Jennie E. Rheuban

An Integrated Assessment Model for Helping the United States Sea Scallop (Placopecten magellanicus) Fishery Plan Ahead for Ocean Acidification and Warming

Ocean acidification, the progressive change in ocean chemistry caused by uptake of atmospheric CO2, is likely to affect some marine resources negatively, including shellfish. The Atlantic sea scallop (Placopecten magellanicus) supports one of the most economically important single-species commercial fisheries in the United States. Careful management appears to be the most powerful short-term factor affecting scallop populations, but in the coming decades scallops will be increasingly influenced by global environmental changes such as ocean warming and ocean acidification. In this paper, we describe an integrated assessment model (IAM) that numerically simulates oceanographic, population dynamic, and socioeconomic relationships for the U.S. commercial sea scallop fishery. Our primary goal is to enrich resource management deliberations by offering both short- and long-term insight into the system and generating detailed policy-relevant information about the relative effects of ocean acidification, temperature rise, fishing pressure, and socioeconomic factors on the fishery using a simplified model system. Starting with relationships and data used now for sea scallop fishery management, the model adds socioeconomic decision making based on static economic theory and includes ocean biogeochemical change resulting from CO2 emissions. The model skillfully reproduces scallop population dynamics, market dynamics, and seawater carbonate chemistry since 2000. It indicates sea scallop harvests could decline substantially by 2050 under RCP 8.5 CO2 emissions and current harvest rules, assuming that ocean acidification affects P. magellanicus by decreasing recruitment and slowing growth, and that ocean warming increases growth. Future work will explore different economic and management scenarios and test how potential impacts of ocean acidification on other scallop biological parameters may influence the social-ecological system. Future empirical work on the effect of ocean acidification on sea scallops is also needed.

Using the Ocean Health Index to Identify Opportunities and Challenges to Improving Southern Ocean Ecosystem Health

The Antarctic coast and seas are considered some of the most pristine marine systems on Earth. Their comprehensive assessment is critical because meeting ambitious conservation objectives while maintaining sustainable human uses will be increasingly challenging with growing climate change impacts, recovery from past overharvesting, and potential revision of activities permitted with future revisions of the existing governance structure. We used the Ocean Health Index (OHI) to deliver an integrated assessment of the Antarctic marine ecosystems’ evolving ecological and social dimensions. The OHI provides a framework to evaluate sustainable delivery of benefits people want from healthy oceans by measuring progress towards 10 widely-held societal goals. These goals include, conservation objectives, as well as other objectives, so as to identify tradeoffs across multiple priorities. We adapted the Index to the unique aspects and data availability of Antarctica. OHI scores were calculated for each sub-region defined by the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) as well as the region overall. OHI scores for conservation-related goals (biodiversity, clean water) were generally high, though with some stressor impacts (i.e., climate-driven decline of sea-ice, and pathogen pollution). However, a sensitivity test on the sea-ice habitat indicator showed biodiversity scores might be much lower in the vicinity of the Antarctic Peninsula. Preservation of lasting special places, captured in the sense of place sub-goal, scored relatively low due to limited extent of Marine Protected Areas in the Southern Ocean. In several cases, scores are low due to under-utilization of resources, rather than environmentally unsustainable practices (e.g., food provision, natural products, tourism and recreation). However, increased human activities would intensify the risk of pollution, pathogen contamination, and disturbance to wildlife, particularly if compounded with future climate change impacts. Therefore, scores may reflect the need to select more conservative targets for human use, articulated in international treaties, taking future risks into account. Our results highlight the need for more research on both natural and social science aspects of the Antarctic system, as well as the need to evaluate targets under different scenarios, so as to provide robust science-based advice for future decision-making in the region.

Quantifying the Effects of Commercial Clam Aquaculture on C and N Cycling: an Integrated Ecosystem Approach

Increased interest in using bivalve cultivation to mitigate eutrophication requires a comprehensive understanding of the net carbon (C) and nitrogen (N) budgets associated with cultivation on an ecosystem scale. This study quantified C and N processes related to clam (Mercenaria mercenaria) aquaculture in a shallow coastal environment (Cherrystone Inlet, VA) where the industry has rapidly increased. Clam physiological rates were compared with basin-wide ecosystem fluxes including primary production, benthic nutrient regeneration, and respiration. Although clam beds occupy only 3xa0% of the ecosystem’s surface area, clams filtered 7–44xa0% of the system’s volume daily, consumed an annual average of 103xa0% of the phytoplankton production, creating a large flux of particulate C and N to the sediments. Annually, N regenerated and C respired by clam and microbial metabolism in clam beds were ∼3- and ∼1.5-fold higher, respectively, than N and C removed through harvest. Due to the short water residence time, the low watershed load, and the close vicinity of clam beds to the mouth of Cherrystone Inlet, cultivated clams are likely subsidized by phytoplankton from the Chesapeake Bay. Consequently, much of the N released by mineralization associated with clam cultivation is “new” N as it would not be present in the system without bivalve facilitation. Macroalgae that are fueled by the enhanced N regeneration from clams represents a eutrophying process resulting from aquaculture. This synthesis demonstrates the importance of considering impacts of bivalve aquaculture in an ecosystem context especially relative to the potential of bivalves to remove nutrients and enhance C sinks.

