fivefold higher productivity, than that of adjacent bare sediments. The productivity of infaunal communities was twice as high under oyster reefs than in adjacent bare sediments. Therefore, S. glomerata reef restoration is likely to provide important habitat for macroinvertebrate communities and boost local secondary production.

Facilitation cascades create a predation refuge for biodiversity in a novel connected habitat

“…Given that estuarine mollusks can occupy large areas of bare sediment and are often colonized by algae (Inglis 1994, Guti errez et al 2003, we suggest that this facilitation cascade is likely in other systems. While our study considered mollusks with a patchy distribution occupying bare sediment, many mollusks in estuaries form aggregated patches (e.g., oysters and mussels; McLeod et al 2014McLeod et al , 2019. These "reef"-forming species will also likely facilitate algae, although the spatial arrangement of the algae is likely to differ compared to algae on isolated mollusks.…”

The value and opportunity of restoring Australia's lost rock oyster reefs

“…Within this range, S. glomerata populations aggregate at high density where their shells cement together to form three‐dimensional structures composed of living oysters and dead shell remains. These structures range from large consolidated remnant reefs (up to approximately 5,000 m −2 in Port Stephens) that reach heights of approximately 0.5 m above substrate (Hunter River, McLeod et al ), to aggregations of numerous small clumps of oysters dispersed over sedimentary flats (Fig. A & B).…”

“…polychaetes, platyhelminthes, and amphipods) is commonly determined by the presence of S. glomerata (McAfee et al , ). Similarly, on sedimentary shorelines, remnant S. glomerata reefs can support five times the macroinvertebrate productivity than surrounding soft sediment and facilitate biodiverse infaunal communities (McLeod et al ). These benefits extend beyond the immediate confines of S. glomerata reefs; many transient predators (e.g.…”

“…Restoration of the oyster species that historically formed reefs in Australia is now being discussed as an ecosystem-based management approach for restoring lost ecological function (Gillies et al 2015(Gillies et al , 2017McLeod et al 2018). Restoring oyster reefs can provide numerous ecological services: improved water quality and nutrient cycling; shoreline stabilization; food and habitat provision for associated communities; and increased fisheries productivity, to name a few.…”

Can early exposure to stress enhance resilience to ocean warming in two oyster species?

“…O. angasi are mostly found subtidally in comparatively stable thermal conditions [30]. These species are both currently the focus of reef restoration efforts along the south eastern coastline of Australia [31, 32] and are known to be vulnerable to acidification [33,34,35] and warming [33, 36]. South-eastern Australia receives warmer waters from the Coral Sea via the East Australian Current (EAC), which is strengthening [37, 38].…”