Student and Early Career Scientist Webinar Series

Ocean Acidification and Warming Act Synergistically to Reduce Cardiac Performance and Increase Disease Susceptibility in Juvenile American Lobster

November 10, 2020 
Amalia Harrington, Maine Sea Grant, University of Maine

Increased greenhouse gas emissions have caused rapid ocean warming (OW) and reduced ocean pH via acidification (OA). Both stressors will likely impact marine crustaceans, but they are often examined in isolation. We conducted an environmental stressor experiment to understand how exposure to current summer conditions, OW only, OA only, or both acidification and warming (OAW) differentially influence the thermal physiology and immune response of juvenile American lobster, Homarus americanus. Following a 42-d exposure to these stressor treatments, cardiac performance was assessed during an acute thermal stress, and lobsters were subjected to a subsequent 21-d pathogen challenge with Aerococcus viridans var. homari, the causative agent of gaffkemia. Lobsters exposed to OAW had significantly lower Arrhenius Break Temperatures (ABT; indicator of thermal limits of capacity) when compared to lobsters from all other treatments, suggesting these stressors act synergistically to reduce physiological performance. Individuals from the OW only and OAW treatments also had significantly lower total hemocyte counts (THCs; indicator of immune response) and showed a reduced median time to death (by up to 5 d sooner) post A. viridans injection compared to lobsters exposed to current summer conditions. Moreover, nearly twice as many lobsters exposed to OAW lost at least one claw during the pathogen challenge compared to all other treatment groups, potentially increasing the risk of mortality due to secondary infection. Together, these results suggest that predicted end-century OAW will impact the physiology and immune response of juvenile H. americanus, potentially influencing successful recruitment to the fishery.

The Effects of Ocean Acidification and Parental Environment on Shell Formation in Larval Eastern Oysters

January 27, 2021
Elise McNally, Northeastern University

Ocean acidification (OA) threatens shellfish production because it reduces the availability of carbonate ions in seawater, which calcifying organisms use to build their shells or skeletons. Eastern oysters (Crassostrea virginica) are ecologically and economically important species that generally exhibit negative responses to OA. Larval oysters are particularly vulnerable because of rapid rates of calcification and increased exposure of crystal nucleation sites to seawater. Changes in shell growth and morphology could result in decreased larval survival and subsequently decreased recruitment. Most previous studies have assessed the impacts of OA on larvae with parents naïve to the effects of OA. However, the environment that parents experience during reproductive conditioning could play a role in determining larval responses to OA through non-genetic inheritance mechanisms. We examined the effects of parental exposure to OA on Eastern oyster larval shell growth, shell morphology, and survival. We produced larvae from control-exposed and OA-exposed parents. Larvae from each cross were grown under control and OA conditions for three days. Parental exposure to OA increased the resilience of oyster larvae grown under OA conditions. OA-exposed larvae with OA-exposed parents exhibited faster growth rates and larger shells than OA-exposed larvae with control-exposed parents. Parental OA exposure was not sufficient to offset the effects of OA on biomineralization or survival in this experiment. However, these results suggest that parental exposure to OA mitigates some of the negative impacts of OA on Eastern oyster larvae and that oysters have the capacity to acclimate to OA.

Understanding Net Ecosystem Metabolism and Carbonate Chemistry at Near Coral Reef Ecosystems Using Moored Autonomous pCO2 Systems: Lessons From Puerto Rico and Florida

February 25, 2021
Melissa Melendez, Ph.D., University of Hawai'i at Manoa

Time series from open ocean fixed stations have robustly documented secular changes in carbonate chemistry and long-term ocean acidification (OA) trends as a direct response to increases in atmospheric carbon dioxide (CO₂). However, few high-frequency coastal carbon time series are available in reef systems, where most affected tropical marine organisms reside. Seasonal variations in carbonate chemistry at Cheeca Rocks (CR), Florida, and La Parguera (LP), Puerto Rico, are presented based on 8 and 10 years of continuous, high-quality measurements, respectively. The autonomous carbonate chemistry and oxygen observations are used to examine a mass balance approach using a 1-D model to determine net rates of ecosystem calcification and production (NEC and NEP) from communities close (<5km) to the buoys. 

High-frequency carbonate system data for these two multi-year time series show different seasonal amplitudes, offering insight into differing local biogeochemical processes. The current metabolic status of LP and CR, based on our results, are net dissolutional and net heterotrophic on the annual cycle. Results show that the seasonal cycle of carbonate chemistry cannot be attributed to temperature dynamics but rather reflects the combined effects of ecosystem processes. Respiration, particularly in late summer and fall, appears to be an additional source of CO₂ to the systems and can make calcification more energetically demanding as well as increase dissolution rates during this time of the year. This work contributes high-quality observations of ecosystem response and water chemistry under unique natural conditions. High-frequency data provided by these and similar operational systems can be used to develop early warning capabilities needed to identify and predict ecological trophic fluctuations.