Implications of future northwest Atlantic bottom temperatures on the American lobster (Homarus americanus) fishery

Sea surface temperatures of the northwest Atlantic have warmed dramatically over the last several decades, while benthic temperatures have increased at a slower pace. Here we analyze a subset of the CMIP5 global Earth system model ensemble using a statistical downscaling approach to determine potential future changes in benthic temperatures on the northwest Atlantic continental shelf and slope (<500 m). We put future changes in the context of possible impacts of ocean warming on the high-value, wild-caught American Lobster (Homarus americanus) fishery. Future bottom temperatures of the northwest Atlantic under a business-as-usual (RCP8.5) and a climate-policy (RCP4.5) scenario are projected to increase by 0–1.58C and 1.2–2.48C by 2050 and 0–1.98C and 2.3–4.38C by the end of the century for RCP4.5 and RCP8.5, respectively. H. americanus experiences thermal stress at temperatures above 208C, and projected increases in temperature is likely to result in changes in the distribution of optimal thermal egg hatching and settlement indicators. Inshore regions of southern New England, where H. americanus biomass and catch have been declining historically, will likely become inhospitable under either future scenario, while thermal egg hatching and settlement indicators will expand offshore and in the Gulf of Maine. These changes imply that members of the fishery based in southern New England may need to recapitalize to larger vessels to prepare for potential changes brought on by future climate warming. Results from the downscaling presented here can be useful in preparing for potential changes to other fisheries or in future climate vulnerability analyses.

Assessing the Impact of Local and Regional Influences on Nitrogen Loads to Buzzards Bay, MA

Nitrogen and chlorophyll-a concentrations in estuarine systems often correlate positively with increased nitrogen input. To determine the interactions between nitrogen load, physical drivers, and water quality indicators, we estimated nitrogen inputs to 28 estuaries within the Buzzards Bay, Massachusetts (USA) watershed from 1985-2013. Estimates were derived by combining parcel specific wastewater disposal, point source wastewater discharge, land use, and atmospheric nitrogen deposition data with a previously verified nitrogen loading model. Linear regression analysis was used to quantify temporal trends in individual data sets and characterize relationships between variables. The land-use data indicated that fractional coverage of impervious surfaces increased with time for all sub-watersheds at the expense of vegetation and agriculture land use classes, reflecting a growth in residential unit density. Nitrogen loads decreased with time for most watersheds on the western side of Buzzards Bay, reflecting decreased atmospheric nitrogen deposition combined with management efforts to mitigate wastewater pollution. For most of Buzzards Bay’s eastern watersheds increases in nitrogen sourced from wastewater, driven primarily by the development of homes with on-site wastewater disposal, resulted in overall nitrogen load increases. The relationship between nitrogen load and mean summer in situ chlorophyll a underwent a shift to more chlorophyll a per unit nitrogen input over time that was partially correlated to climatic variables such as increased precipitation and warming water column temperatures.

Thirty-Three Years of Ocean Benthic Warming Along the U.S. Northeast Continental Shelf and Slope: Patterns, Drivers, and Ecological Consequences

Abstract The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid‐Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin‐scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.

Projected impacts of future climate change, ocean acidification, and management on the US Atlantic sea scallop (Placopecten magellanicus) fishery

Ocean acidification has the potential to significantly impact both aquaculture and wild-caught mollusk fisheries around the world. In this work, we build upon a previously published integrated assessment model of the US Atlantic Sea Scallop (Placopecten magellanicus) fishery to determine the possible future of the fishery under a suite of climate, economic, biological, and management scenarios. We developed a 4x4x4x4 hypercube scenario framework that resulted in 256 possible combinations of future scenarios. The study highlights the potential impacts of ocean acidification and management for a subset of future climate scenarios, with a high CO2 emissions case (RCP8.5) and lower CO2 emissions and climate mitigation case (RCP4.5). Under RCP4.5 and the highest impact and management scenario, ocean acidification has the potential to reduce sea scallop biomass by approximately 13% by the end of century; however, the lesser impact scenarios cause very little change. Under RCP8.5, sea scallop biomass may decline by more than 50% by the end of century, leading to subsequent declines in industry landings and revenue. Management-set catch limits improve the outcomes of the fishery under both climate scenarios, and the addition of a 10% area closure increases future biomass by more than 25% under the highest ocean acidification impacts. However, increased management still does not stop the projected long-term decline of the fishery under ocean acidification scenarios. Given our incomplete understanding of acidification impacts on P. magellanicus, these declines, along with the high value of the industry, suggest population-level effects of acidification should be a clear research priority. Projections described in this manuscript illustrate both the potential impacts of ocean acidification under a business-as-usual and a moderately strong climate-policy scenario. We also illustrate the importance of fisheries management targets in improving the long-term outcome of the P. magellanicus fishery under potential global change.