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1. Foundation species loss alters multiple ecosystem functions within temperate tidepool communities

   https://doi.org/10.3354/meps13978  

   Fields, JB ; Silbiger, NJ ( February 2022 , Marine Ecology Progress Series)

   Foundation species, which help maintain habitat and ecosystem functioning, are declining due to anthropogenic impacts. Within the rocky intertidal ecosystem, studies have investigated the effects of foundation species on community structure and some resource fluxes; however, how intertidal foundation species loss will affect multiple facets of ecosystem functioning in concert remains unknown. We studied the direct and indirect effects of foundation species loss of mussels Mytilus californianus and surfgrass Phyllospadix spp. on community structure, fluxes (light, temperature, dissolved oxygen [DO], dissolved inorganic nutrients, pH T ), and ecosystem metabolism (net ecosystem calcification [NEC] and net ecosystem production [NEP]) in central Oregon using in situ tide pool manipulations. Surfgrass loss increased microalgae cover, increased average maximum light by 142% and average maximum temperature by 3.8°C, increased DO and pH T values, and indirectly increased NEP and NEC via increased maximum temperature and pH T respectively. Mussel loss increased microalgae cover, increased average maximum light by 5.8% and average maximum temperature by 1.3°C, increased DO and pH T values, and indirectly increased NEP via increased producer cover. Shifts in baseline nutrient concentrations and temperature values from coastal upwelling influenced ecosystem metabolism in pools with intact foundation species. Our results indicate that as communities respond to foundation species loss, ecosystem functioning depends on the dominant community present and biologically or physically driven shifts in biogeochemistry. This study highlights the importance of the connection between community and ecosystem ecology in understanding the magnitude of changes occurring with anthropogenically-driven intertidal foundation species loss. 

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2. Ocean acidification effects on in situ coral reef metabolism

   https://doi.org/10.1038/s41598-019-48407-7  

   Doo, Steve S. ; Edmunds, Peter J. ; Carpenter, Robert C. ( August 2019 , Scientific Reports)

   The Anthropocene climate has largely been defined by a rapid increase in atmospheric CO_2,causing global climate change (warming) and ocean acidification (OA, a reduction in oceanic pH). OA is of particular concern for coral reefs, as the associated reduction in carbonate ion availability impairs biogenic calcification and promotes dissolution of carbonate substrata. While these trends ultimately affect ecosystem calcification, scaling experimental analyses of the response of organisms to OA to consider the response of ecosystems to OA has proved difficult. The benchmark of ecosystem-level experiments to study the effects of OA is provided through Free Ocean CO₂Enrichment (FOCE), which we use in the present analyses for a 21-d experiment on the back reef of Mo’orea, French Polynesia. Two natural coral reef communities were incubatedin situ, with one exposed to ambient pCO₂(393 µatm), and one to high pCO₂(949 µatm). Our results show a decrease in 24-h net community calcification (NCC) under high pCO₂, and a reduction in nighttime NCC that attenuated and eventually reversed over 21-d. This effect was not observed in daytime NCC, and it occurred without any effect of high pCO₂on net community production (NCP). These results contribute to previous studies on ecosystem-level responses of coral reefs to the OA conditions projected for the end of the century, and they highlight potential attenuation of high pCO₂effects on nighttime net community calcification.

    

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3. Interannual and Seasonal Drivers of Carbon Cycle Variability Represented by the Community Earth System Model (CESM2)

   https://doi.org/10.1029/2021GB007034  

   Wieder, William R. ; Butterfield, Zachary ; Lindsay, Keith ; Lombardozzi, Danica L. ; Keppel‐Aleks, Gretchen ( September 2021 , Global Biogeochemical Cycles)

   Earth system models are intended to make long‐term projections, but they can be evaluated at interannual and seasonal time scales. Although the Community Earth System Model (CESM2) showed improvements in a number of terrestrial carbon cycle benchmarks, relative to its predecessor, our analysis suggests that the interannual variability (IAV) in net terrestrial carbon fluxes did not show similar improvements. The model simulated low IAV of net ecosystem production (NEP), resulting in a weaker than observed sensitivity of the carbon cycle to climate variability. Low IAV in net fluxes likely resulted from low variability in gross primary productivity (GPP)—especially in the tropics—and a high covariation between GPP and ecosystem respiration. Although lower than observed, the IAV of NEP had significant climate sensitivities, with positive NEP anomalies associated with warmer and drier conditions in high latitudes, and with wetter and cooler conditions in mid and low latitudes. We identified two dominant modes of seasonal variability in carbon cycle flux anomalies in our fully coupled CESM2 simulations that are characterized by seasonal amplification and redistribution of ecosystem fluxes. Seasonal amplification of net and gross carbon fluxes showed climate sensitivities mirroring those of annual fluxes. Seasonal redistribution of carbon fluxes is initiated by springtime temperature anomalies, but subsequently negative feedbacks in soil moisture during the summer and fall result in net annual carbon losses from land. These modes of variability are also seen in satellite proxies of GPP, suggesting that CESM2 appropriately represents regional sensitivities of photosynthesis to climate variability on seasonal time scales.

