ALBERT

Description: An ex situ experimental mesocosm system was employed to test the effects of climate change drivers temperature, salinity, and reduced light on Arctic kelp communities in Ny-Ålesund, Svalbard from 03/07/2021 –26/08/2021. Three experimental conditions (with 3x replicates) manipulating temperature and salinity as offset values from a dynamic real-time control condition were used to increase temperature on the order of +3.3 and +5.3 °C, freshening by a decrease of ~ 4 and ~ 5 in salinity, along with a static irradiance attenuation at 30 and 50 %. In each mesocosm, oxygen (% O2, temperature, salinity, and flow rate were monitored minutely for 2 months using in situ optical and conductivity sensors paired with flow meters plumbed to the incoming water line. Data were logged on a microSD card. The collected environmental temperature and salinity data were paired with O2 concentration measured during closed incubations which occurred weekly over the experimental period to assess the effects on kelp community metabolism.

Description: Ocean acidification results in co-varying inorganic carbon system variables. Of these, an explicit focus on pH and organismal acid–base regulation has failed to distinguish the mechanism of failure in highly sensitive bivalve larvae. With unique chemical manipulations of seawater we show definitively that larval shell development and growth are dependent on seawater saturation state, and not on carbon dioxide partial pressure or pH. Although other physiological processes are affected by pH, mineral saturation state thresholds will be crossed decades to centuries ahead of pH thresholds owing to nonlinear changes in the carbonate system variables as carbon dioxide is added. Our findings were repeatable for two species of bivalve larvae could resolve discrepancies in experimental results, are consistent with a previous model of ocean acidification impacts due to rapid calcification in bivalve larvae, and suggest a fundamental ocean acidification bottleneck at early life-history for some marine keystone species.

Description: Photosynthesis and respiration are vital biological processes that shape the diurnal variability of carbonate chemistry in nearshore waters, presumably ameliorating (daytime) or exacerbating (nighttime) short-term acidification events, which are expected to increase in severity with ocean acidification (OA). Biogenic habitats such as seagrass beds have the capacity to reduce CO2 concentration and potentially provide refugia from OA. Further, some seagrasses have been shown to increase their photosynthetic rate in response to enriched total CO2 (TCO2). Therefore, the ability of seagrass to mitigate OA may increase as concentrations of TCO2 increase. In this study, we exposed native Zostera marina and non-native Zostera japonica seagrasses from Padilla Bay, WA (USA) to various levels of irradiance and TCO2. Our results indicate that the average maximum net photosynthetic rate (Pmax) for Z. japonica as a function of irradiance and TCO2 was 3x greater than Z. marina when standardized to chlorophyll (360 ± 33 μmol TCO2 mg/chl/h and 113 ± 10 μmol TCO2 mg/chl/h, respectively). Additionally, Z. japonica increased its Pmax ~50% when TCO2 increased from 1,770 to 2,051 μmol TCO2/kg. In contrast, Z. marina did not display an increase in Pmax with higher TCO2, possibly due to the variance of photosynthetic rates at saturating irradiance within TCO2 treatments (coefficient of variation: 30–60%) relative to the range of TCO2 tested. Our results suggest that Z. japonica can affect the OA mitigation potential of seagrass beds, and its contribution may increase relative to Z. marina as oceanic TCO2 rises. Further, we extended our empirical results to incorporate various biomass to water volume ratios in order to conceptualize how these additional attributes affect changes in carbonate chemistry. Estimates show that the change in TCO2 via photosynthetic carbon uptake as modeled in this study can produce positive diurnal changes in pH and aragonite saturation state that are on the same order of magnitude as those estimated for whole seagrass systems. Based on our results, we predict that seagrasses Z. marina and Z. japonica both have the potential to produce short-term changes in carbonate chemistry, thus offsetting anthropogenic acidification when irradiance is saturating.

Description: Arctic marine ecosystems are experiencing rapid environmental change with respect to warming. This is leading to an increased frequency, duration, and intensity of marine heatwaves. The impact of these stochastic heatwave events have the potential to negatively effect temperature-sensitive, habitat forming, kelp, that exist in the lower Arctic region. We tested the potential impacts of two heatwave events on mixed kelp communities occurring in the lower Arctic by conducting a 1-month ex situ mesocosm experiment in Tromsø, Norway. Each mesocosm was stocked with ~ 2.5 kg fw (fresh weight) of kelp, 200 g fw of snails and mussels, and ~ 750 g of sea urchins. Three experimental conditions were tested: a constant high temperature which was + 1.76°C above a dynamic control, and two heatwave scenarios. Scenario 1 was a long duration at + 2.8°C above the control for 2 weeks, and scenario 2 was a high frequency and magnitude treatment with conditions + 3.8°C above the control. This occurred at two peaks that were one weak apart and returned to + 1.76°C in-between. Three-hour incubations were performed to examine net community productivity (NCP) for the mixed kelp communities. We identified that both heatwave scenarios diminished the total gross production over the experimental period compared to the control and between scenario 1 and scenario 2. Scenario 1 appeared to exhibit the lowest total gross community production over the experimental period.