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Local adaptation and phenotypic plasticity play key roles in mediating organisms' ability to respond to spatiotemporal variation in temperature. These two processes often act together to generate latitudinal or elevational clines in acute temperature tolerance. Phenotypic plasticity is also subject to local adaptation, with the expectation that populations inhabiting more variable environments should exhibit greater phenotypic plasticity of thermal tolerance. Here we examine the potential for local adaptation and developmental plasticity of thermal tolerance in the widespread invasive tunicate Botryllus schlosseri. By comparing five populations across a thermal gradient spanning 4.4° of latitude in the northwest Atlantic, we demonstrate that warmer populations south of the Gulf of Maine exhibit significantly increased (∼0.2 °C) post-larval temperature tolerance relative to the colder populations within it. We also show that B. schlosseri post-larvae possess a high degree of developmental plasticity for this trait, shifting their median temperature of survival (LT 50) upwards by as much as 0.18 °C per 1 °C increase in environmental temperature. Lastly, we found that populations vary in their degrees of developmental plasticity, with populations that experience more pronounced short-term temperature variability exhibiting greater developmental plasticity, suggesting the local adaptation of developmental plasticity. By comparing the thermal tolerance of populations across space and through time, we demonstrate how geography and developmental plasticity have shaped thermal tolerance in B. schlosseri. These results help inform our understanding of how species are able to adjust their thermal physiology in new environments, including those encountered during invasion and under increasingly novel climate conditions. • Heat tolerance of an invasive tunicate's post-larvae varies along a latitudinal gradient. • Post-larvae exhibit putatively adaptive developmental plasticity of heat tolerance. • Plasticity varied by population and by degree of environmental thermal variability. [ABSTRACT FROM AUTHOR]

Floating marine debris (FMD) is one of the world's most concerning issues due to its potential impact on biodiversity, communities, and ecosystem services. FMD transport and concentrations are driven by fronts, generated by oceanographic processes, and the accumulation of FMD has been reported in gyres, eddies, tidal fronts, salinity fronts, and coastal fronts. This study explores the relationship between fronts and FMD accumulation in the Gulf of Maine (GoM) and the surrounding coastal areas (USA). Frontal edge detection algorithms were applied to sea surface temperature (SST) imagery from the Moderate-resolution Imaging Spectroradiometer (MODIS) between 2002 and 2012. Frontal location is spatially correlated with FMD concentrations collected by the Sea Education Association. Higher concentrations of FMD are associated with frontal frequencies (FF) of 5–10 %. FMD is trapped between fronts and the coastline in accumulation zones. These results highlight the need to consider coastal FMD hotspots, given these are areas of high biodiversity value. • Three floating marine debris (FMD) accumulation zones in the Gulf of Maine (GoM) and coastal areas are identified. • FMD appear to be trapped between fronts and the coastline in the three accumulation zones. • Higher FMD concentrations (1–5 × 103 pcs/km2) accumulate in high frontal frequency (FF) zones (5–10 %). • Lower FMD concentrations (<1000 pcs/km2) distribute in low FF zones (<5 %). [ABSTRACT FROM AUTHOR]

• An evaluation of eight global ocean reanalyses for the Northeast U.S. continental shelf. • Alma Carolina Castillo-Trujillo, Young-Oh Kwon, Paula Fratantoni, Ke Chen, Hyodae Seo, Michael A. Alexander, Vincent S. Saba. • The Northeast U.S. (NES) continental shelf is better represented in BRAN2020 and GLORYS12v1. • The reanalyses are mostly limited by the resolution, the representation of the Gulf Stream, and bathymetry. • Conditions in the Mid Atlantic Bight are represented less accurately than the rest of the NES. The Northeast U.S. continental Shelf (NES) extending from the Gulf of Maine to Cape Hatteras, is a dynamic region supporting some of the most commercially valuable fisheries in the world. This study aims to provide a systematic assessment of eight widely used, intermediate-to-high spatial resolution global ocean reanalysis products (CFSR, ECCO, ORAS, SODA, BRAN, GLORYS, GOFS3.0, and GOFS3.1) against available in situ and satellite ocean observations. In situ observations include water level from tide gauges, and temperature and salinity from various sources including shipboard hydrographic data, and moorings on the NES. Overall, the coarser resolution products exhibit limited skill in the coastal environment, with the high-resolution products better representing the temperature and salinity on the NES. Common biases are found in all reanalyses and in some regions within the NES; for example, biases in temperature and salinity are larger in the southern Mid-Atlantic Bight than in the rest of the NES. There is no single reanalysis that performs well across all parameters in all regions within the NES, but GLORYS and BRAN stand out for their superior performance across the largest number of metrics, outperforming other products in 22 and 25 of the 65 metrics examined, respectively. SODA is the top performer among the coarser resolution products (CFSR, ECCO, ORAS and SODA). The Gulf Stream and local bathymetry are critical factors leading to differences between the reanalyses. Conditions in summer are less well represented than in winter. In particular, the Mid-Atlantic Bight Cold Pool is not reproduced in four (CFSR, ECCO, ORAS, BRAN) of the eight reanalyses. [ABSTRACT FROM AUTHOR]

