Metabolism of a tide‐dominated reef platform subject to extreme diel temperature and oxygen variations

Abstract

Benthic dissolved oxygen fluxes were measured on the reef flat of Tallon Island, an intertidal reef platform in the Kimberley region of northwestern Australia, for periods of 2 weeks in the wet and dry seasons. This reef flat is strongly tidally forced by semidiurnal tides (spring range > 8 m) and experiences highly asymmetric water level variability, with ebb durations lasting ∼10 h; this results in diel variations in water temperature and dissolved oxygen (DO) concentration (up to ∼11°C and 440 μM, respectively) that are among the most extreme recorded for reefs worldwide. Given the consistent tidal flow patterns, a one‐dimensional control volume approach was used to make continuous Eulerian measurements of net production and community respiration from observed changes in DO within two zones: an inner zone dominated by seagrass and an outer zone dominated by macroalgae. Community respiration (R) was controlled primarily by DO concentration; however, fluxes approached the limits of DO mass transfer at low flow speeds. Estimates of gross primary production (P) suggested that reef communities were able to fix carbon at rates comparable to other tropical seagrass and mixed reef flat communities despite short‐term (∼hours) extremes in light (up to 1800 μmol m−2 s−1) and temperature (> 35°C). Daily net community production fluctuated between net autotrophy and heterotrophy over a ∼15 d period depending on the phase difference between the solar and tidal cycles but was nonetheless metabolically balanced on time scales greater than weeks (P : R = 1.0–1.1).

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

“…Community NEM rates of various seafloor habitats worldwide on (A) daily and (B) annual timescales. Daily NEM (a) mean ± SD (large open symbols) and number of observations ( n ) for datasets that compute the daily NEM from continuous diel measurements over 24 h (Maerl beds: Attard et al [], Martin et al [], and Martin et al []; bare sediments: Attard et al [], Attard et al [], Berg et al [], Chipman et al [], Hume et al [], Rheuban et al [], and Walpersdorf et al []; macroalgae: Gruber et al [] and this study; Seagrass: Ganguly et al [], Gruber et al [], Hume et al [], Lee et al [], Long et al [], Moriarty et al [], Olivé et al [], Pollard and Moriarty [], and Rheuban et al []). Annual data (B) are from studies that consider daily and seasonal NEM when computing the annual estimate (Maerl beds: Attard et al [] and Martin et al []; bare sediments: Attard et al [], Chipman et al [], and Rheuban et al []; Seagrass: Rheuban et al []; Macroalgae: this study).…”

Benthic uptake of phytoplankton and ocean‐reef exchange of particulate nutrients on a tide‐dominated reef

“…a). Previous studies have addressed the hydrodynamics (Lowe et al ), thermodynamics (Lowe et al ), and community productivity (Gruber et al ) of Tallon reef.…”

The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

“…Corals on the reef flat of the Kimberley region have to cope with extended aerial exposure during spring low tides (up to several hours, Figure 2) and periods of stagnant water alternating with strong tidal currents (>10 knots). These physical conditions create extreme fluctuations in environmental parameters, such as temperature (e.g., the well-studied Shell Island where temperature can fluctuate by up to 7 • C daily, Dandan et al, 2015;Schoepf et al, 2015), pH (e.g., Tallon Island where pH can fluctuate from 7.6 to 8.8 units over a spring low tide, Pedersen et al, 2016), dissolved oxygen (Pedersen et al, 2016;Gruber et al, 2017), unusually turbid waters, and monthly SST exceeding 30 • C for several months a year. Despite these extreme conditions, highly diverse coral reefs exist throughout the Kimberley of up to 225 species (Rosser and Veron, 2011;Richards et al, 2015), which are comparable to inshore reefs in the central GBR ∼2 decades ago (Richards et al, 2015).…”

“…Reef flat communities of the Kimberley appear to have adapted their physiology to maintain metabolic balance of photosynthesis-to-respiration (P:R) despite the extreme physicochemical conditions of the reef-flat (Gruber et al, 2017). Furthermore, a seasonal calcification study revealed high resilience of coral calcification to both intertidal and subtidal temperature conditions as branching and massive corals calcified at rates that were comparable to those of similar species at a more typical coral reef 1,200 km to the southwest (Ningaloo Reef; Dandan et al, 2015).…”

“…For example, in the vent sites of Japan, hard corals dominate at 225 µatm, become limited at 831 µatm and are absent at the highest pCO 2 sites (1,465 µatm, Inoue et al, 2013). Similarly, in the Kimberley region, diverse coral communities dominated by branching Acropora exist in tide pools characterized by large diurnal temperature but not pH fluctuations (Dandan et al, 2015), whereas coral cover drops to <10% and Acropora ceases to exist on reef flats where extreme temperature, pH and oxygen fluctuations create a much more extreme environment (Gruber et al, 2017).…”