Integrated multi-trophic aquaculture mitigates the effects of ocean acidification: Seaweeds raise system pH and improve growth of juvenile abalone

Integrated multi-trophic aquaculture (IMTA) has the potential to enhance growth, reduce nutrient loads, and mitigate environmental conditions compared to traditional single-species culture techniques. The goal of this project was to develop a land-based system for the integrated culture of seaweeds and shellfish, to test the efficacy of integrated versus non-integrated designs, and to assess the potential for IMTA to mitigate the effects of climate change from ocean acidification on shellfish growth and physiology. We utilized the red abalone (Haliotis rufescens) and the red seaweed dulse (Devaleraea mollis) as our study species and designed integrated tanks at three different recirculation rates (0%, 30%, and 65% recirculation per hour) to test how an integrated design would affect growth rates of the abalone and seaweeds, modify nutrient levels, and change water chemistry. We specifically hypothesized that IMTA designs would raise seawater pH to benefit calcifying species. Our results indicated that juvenile abalone grew significantly faster in weight (22% increase) and shell area (11% increase) in 6 months in tanks with the highest recirculation rates (65%). The 65% recirculation treatment also exhibited a significant increase in mean seawater pH (0.2 pH units higher) due to the biological activity of the seaweed in the connected tanks. We found a significant positive relationship between the mean pH of seawater in the tanks and juvenile abalone growth rates across all treatments. There were no significant differences in the growth of dulse among treatments, but dulse growth did vary seasonally. Seawater phosphate and nitrate concentrations were depleted in the highest recirculation rate treatment, but ammonium concentrations were elevated, likely due to the abalone effluent. Overall, our results indicate that there are benefits to IMTA culture of seaweeds and abalone in terms of improving growth in land-based systems, which will reduce the time to market and buffer commercial abalone operations against the effects of ocean acidification during vulnerable early life stages

Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends

Recent trends in Southern Ocean (SO) climate—of surface cooling, freshening, and sea ice expansion—are not captured in historical climate simulations. Here we demonstrate that the addition of a plausible increase in Antarctic meltwater to a coupled climate model can produce a closer match to a wide range of climate trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model to compute “climate response functions” (CRFs) for the addition of meltwater. These imply a cooling and freshening of the SO, an expansion of sea ice, and an increase in steric height, all consistent with observations since 1992. The CRF framework allows one to compare the efficacy of Antarctic meltwater as a driver of SO climate trends, relative to greenhouse gas and surface wind forcing. The meltwater CRFs presented here strongly suggest that interactive Antarctic ice melt should be included in climate models