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While the number of kelp farms have steadily increased, few have been deployed with sensors to measure mooring tensions with substantial biomass. During the kelp farming season of 2018–2019 in Saco Bay, Maine USA, a field study was conducted to assess mooring loads due to environmental conditions and kelp growth. The effort included the deployment of a farm with a 122 m cultivation line and spread mooring with rope, chain, and anchors in 15.2 m of water. The system was deployed with seeded twine in late November and harvested in May. In April, with kelp biomass estimated at 7.8 kg m−1, two load cells were installed to measure mooring tensions in response to currents and waves. The currents and waves were measured with two Acoustic Doppler Current Profilers deployed adjacent to the load cells. From these measurements, we characterized the maximum loading case in response to a complex hydrodynamic environment. The maximum tension occurred on the landward side of the farm even though wave exposure was seaward. The tension in the landward side mooring was dominated by steady drag from the currents going to the east southeast. During this event, the two profilers were positioned on the leading and trailing edges of the farm relative to the prevailing current direction. Velocities measured at 0.5 m bins showed a 26.7% reduction at the depths where the kelp was located. To analyze the dynamic portion of the load cell datasets, the oscillatory components were processed into energy density spectra. Results showed that mooring tensions were not affected by waves at frequencies greater than 0.175 Hz, with most of the energy occurring near 0.12 Hz. The tension spectra did reveal energy at frequencies between 0.0075 and 0.01 Hz, indicating a low frequency response, possibly due to nonuniform velocity profiles inducing vertical motion of the cultivation line. It was also observed that the landward mooring, subjected to higher currents, was more sensitive to oscillating loads than the slack seaward side. The high-fidelity dataset will be useful for numerical modeling validation to further understand these dynamics and to optimize kelp farm designs.

To keep global surface warming below 1.5°C by 2100, the portfolio of cost-effective CDR technologies must expand. To evaluate the potential of macroalgae CDR, we developed a kelp aquaculture bio-techno-economic model in which large quantities of kelp would be farmed at an offshore site, transported to a deep water “sink site”, and then deposited below the sequestration horizon (1,000 m). We estimated the costs and associated emissions of nursery production, permitting, farm construction, ocean cultivation, biomass transport, and Monitoring, Reporting, and Verification (MRV) for a 1,000 acre (405 ha) “baseline” project located in the Gulf of Maine, USA. The baseline kelp CDR model applies current systems of kelp cultivation to deep water (100 m) exposed sites using best available modeling methods. We calculated the levelized unit costs of CO2eq sequestration (LCOC; $ tCO2eq-1). Under baseline assumptions, LCOC was $17,048 tCO2eq-1. Despite annually sequestering 628 tCO2eq within kelp biomass at the sink site, the project was only able to net 244 C credits (tCO2eq) each year, a true sequestration “additionality” rate (AR) of 39% (i.e., the ratio of net C credits produced to gross C sequestered within kelp biomass). As a result of optimizing 18 key parameters for which we identified a range within the literature, LCOC fell to $1,257 tCO2eq-1 and AR increased to 91%, demonstrating that substantial cost reductions could be achieved through process improvement and decarbonization of production supply chains. Kelp CDR may be limited by high production costs and energy intensive operations, as well as MRV uncertainty. To resolve these challenges, R&D must (1) de-risk farm designs that maximize lease space, (2) automate the seeding and harvest processes, (3) leverage selective breeding to increase yields, (4) assess the cost-benefit of gametophyte nursery culture as both a platform for selective breeding and driver of operating cost reductions, (5) decarbonize equipment supply chains, energy usage, and ocean cultivation by sourcing electricity from renewables and employing low GHG impact materials with long lifespans, and (6) develop low-cost and accurate MRV techniques for ocean-based CDR.

