Description: Inducing defenses to deter predators is a necessary process theorized to incur costs. Although studies have investigated defense trade-offs, quantifying trade-offs is challenging and costs are often inferred. Additionally, prey employ strategies to reduce costs, making costs difficult to predict. Our purpose was to investigate induced defense costs by characterizing the defense mechanisms and costs in eastern oysters (Crassostrea virginica). In the field (summer 2014; 28.13°N, 96.98°W), newly-settled oysters reared under field conditions and assigned to control or predator (blue crab, Callinectes sapidus) conditions, were tested for shell weight and crushing force (a proxy for shell strength; both metrics are known to increase in response to exudates from crab predators), and amino acid content. Amino acid content indicates the quantity and type of organic material present in shells and informs our understanding of the physiological mechanism of defense in oysters. Oysters exposed to blue crab exudates grew stronger shells containing less percent organic material than oysters in controls. In oysters collected from natural populations (spring 2014 and 2017; 28°N, 97°W), we tested the correlation between shell density and shell thickness to determine natural patterns of oyster shell morphology. We also performed regression analyses of soft tissue mass and gonad investment (gonad index, calculated as gonad tissue mass/soft tissue mass) to assess the relationship between shell morphology and other biologically valuable processes (growth and reproduction respectively). Shell density was negatively correlated with shell thickness, further suggesting oysters thicken their shells by increasing low-density calcium carbonate. Reproductive investment showed an increasingly negative relationship with thickness as density decreased (and induction increased). In a lab experiment (Texas A&M University-Corpus Christi; summer 2013), oysters were exposed to a temporal gradient in risk and tested for shell weight and strength to indirectly test hypotheses regarding the mechanism and costs of oyster defenses suggested by the above experiments. Oysters grew heavier shells in all crab treatments, but only grew stronger shells under constant exposure. Collectively, these results suggest oysters initially react to predators by adding inexpensive calcium carbonate to their shells to quickly outgrow risk. However, in high risk environments, oysters may increase production of costly organic material to increase shell strength. Thus, oysters demonstrate a two-tier mechanism allowing them to cheaply escape predation at lower risk but to build stronger shells at greater expense when warranted. These results illuminate the complex strategies prey deploy to balance predation risk and defense costs and the importance of understanding these strategies to accurately predict predator effects.

Description: Rising atmospheric CO2 concentrations threaten coral reefs globally by causing ocean acidification (OA) and warming. Yet, the combined effects of elevated pCO2 and temperature on coral physiology and resilience remain poorly understood. While coral calcification and energy reserves are important health indicators, no studies to date have measured energy reserve pools (i.e., lipid, protein, and carbohydrate) together with calcification under OA conditions under different temperature scenarios. Four coral species, Acropora millepora, Montipora monasteriata, Pocillopora damicornis, Turbinaria reniformis, were reared under a total of six conditions for 3.5 weeks, representing three pCO2 levels (382, 607, 741 µatm), and two temperature regimes (26.5, 29.0°C) within each pCO2 level. After one month under experimental conditions, only A. millepora decreased calcification (-53%) in response to seawater pCO2 expected by the end of this century, whereas the other three species maintained calcification rates even when both pCO2 and temperature were elevated. Coral energy reserves showed mixed responses to elevated pCO2 and temperature, and were either unaffected or displayed nonlinear responses with both the lowest and highest concentrations often observed at the mid-pCO2 level of 607 µatm. Biweekly feeding may have helped corals maintain calcification rates and energy reserves under these conditions. Temperature often modulated the response of many aspects of coral physiology to OA, and both mitigated and worsened pCO2 effects. This demonstrates for the first time that coral energy reserves are generally not metabolized to sustain calcification under OA, which has important implications for coral health and bleaching resilience in a high-CO2 world. Overall, these findings suggest that some corals could be more resistant to simultaneously warming and acidifying oceans than previously expected.

