Towards a sampling design for characterizing habitat-specific benthic biodiversity related to oxygen flux dynamics using Aquatic Eddy Covariance

Abstract

The Aquatic Eddy Covariance (AEC) technique has emerged as an important method to quantify in situ seafloor metabolism over large areas of heterogeneous benthic communities, enabling cross-habitat comparisons of seafloor productivity. However, the lack of a corresponding sampling protocol to perform biodiversity comparisons across habitats is impeding a full assessment of marine ecosystem metabolism. Here, we study a range of coastal benthic habitats, from rocky-bed communities defined by either perennial macroalgae or blue mussel beds to soft-sediment communities comprised of either seagrass, patches of different macrophyte species or bare sand. We estimated that the maximum contribution to the AEC metabolic flux can be found for a seafloor area of approximately 80 m2 with a 5 meter upstream distance of the instrument across all the habitats. We conducted a sampling approach to characterize and quantify the dominant features of biodiversity (i.e., community biomass) within the main seafloor area of maximum metabolic contribution (i.e., gross primary production and community respiration) measured by the AEC. We documented a high biomass contribution of the macroalgal Fucus vesiculosus, the seagrass Zostera marina and the macroinvertebrate Mytilus edulis to the net ecosystem metabolism of the habitats. We also documented a significant role of the bare sediments for primary productivity compared to vegetated canopies of the soft sediments. The AEC also provided insight into dynamic short-term drivers of productivity such as PAR availability and water flow velocity for the productivity estimate. We regard this study as an important step forward, setting a framework for upcoming research focusing on linking biodiversity metrics and AEC flux measurements across habitats.

Seasonal ecosystem metabolism across shallow benthic habitats measured by aquatic eddy covariance

“…We developed a sampling protocol to quantify dominant features of seafloor biodiversity within the eddy covariance flux footprint (Rodil et al ). The extracted samples were used to estimate the standing biomass (g C m −2 ) of the main phototrophic components and macrofauna of each habitat using conversion ratios for dry weight (macrophytes), ash‐free dry weight (macrofauna), or chlorophyll a (microphytobenthos) (Supporting Information Section S1).…”

Macrofauna communities across a seascape of seagrass meadows: environmental drivers, biodiversity patterns and conservation implications

“…S1) using 100 mL-syringes (Ø = 3.5 cm, 10 cm deep) for organic matter and pigments (surface sediment, 1 cm layer), and grain size (the rest of the sediment). This protocol ensured that a major representation of the key biodiversity components across sites were sampled (Rodil et al 2019).…”

Technical note: Measurements and data analysis of sediment–water oxygen flux using a new dual-optode eddy covariance instrument

“…To improve the reliability of the flux measurements, eddy covariance instruments with dual microelectrodes were developed (e.g. Attard et al, 2014;McGinnis et al, 2011;Rodil et al, 2019;de Froe et al, 2019;Rovelli et al, 2015) An alternative to the electrochemical microelectrodes are optical sensors (optodes or optrodes) that use the luminescence characteristics of an oxygen-sensitive dye for oxygen concentration measurements (Klimant et al, 1995;Holst et al, 1998;Bittig et al, 2018;Wang and Wolfbeis, 2014). Optodes consume no oxygen and may have very low or no stirring sensitivity (Holtappels et al, 2015;Berg et al, 2016.…”