In the Northeast USA, the aquaculture of macroalgae is a rapidly growing industry. Within this region, there are no established regulations for farm siting or methods of pathogen detection on macroalgae cultivated or harvested for human consumption. Bacterial pathogens from natural and anthropogenic sources may persist in coastal waters and can potentially contaminate macroalgae. During the winter growing season, sugar kelp Saccharina latissima and adjacent water were sampled from three sites of kelp aquaculture located in adjacent bays of ME, USA. Membrane filtration onto selective media detected Escherichia coli, Vibrio parahaemolyticus, and Vibrio alginolyticus in kelp and water samples at all sites, however plate counts were very low. The foodborne pathogens Salmonella enterica ser. Typhimurium, V. parahaemolyticus, and enterohemorrhagic E. coli O157:H7 were detected on enriched kelp samples from 83%, 78%, and 56% of sampling events, respectively, using molecular methods. Even with low bacterial levels, this frequency of detection confirms the risk of foodborne pathogens present on kelp and recommends the development of best management practices to control microbial growth during kelp harvest and processing. Bacterial plate counts from kelp samples often varied from those of water, indicating the importance of sampling the kelp directly, and that the association between bacterial pathogens on kelp and in the surrounding water should be further investigated. This study provides the first food safety assessment of sea vegetables in this region with the goal of providing data to enable the expansion of its industry.

Aquaculture of the blue mussel Mytilus edulis in the Gulf of Maine is a growing industry at a time when wild mussel populations are threatened by a rapidly changing ocean. Intertidal mussel beds have largely disappeared in the region raising concerns over the long-term viability of mussel farming. Histology and lipid fatty acid analysis were used to assess gametogenesis, energy investment, and pathology of farmed mussels collected twice monthly for three years in Casco Bay, ME. Energy investment in reproduction and storage differed significantly between years, suggesting interannual variability. Wet weight of fatty acids such as DHA and EPA corresponded to pre-spawning periods, when gonad tissue was most abundant. Overall, pathology assessment showed low levels of common pathogens, parasites, and cellular abnormalities. The survey did, however, reveal high levels of oocyte atresia, a probable indicator of physiological or environmental stress from unfavorable spawning conditions. In addition, the presence of the potentially damaging digenetic trematode Proctoeces maculatus was documented using histology, marking the northernmost detection in the Northwest Atlantic and a likely climate-driven range expansion. These trends may signal a challenging future for blue mussels in the Gulf of Maine. Forward-looking farm mitigation practices informed by these results should be developed to ensure future sustainability of this industry.

Variability in life history traits and structural diversity of commercially exploited fishes in response to stress can impact their population dynamics and sustainability. Using data from a fishery dependent sampling program from 1978 to 2011, we evaluated temporal variability of size and growth of adult Atlantic herring (Clupea harengus) in the Gulf of Maine. We then developed and tested the hypotheses on the links of such temporal changes to population density and environmental factors and found decreases in size and growth potential. Generalized additive models found that density dependence was the main driver of such changes over sea surface temperature and salinity. Our results highlight the importance of density dependent processes in regulating growth and population size structure for Atlantic herring in the Gulf of Maine.

Siderastrea siderea is one of the most abundant corals at high latitude shallow sites along the Florida Reef Tract (25°–27°N). This species is able to tolerate wide seawater temperature fluctuations and sedimentation stress, but its reproductive status at high latitudes and under marginal environmental conditions is poorly understood. The objectives of this study were to evaluate the reproductive potential of S. siderea along a latitudinal gradient (25°–27°N) and to determine if sexual maturity occurs in small (