Introduced species can have profound impacts on communities by displacing and consuming native organisms. The intertidal communities in the Gulf of Maine have been radically altered through a suite of invasions in the early 1800s, including the herbivorous snail Littorina littorea and the omnivorous European green crab Carcinus maenas leading to morphological and distributional changes in two native gastropod grazers (Littorina saxatilis and Littorina obtusata). Green crabs and native cancrid crabs occupy the mid to low intertidal zones, leaving the high intertidal zones relatively free from crab predation pressure. However, a more recent invasion in the 1980s by the intertidal omnivorous Asian shore crab Hemigrapsus sanguineus , has eliminated this predator-free zone in the high intertidal. This invasion is of particular concern to populations of L. saxatilis , which were relegated to the high intertidal through combined competition and predation pressure by L. littorea and C. maenas. In order to quantify the potential impact of H. sanguineus on native snails, we conducted both field and lab experiments, testing the susceptibility of different sized snails to predation by introduced crabs. Additionally, we measured the distribution, abundance, and morphology of intertidal snails and crabs. Smaller snails of all species were the most susceptible to predation, although susceptibility differed among snail species and predation capabilities differed among crab species. L. saxatilis was the most vulnerable snail species to predation, with 73 and 64% of the population susceptible to large H. sanguineus and small C. maenas , respectively, while >96% of the L. littorea population was resistant to predation. L. saxatilis has been relegated to the high intertidal where there is high abiotic stress and poor-quality food, but until the invasion of H. sanguineus , there was little predation risk. This added predation pressure may further threaten populations of L. sa x atilis, especially as the upper intertidal becomes more hostile with increasing temperatures and possible species introductions. • Crabs and snails had clear tidal height distributions that varied seasonally. • Introduced snails and crabs were the more abundant in surveys. • Small snails invested in shell length, while large snails shifted to shell thickening. • Introduced crabs consumed all littorinids, preferring the smallest size classes. • Littorina saxatilis was the most vulnerable of the snails to decapod predation. [ABSTRACT FROM AUTHOR]

Artificial environments have hard surfaces positioned at different orientations that attract a wide diversity of sessile invertebrate species, forming fouling communities. Fouling communities play a large role in the spread of a species introduction, as organisms gain purchase in artificial environments and use them as a stepping-stone into neighboring natural systems. These man-made systems harbor a large diversity of species, and there are often vastly different communities present on both vertical and horizontal surfaces. We used a species abundance dataset at three time periods spanning 30 years, collected from fouling panels in a high tidal flow estuary at the mouth of the Piscataqua River (New Castle, New Hampshire) in the southern Gulf of Maine to measure differences in community composition between horizontal and vertical panels. Early successional communities on settlement panels were photographed one year after installment in late summer to capture the highest diversity seasons. Organisms were then identified to the lowest taxonomic level, and communities on the underside of horizontal and vertical panels were compared. Vertical and horizontal communities from 1980 and 2004 were similar, while those from 2009 statistically differed from one another. Vertical and horizontal surfaces in the 1980s were dominated by the blue mussel Mytilus edulis , which declined in later years, and was replaced by invasive ascidians. Species diversity increased between the 1980 and 2004 sampling, but declined by the 2009 sampling. This study captures changes of species composition in early successional communities on vertical and horizontal surfaces at a single locale from three time periods spanning over 30 years. • Community composition significantly differed between horizontal and vertical panels in 2009 but not 1980 or 2004. • Communities within a single panel orientation became more homogeneous over time. • Longer lived species were significant indicators for panel communities. • Invasive tunicates dominated both panel orientations in 2004 and 2009. • Species diversity peaked in 2004. [ABSTRACT FROM AUTHOR]