The Consequences of Ocean Warming and Acidification for the Atlantic Sea Scallop Fishery

March 8, 2021 
Lousie Cameron, Woods Hole Oceanographic Institution

The Northwest Atlantic shelf is expected to experience accelerated rates of ocean warming and acidification over the 21^st century. Atlantic sea scallops inhabit the Northwest Atlantic shelf from Cape Hatteras to the Gulf of Maine and support one of the most profitable fisheries in the United States. Scallops have large calcite shells that may be vulnerable to dissolution under future ocean acidification. Here, I will present the results from mesocosm studies and field surveys designed to investigate the effects of ocean acidification and warming on Atlantic sea scallop shell and meat properties. I will also discuss my ongoing work to develop a spatially explicit model that will predict sea scallop vulnerability to ocean acidification across their rotational management areas using historic carbonate chemistry data and industry-based cruises.  

Expanding OA Monitoring Capacity with Community Science

April 20, 2021
Jennie Rheuban, Woods Hole Sea Grant and Parker Gassett, Maine Sea Grant

Ocean and coastal acidification (OCA) present a unique set of sustainability challenges at the human-ecological interface. Extensive biogeochemical monitoring that can assess local acidification conditions, distinguish multiple drivers of changing carbonate chemistry, and ultimately inform local and regional response strategies is necessary for successful adaptation to OCA.However, the sampling frequency and cost-prohibitive scientific equipment needed to monitor OCA are barriers to implementing the widespread monitoring of dynamic coastal conditions. Here, we will demonstrate through a case study that existing community-based water monitoring initiatives can help to address these challenges and contribute to OCA science. This webinar will highlight the results from the community science monitoring effort, "Shell Day", which was a single day regional water monitoring event coordinating total alkalinity, salinity, and temperature observations collected by 59 organizations including 7 research institutions across the northeastern United States. We will also highlight sequential outreach, workshop based training, and coordinated activities led by NECAN which facilitated Shell Day, and we will discuss the importance of these steps for regional capacity building.

Read more about Shell Day 2019 here. 

Synoptic Assessment of Coastal Total Alkalinity Through Community Science, Rheuban et al. 

Community Science for Coastal ACidification Monitoring and Research, Gassett et al. (in review)

Multiple Linear Regression Models for Estimating Carbonate System Conditions and Exploring Driving Processes in the Northeast US

May 13, 2021
Presented by Kelly McGarry, University of Connecticut Avery Point

In the coastal ocean, carbonate system trends  are determined by the interaction between ocean acidification and local processes. Sporadic observations indicate that biological metabolism, river inputs, and variable water mass contributions are dominant local processes driving carbonate system variability in northeast US shelf waters. These processes that affect carbonate chemistry also impact the variability of other observed hydrographic variables like temperature, salinity, oxygen concentration, and nitrate concentration. Here, we developed multiparameter linear regression (MLR) models that represent the processes that drive carbonate system variability in the Mid-Atlantic Bight and Gulf of Maine using observations obtained on three hydrographic surveys in summers between 2007 and 2015. Empirical model equations reveal the observation-based relationships between carbonate parameters and basic hydrographic variables. Unlike other regions where empirical models have been developed, salinity appears in most of the equations. Temperature is the most important parameter for predicting ΩAR, while salinity and oxygen are most important for predicting pHT. The basic hydrographic variables explain over 98% of the variability in total alkalinity (TA), dissolved inorganic carbon (DIC), and aragonite saturation state (ΩAR) and 89% of the variability in pH on total scale (pHT) in the calibration data. The empirical models perform well in evaluation against an independent data set not used in calibration, estimating TA and DIC with R2 > 0.97, ΩAR with R2 > 0.92, and pHT with R2 > 0.81. We apply these empirical models to temperature and salinity projections from a dynamically downscaled regional ocean model for the Gulf of Maine driven by boundary conditions from three global earth system models and adjust the results for the anthropogenic increase in carbon dioxide. Although warming continues to partially mitigate acidification rates in the region, ΩAR is projected to decline below 1.5 everywhere in the GoME by 2050 under RCP 8.5.

Controls on Buffering and Coastal Acidification in a New England Estuary

June 3, 2021 
Presented by Chris Hunt, University of New Hampshire

Estuaries may be uniquely susceptible to the combined acidification pressures of atmospherically-driven ocean acidification, biologically-driven CO 2 inputs from the estuary itself, and terrestrially-derived freshwater inputs. This study utilized continuous measurements of total alkalinity (TA) and the partial pressure of carbon dioxide (pCO 2 ) from the mouth of Great Bay, a temperate northeastern US estuary, to examine the potential influences of endmember mixing and biogeochemical transformation upon estuary buffering capacity (β-H). Observations were collected hourly over 28 months representing all seasons between May 2016 and December 2019. Results indicated that endmember mixing explained most of the observed variability in TA and dissolved inorganic carbon (DIC), concentrations of which varied strongly with season. For much of the year, mixing dictated the relative proportions of salinity- normalized TA and DIC as well, but a fall season shift in these proportions indicated that aerobic respiration was observed, which would decrease β-H by decreasing TA and increasing DIC. However, fall was also the season of weakest statistical correspondence between salinity and both TA and DIC, as well as the overall highest salinity, TA and β-H. Potential biogeochemically-driven β-H decreases were overshadowed by increased buffering capacity supplied by coastal ocean water. A simple modeling exercise showed that mixing processes controlled most monthly change in TA and DIC, obscuring impacts from air-sea exchange or metabolic processes. Advective mixing contributions, more than biogeochemically-driven changes, are critical to observe when evaluating local estuarine and coastal ocean acidification.