    

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4. Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

   https://doi.org/10.5194/bg-16-4411-2019  

   Van Dam, Bryce R. ; Lopes, Christian ; Osburn, Christopher L. ; Fourqurean, James W. ( January 2019 , Biogeosciences)

   Abstract. The net ecosystem productivity (NEP) of two seagrassmeadows within one of the largest seagrass ecosystems in the world, FloridaBay, was assessed using direct measurements over consecutive diel cyclesduring a short study in the fall of 2018. We report significant differencesbetween NEP determined by dissolved inorganic carbon (NEPDIC) and bydissolved oxygen (NEPDO), likely driven by differences in air–water gasexchange and contrasting responses to variations in light intensity. We alsoacknowledge the impact of advective exchange on metabolic calculations ofNEP and net ecosystem calcification (NEC) using the “open-water” approachand attempt to quantify this effect. In this first direct determination ofNEPDIC in seagrass, we found that both seagrass ecosystems were netheterotrophic, on average, despite large differences in seagrass netabove-ground primary productivity. NEC was also negative, indicating thatboth sites were net dissolving carbonate minerals. We suggest that acombination of carbonate dissolution and respiration in sediments exceededseagrass primary production and calcification, supporting our negative NEPand NEC measurements. However, given the limited spatial (two sites) andtemporal (8 d) extent of this study, our results may not berepresentative of Florida Bay as a whole and may be season-specific. Theresults of this study highlight the need for better temporal resolution,accurate carbonate chemistry accounting, and an improved understanding ofphysical mixing processes in future seagrass metabolism studies. 

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5. Lateral, Vertical, and Temporal Variability of Seawater Carbonate Chemistry at Hog Reef, Bermuda

   https://doi.org/10.3389/fmars.2021.562267  

   Pezner, Ariel K. ; Courtney, Travis A. ; Page, Heather N. ; Giddings, Sarah N. ; Beatty, Cory M. ; DeGrandpre, Michael D. ; Andersson, Andreas J. ( February 2021 , Frontiers in Marine Science)

   null (Ed.)

   Spatial and temporal carbonate chemistry variability on coral reefs is influenced by a combination of seawater hydrodynamics, geomorphology, and biogeochemical processes, though their relative influence varies by site. It is often assumed that the water column above most reefs is well-mixed with small to no gradients outside of the benthic boundary layer. However, few studies to date have explored the processes and properties controlling these multi-dimensional gradients. Here, we investigated the lateral, vertical, and temporal variability of seawater carbonate chemistry on a Bermudan rim reef using a combination of spatial seawater chemistry surveys and autonomous in situ sensors. Instruments were deployed at Hog Reef measuring current flow, seawater temperature, salinity, pH T , p CO 2 , dissolved oxygen (DO), and total alkalinity (TA) on the benthos, and temperature, salinity, DO, and p CO 2 at the surface. Water samples from spatial surveys were collected from surface and bottom depths at 13 stations covering ∼3 km 2 across 4 days. High frequency temporal variability in carbonate chemistry was driven by a combination of diel light and mixed semi-diurnal tidal cycles on the reef. Daytime gradients in DO between the surface and the benthos suggested significant water column production contributing to distinct diel trends in pH T , p CO 2 , and DO, but not TA. We hypothesize these differences reflect the differential effect of biogeochemical processes important in both the water column and benthos (organic carbon production/respiration) vs. processes mainly occurring on the benthos (calcium carbonate production/dissolution). Locally at Hog Reef, the relative magnitude of the diel variability of organic carbon production/respiration was 1.4–4.6 times larger than that of calcium carbonate production/dissolution, though estimates of net organic carbon production and calcification based on inshore-offshore chemical gradients revealed net heterotrophy (−118 ± 51 mmol m –2 day –1 ) and net calcification (150 ± 37 mmol CaCO 3 m –2 day –1 ). These results reflect the important roles of time and space in assessing reef biogeochemical processes. The spatial variability in carbonate chemistry parameters was larger laterally than vertically and was generally observed in conjunction with depth gradients, but varied between sampling events, depending on time of day and modifications due to current flow. 

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