Hydrodynamic characteristics are needed to optimize the design of kelp aquaculture systems. To support this need, the objective of this study was to resolve both the normal and tangential drag forces acting on a dense aggregate of kelp blades using full-scale physical model tests. The physical model was designed to match the exposed length, individual blade flexural rigidity, the number of blades per unit width, the mass/length of biomass, and the aggregate mass density of kelp cultured at the University of New England experimental aquaculture lease site in Saco Bay, Maine USA. Tow tests were conducted at the United States Naval Academy in a tank with the dimensions of 116m × 7.9m × 4.9 m. The large tank size enabled the use of the full-scale physical model, minimizing dynamic similarity issues. In a series of tests, the model was towed in orientations both aligned and perpendicular to the tow direction. Horizontal and vertical reaction forces were measured for five tow speeds, along with the deflection of the dense kelp aggregate. With these datasets and the wet weight biomass per length of the model, normal and tangential drag forces were calculated. Drag components were processed into corresponding normal and tangential drag-area values. The drag-area representation was chosen since reference areas were ambiguous for both the actual kelp and model. At the higher speeds, the total horizontal drag in the aligned configuration were slightly lower than for the perpendicular orientation. Normal drag-areas as a function of tow speed ranged from 2.36 m2/m to 1.39 m2/m for the aligned case and from 2.49 to 1.88 m2/m for the perpendicular case. Tangential drag-areas as a function of tow speed ranged from 0.264 m2/m to 0.0325 m2/m for the aligned case and from 0.213 to 0.0415 m2/m for the perpendicular case. A transition from a bluff body to a streamlined body occurred as the tow speeds increased. To investigate this transition, horizontal components of the normal and tangential drag forces were reconstructed with the results of the tow tests. The reconstructed forces were obtained using a force balance system of equations with drag-area values for tow speeds less than 0.25 m/s extrapolated from the experimental datasets. For both aligned and perpendicular orientations, the model-aggregate reconfigured at a threshold of 0.25 m/s. We defined the threshold for reconfiguration as the tow speed at which the horizontal component of tangential drag equaled or exceeded the horizontal component of the normal drag. The drag-area results from this study can be incorporated into a dynamic fluid-structure interaction model representing kelp aggregates as a finite element beam prescribed with in-situ values of length, volume, mass density and flexural-rigidity of kelp material.

Bivalve aquaculture farms are an integral part of the surrounding coastal marine ecosystem and associated food webs. What is not well understood is how these anthropogenically manipulated, dense, single-species cultures influence species trophodynamics in the coastal ocean. Fouling macrofauna biodiversity, macroalgae biomass, sediment, and food web structure were studied at two blue mussel (Mytilus edulis) floating raft rope-culture aquaculture farm structures and two analogous floating dock structures without mussels in Casco Bay, Maine, USA during the summers of 2016 and 2017. Shannon Wiener diversity index of macrofauna was variable across structures compared depending on month. Macroalgae biomass was significantly higher on farm structures exclusively due to green macroalgae. There was no shift in food web structure determined by stable isotope analysis (δ13C and δ15N) and Layman metrics. This study is an initial step critical to assessing interactions of bivalve farms with coastal food webs.

Mercury (Hg) contamination testing was conducted on winter-caught male spiny dogfish (Squalus acanthias) in southern New England and results compared to available data on Hg concentrations for this species. A limited risk-reward assessment for EPA (eicosapentanoic acid) and DHA (docosahexanoic acid) lipid concentrations of spiny dogfish was completed in comparison with other commonly consumed marine fish. Mean Hg concentrations were 0.19 ppm (±0.30) wet weight. In comparison, mean Hg concentrations in S. acanthias varied geographically ranging from 0.05 ppm (Celtic Sea) to 2.07 ppm (Crete, Mediterranean Sea). A risk-reward assessment for Hg and DHA+EPA placed S. acanthias in both "low-risk, high-reward" and "high-risk, high-reward" categories for consumption dependent on locations of the catch. Our results are limited and are not intended as consumption advisories but serve to illustrate the need for making more nuanced, geo-specific, consumption guidance for spiny dogfish that is inclusive of seafood traceability and nutritional benefits.

In the Northwest Atlantic Ocean (NWAO), spiny dogfish ( Squalus acanthias ) is a promising commercial species following of collapse of traditional groundfish stocks. There are little available data assessing polychlorinated biphenyls (PCBs) in NWAO spiny dogfish. Here, six non-dioxin like PCB indicator congeners used in European Union regulations (EU NDL-PCB) were quantified via gas chromatography/mass spectrometry in 50 mature male spiny dogfish landed in southern New England. The average total concentration of EU NDL-PCBs was 58 ± 43 ng/g (mean ± 1 standard deviation). PCB values (corrected for co-elution) were below the 200 ng/g EU regulatory limit. Results provide first recent regional insight into the PCB content of spiny dogfish in the NWAO. However, our study offers only a snapshot of one particular dogfish population, and might not be representative for the whole NWAO. This study underscores the need for further testing in this species.