Description: The physiological response to individual and combined stressors of elevated temperature and pCO2 were measured over a 24-day period in four Pacific corals and their respective symbionts (Acropora millepora/Symbiodinium C21a, Pocillopora damicornis/Symbiodinium C1c-d-t, Montipora monasteriata/Symbiodinium C15, and Turbinaria reniformis/Symbiodinium trenchii). Multivariate analyses indicated that elevated temperature played a greater role in altering physiological response, with the greatest degree of change occurring within M. monasteriata and T. reniformis. Algal cellular volume, protein, and lipid content all increased for M. monasteriata. Likewise, S. trenchii volume and protein content in T. reniformis also increased with temperature. Despite decreases in maximal photochemical efficiency, few changes in biochemical composition (i.e. lipids, proteins, and carbohydrates) or cellular volume occurred at high temperature in the two thermally sensitive symbionts C21a and C1c-d-t. Intracellular carbonic anhydrase transcript abundance increased with temperature in A. millepora but not in P. damicornis, possibly reflecting differences in host mitigated carbon supply during thermal stress. Importantly, our results show that the host and symbiont response to climate change differs considerably across species and that greater physiological plasticity in response to elevated temperature may be an important strategy distinguishing thermally tolerant vs. thermally sensitive species.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in WHOI Fennel, K., Alin, S., Barbero, L., Evans, W., Bourgeois, T., Cooley, S., Dunne, J., Feely, R. A., Martin Hernandez-Ayon, J., Hu, X., Lohrenz, S., Muller-Karger, F., Najjar, R., Robbins, L., Shadwick, E., Siedlecki, S., Steiner, N., Sutton, A., Turk, D., Vlahos, P., & Wang, Z. A. Carbon cycling in the north american coastal ocean: A synthesis. Biogeosciences, 16(6), (2019):1281-1304, doi:10.5194/bg-16-1281-2019.

Description: A quantification of carbon fluxes in the coastal ocean and across its boundaries with the atmosphere, land, and the open ocean is important for assessing the current state and projecting future trends in ocean carbon uptake and coastal ocean acidification, but this is currently a missing component of global carbon budgeting. This synthesis reviews recent progress in characterizing these carbon fluxes for the North American coastal ocean. Several observing networks and high-resolution regional models are now available. Recent efforts have focused primarily on quantifying the net air–sea exchange of carbon dioxide (CO2). Some studies have estimated other key fluxes, such as the exchange of organic and inorganic carbon between shelves and the open ocean. Available estimates of air–sea CO2 flux, informed by more than a decade of observations, indicate that the North American Exclusive Economic Zone (EEZ) acts as a sink of 160±80 Tg C yr−1, although this flux is not well constrained. The Arctic and sub-Arctic, mid-latitude Atlantic, and mid-latitude Pacific portions of the EEZ account for 104, 62, and −3.7 Tg C yr−1, respectively, while making up 51 %, 25 %, and 24 % of the total area, respectively. Combining the net uptake of 160±80 Tg C yr−1 with an estimated carbon input from land of 106±30 Tg C yr−1 minus an estimated burial of 65±55 Tg C yr−1 and an estimated accumulation of dissolved carbon in EEZ waters of 50±25 Tg C yr−1 implies a carbon export of 151±105 Tg C yr−1 to the open ocean. The increasing concentration of inorganic carbon in coastal and open-ocean waters leads to ocean acidification. As a result, conditions favoring the dissolution of calcium carbonate occur regularly in subsurface coastal waters in the Arctic, which are naturally prone to low pH, and the North Pacific, where upwelling of deep, carbon-rich waters has intensified. Expanded monitoring and extension of existing model capabilities are required to provide more reliable coastal carbon budgets, projections of future states of the coastal ocean, and quantification of anthropogenic carbon contributions.

Description: This paper builds on synthesis activities carried out for the second State of the Carbon Cycle Report (SOCCR2). We would like to thank Gyami Shrestha, Nancy Cavallero, Melanie Mayes, Holly Haun, Marjy Friedrichs, Laura Lorenzoni, and Erica Ombres for the guidance and input. We are grateful to Nicolas Gruber and Christophe Rabouille for their constructive and helpful reviews of the paper. It is a contribution to the Marine Biodiversity Observation Network (MBON), the Integrated Marine Biosphere Research (IMBeR) project, the International Ocean Carbon Coordination Project (IOCCP), and the Cooperative Institute of the University of Miami and the National Oceanic and Atmospheric Administration (CIMAS) under cooperative agreement NA10OAR4320143. Katja Fennel was funded by the NSERC Discovery program. Steven Lohrenz was funded by NASA grant NNX14AO73G. Ray Najjar was funded by NASA grant NNX14AM37G. Frank Muller-Karger was funded through NASA grant NNX14AP62A. This is Pacific Marine Environmental Laboratory contribution number 4837 and Lamont-Doherty Earth Observatory contribution number 8284. Simone Alin and Richard A. Feely also thank Libby Jewett and Dwight Gledhill of the NOAA Ocean Acidification Program for their support.