Turbidity and salinity influence trophic cascades on oyster reefs through modification of sensory performance and facilitation of different predator types

Abstract

Abiotic factors can influence the distribution of organisms through physiological tolerance limits and by affecting their sensory performance in critical life history functions such as foraging or predator avoidance. In estuaries, salinity and turbidity directly influence the distribution of organisms but the indirect, synergistic effects of these factors on trophic interactions and community structure remain obscure. We investigated the effects of salinity and turbidity on oyster reef communities by comparing oyster reef community structure in low vs. high turbidity in consecutive years that varied considerably in rainfall and ambient salinity levels. Turbidity had significant effects in both 2016 and 2017 by interfering with fish foraging ability and consumption. In turbid sites, fish predation decreased by ~21%, crab mesopredators were 11% larger and nearly 5 times more abundant due to reduced top-down control by fish, and oyster reef biodiversity was 12% lower. In 2016, oysters were 350% less abundant in sites with abundant crab predators. However, in 2017, salinity increased, facilitating a new predator (oyster drills Stramonita haemastoma) to emerge onto reefs, and oysters were 7 times less abundant in sites with oyster drills despite having fewer crab predators. Thus, salinity and turbidity can indirectly affect food webs by facilitating different predators and influencing their sensory performance. Turbidity had significant effects on estuarine food webs regardless of salinity levels, and like salinity, turbidity should also be considered in oyster reef restoration and management of estuarine ecosystems.

Variation in the density and body size of a threatened foundation species across multiple spatial scales

“…This study found greater fish predation at Port Hacking than Crookhaven River, which is one of the sites with high density and size of oysters. Moreover, at Hunter River, we would expect predation to be low due to high turbidity at this site as has been observed in other systems (Lunt & Smee 2014; Reustle & Smee 2020). Hence, it is unlikely that differences in rates of predation explain differences in oyster length and density among estuaries.…”

Using standardized fish‐specific autonomous reef monitoring structures (FARMS) to quantify cryptobenthic fish communities

“…These differences were largely driven by epibenthic/epipelagic species such as yellow perch ( Bairdiella chrysoura ) and pinfish ( Lagodon rhomboides ). There is an intuitive incentive for filling sampling units with natural, locally abundant substrates (such as oyster shells or coral rubble), as these units closely resemble the surrounding habitat (Reustle & Smee, 2020; Takada et al, 2016; Valles et al, 2006). However, this precludes the standardization of materials across studies.…”

“…In Texas, thirteen FARMS were deployed among three coastal lagoons on the Gulf coast in early March of 2019. Nine of these were set in shallow water (~1‐2 m depth) and deployed alongside an oyster sampling unit (OSU; or ‘biobox’; Reustle & Smee, 2020). OSUs were 0.25 m 3 and constructed from a wooden frame with a 1 cm 2 mesh bottom holding a volume of sterilized oyster shell equal to five gallons, while the estimated volume for each FARMS was 0.03 m 3 (one cubic foot).…”

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

“…Sediment deposition is a known cause of recruitment failure and generally increases with turbidity. Particularly, sedimentation can render substrate unsuitable for settlement and prevent recent settlers from effectively filtering, leading to high post‐settlement mortality (Reustle & Smee, 2020; Schulte et al., 2009; Soniat et al., 2004). Although temperature was negatively and dissolved oxygen, positively, correlated with oyster recruit density, each remained within the tolerance window for S. glomerata recruitment (O’Connor et al., 2008).…”

“…Sediment deposition is a known cause of recruitment failure and generally increases with turbidity. Particularly, sedimentation can render substrate unsuitable for settlement and prevent recent settlers from effectively filtering, leading to high post-settlement mortality (Reustle & Smee, 2020;Schulte et al, 2009;Soniat et al, 2004)…”