Seasonal metabolism and carbon export potential of a key coastal habitat: The perennial canopy‐forming macroalga Fucus vesiculosus

Abstract

The important role of macroalgal canopies in the oceanic carbon (C) cycle is increasingly being recognized, but direct assessments of community productivity remain scarce. We conducted a seasonal study on a sublittoral Baltic Sea canopy of the brown alga Fucus vesiculosus, a prominent species in temperate and Arctic waters. We investigated community production on hourly, daily, and seasonal timescales. Aquatic eddy covariance (AEC) oxygen flux measurements integrated ~ 40 m2 of the seabed surface area and documented considerable oxygen production by the canopy year‐round. High net oxygen production rates of up to 35 ± 9 mmol m−2 h−1 were measured under peak irradiance of ~ 1200 μmol photosynthetically active radiation (PAR) m−2 s−1 in summer. However, high rates > 15 mmol m−2 h−1 were also measured in late winter (March) under low light intensities < 250 μmol PAR m−2 s−1 and water temperatures of ~ 1°C. In some cases, hourly AEC fluxes documented an apparent release of oxygen by the canopy under dark conditions, which may be due to gas storage dynamics within internal air spaces of F. vesiculosus. Daily net ecosystem metabolism (NEM) was positive (net autotrophic) in all but one of the five measurement campaigns (December). A simple regression model predicted a net autotrophic canopy for two‐thirds of the year, and annual canopy NEM amounted to 25 mol O2 m−2 yr−1, approximately six‐fold higher than net phytoplankton production. Canopy C export was ~ 0.3 kg C m−2 yr−1, comparable to canopy standing biomass in summer. Macroalgal canopies thus represent regions of intensified C assimilation and export in coastal waters.

Technical note: Estimating light-use efficiency of benthic habitats using underwater O&lt;sub&gt;2&lt;/sub&gt; eddy covariance

“…We are grateful to our colleagues at the (Holtappels et al, 2013;Brand et al, 2008) Changes in diffusive boundary layer thickness in cohesive sediments (Kuhl et al, 1996) Sensor stirring sensitivity (Holtappels et al, 2015) Pore-water advection in permeable sediments (Cook et al, 2007;McGinnis et al, 2014) Surface wave influence Reimers et al, 2016) Diel fauna activity (Wenzhofer and Glud, 2004) Sensor response time Berg et al, 2015) Sediment resuspension (Toussaint et al, 2014), Camillini et al In review Internal plant O2 storage, canopy storage, or bubbling (Attard et al, 2019a;Rheuban et al, 2014;Long et al, 2020) Oxidation of anaerobic metabolites in sediments (Fenchel and Glud, 2000) Nutrient availability (Elser et al, 2007) O2 m -2 h -1 ), the photoadaptation parameter Ik (µmol PAR m -2 s -1 ), the initial slope of the curve , and the coefficient of determination (R 2 ). Data modified from Attard et al (2014).…”

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

“…For typical coastal seafloor settings, the estimated length of the footprint ranges from < 10 m for habitats with rough benthic surfaces ( e . g ., oyster beds, [20] or vegetated canopies, [30]) to > 80 m for habitats with smoother surfaces such as bare sediments in unidirectional flows [31] (Fig 4B). The AEC flux signal is not distributed evenly within the footprint area, but most of the flux signal originates from a smaller region (X max ) typically located < 5 m upstream from the instrument (Fig 4B).…”

Wave stress and biotic facilitation drive community composition in a marginal hard‐bottom ecosystem

“…), reducing physical stress (Bertness and Callaway ), supporting gas exchange (Attard et al. ), and increasing resource availability (Norkko et al. , Norling and Kautsky ).…”

“…Foundation species (FS), such as many trees, shrubs, corals, bivalves, macroalgae, and seagrasses, are species that often have a disproportionately large influence on community structure and ecosystem function (Dayton 1975). They are vital for many systems as they have a propensity to increase diversity, biomass, or ecosystem stability through, for example, enlarging niche space (Bulleri et al 2016), enhancing habitat complexity (Kostylev et al 2005), reducing physical stress (Bertness and Callaway 1994), supporting gas exchange (Attard et al 2019), and increasing resource availability (Norkko et al 2006, Norling and. High diversity is important, as rich communities are better equipped with functions that buffer against future changes in the environment, caused by stressors such as climate change, species introductions, or eutrophication.…”