Photosynthetic epibionts and endobionts of Pacific oyster shells from oyster reefs in rocky versus mudflat shores

Abstract

The Pacific oyster, Crassostrea gigas (Thunberg), is the main bivalve species cultivated in the world. With global warming enabling its reproduction and larval survival at higher latitudes, this species is now recognized as invasive and creates wild oyster reefs globally. In this study, the spatial distribution of photosynthetic assemblages colonizing the shells of wild C. gigas was investigated on both a large scale (two contrasting types of reefs found in mudflats and rocky areas) and a small scale (within individual shells) using a hyperspectral imager. The microspatial distribution of all phototrophs was obtained by mapping the Normalized Difference Vegetation Index (NDVI). Second derivative (δδ) analyses of hyperspectral images at 462, 524, 571 and 647 nm were subsequently applied to map diatoms, cyanobacteria, rhodophytes and chlorophytes, respectively. A concomitant pigment analysis was carried out by high performance liquid chromatography and completed by taxonomic observations. This study showed that there was high microalgal diversity associated with wild oyster shells and that there were differences in the structure of the phototropic assemblages depending on the type of reef. Namely, vertically-growing oysters in mudflat areas had a higher biomass of epizoic diatoms (hyperspectral proxy at δδ462 nm) and were mainly colonized by species of the genera Navicula, Nitzschia and Hippodonta, which are epipelic or motile epipsammic. The assemblages on the horizontal oysters contained more tychoplanktonic diatoms (e.g. Thalassiosira pseudonana, T. proschkinae and Plagiogrammopsis vanheurckii). Three species of boring cyanobacteria were observed for both types of reef: Mastigocoleus testarum, Leptolyngbya terrebrans, and Hyella caespistosa, but the second derivative analysis at 524 nm showed a significantly higher biomass for the horizontally-growing oysters. There was no biomass difference for the boring chlorophyte assemblages (δδ647 nm), with two species: Eugomontia testarum and Ostreobium quekettii observed for both types of reef. This study shows that oyster shells are an idiosyncratic but ubiquitous habitat for phototrophic assemblages. The contribution of these assemblages in terms of biomass and production to the functioning of coastal areas, and particularly to shellfish ecosystems, remains to be evaluated.

Microphytobenthos Biomass and Diversity Mapping at Different Spatial Scales with a Hyperspectral Optical Model

“…Kazemipour et al [25] used this iterative method of [43] to estimate η from R and T by a loop between Equations (6), (7) and Equation 8being initialized to 1.…”

“…Diatoms belong to a class of microalgae known for their richness in carotenoid pigments [6] giving a golden-brown color characteristic at the sediment surface and forming dense biofilms in the first millimeters of mudflat sediment. Motile diatoms (epipelic, mud-dwelling) typically form these biofilms only during low tide periods showing movement synchronization with tidal periods [3,7,8].…”

Trophic niche of the invasive gregarious speciesCrepidula fornicata, in relation to ontogenic changes

“…The high percentages of chl b and neoxanthin, as well as the Chl b / Chl a ratio in the biofilm also suggest that chlorophytes were abundant on shells (Brotas and Plante-Cuny, 2003). While these results were not supported by FA (e.g., 18:3n-3 or 18:4n-3 characterizing chlorophytes, Fleurence et al 1994), mollusk shells are currently inhabited by microchlorophytes or macrochlorophytes propagules (Barillé et al, 2017;Mineur et al, 2007). FA characterizing the biofilm were 18:0 and 20:4n-6.…”

Understanding decay in marine calcifiers: Micro‐CT analysis of skeletal structures provides insight into the impacts of a changing climate in marine ecosystems

“…The methods described here could also be used to study the nature of biotic interactions between ubiquitous endolithic microbes and their calcified hosts. These microbes play an important role in primary production and biogeochemical cycling (Mason et al, 2009;Tribollet, Langdon, Golubic, & Atkinson, 2006), including the exchange of nitrogen and carbon with their host (Barille et al, 2017;Pernice et al, 2019). Different skeletomorphs will impose restrictions on the biomass and composition of this community, through limitations in physical space and/or hydrodynamic diffusion of pore water; this variation can be modelled using these µCT analyses.…”