Habitat use and distribution is a critical aspect in the management and conservation of a species, particularly for those in decline. Habitat suitability indices (HSI) are a common method of habitat mapping dependent on empirical data that can easily lead to misunderstanding the spatiotemporal dynamics of marine species experiencing population decline and density dependent catchability within surveys. This is especially true when only a single monitoring program with limited spatiotemporal coverage is used. A delta-generalized linear mixed model was used to combine trawl and longline surveys to predict density estimates for cusk (Brosme brosme) in unsampled locations for use in HSIs. Catchability was estimated for longline and trawl gear without having an estimate of area fished for the longline survey. HSIs performed better using model-based density estimates from multiple surveys compared with sample-based abundance indices from a single survey. The increased spatial resolution can better inform the HSIs by providing information where the survey programs did not sample. This study provides a novel approach for integrating data from different monitoring programs for habitat modeling. L'utilisation et la repartition des habitats sont des aspects d'importance cle pour la gestion et la conservation des especes, en particulier les especes en declin. Les indices de qualite de l'habitat (IQH) constituent une methode repandue de cartographie des habitats qui repose sur de donnees empiriques pouvant facilement mener a une comprehension erronee de la dynamique spatiotemporelle d'especes marines dont les populations sont en declin et de la capturabilite dependante de la densite dans les evaluations. Cela est particulierement vrai quand une seule campagne de surveillance de couverture spatiotemporelle limitee est utilisee. Un modele de melange lineaire generalise delta a ete utilise pour combiner des evaluations au chalut et a la palangre afin d'etablir des estimations prevues de la densite pour le brosme (Brosme brosme) dans des emplacements non echantillonnes pour utilisation dans des IQH. La capturabilite a ete estimee pour les palangres et les chaluts en l'absence d'estimation de la superficie pechee pour revaluation a la palangre. Les IQH donnent de meilleurs resultats quand des estimations de la densite modelisees basees sur plusieurs evaluations sont utilisees, comparativement a des indices d'abondance bases sur les echantillons tires d'une seule evaluation. La resolution spatiale accrue peut etre avantageuse pour la determination des IQH parce qu'elle fournit de l'information pour les emplacements non echantillonnes lors des campagnes devaluation. L'etude fournit une nouvelle approche d'integration de donnees de differentes compagnes de surveillance pour la modelisation des habitats. [Traduit par la Redaction], Introduction Habitat use and distribution is a critical aspect in the management and conservation of a species, particularly for those in decline. Habitat suitability indices (HSIs) are a method of [...]

Ecosystem-based fishery management requires understanding of relationships between exploited fish and their predators, such as seabirds. We used exploratory regression analyses to model relationships between Atlantic herring (Clupea harengus) in the diet of seabird chicks at nine nesting colonies in the Gulf of Maine and four types of fishery- and survey-derived herring data. We found several strong relationships, which suggests spatial structuring in herring stocks and likely patterns of herring movements before they recruit into the fishery. Some types of herring data seldom used in stock assessments--notably acoustic surveys, fixed-gear landings, and mass-at-age (i.e., weight-at-age)--correlated as strongly with seabird data as more commonly used series, such as mobile-gear landings and modeled spawning stock biomass. Seabird chick diets collected at specific locations thus offer a promising means to assess the size, distribution, and abundance of juvenile herring across a broad area prior to recruitment, which is a major source of uncertainty in fisheries. Common terns (Sterna hirundo) showed the most potential as a bioindicator, correlating well and showing consistent spatial patterns with 11 of 13 fishery data series. La gestion ecosystemique des peches necessite une comprehension des liens entre les poissons exploites et leurs predateurs, tels que les oiseaux marins. Nous avons utilise des analyses de regression exploratoires pour modeliser les relations entre le hareng de l'Atlantique (Clupea harengus) dans l'alimentation de jeunes oiseaux de mer dans neuf colonies de nidification dans le golfe du Maine, et quatre types de donnees sur les harengs issues de la peche et de campagnes devaluation. Nous avons releve plusieurs relations marquees qui indiqueraient la presence d'une structure spatiale dans les stocks de harengs et de probables motifs de deplacement des harengs avant leur recrutement dans la peche. Certains types de donnees sur les harengs rarement utilises dans les evaluations des stocks, dont des donnees de releves acoustiques, de debarquements de navires a engins fixes et de poids selon l'age, presentent une correlation tout aussi forte avec les donnees sur les oiseaux de mer que des series plus couramment utilisees, comme les debarquements de navires a engins mobiles et la biomasse modelisee du stock reproducteur. Les regimes alimentaires des jeunes oiseaux de mer preleves en des sites precis constituent donc une approche prometteuse pour evaluer la taille, la repartition et l'abondance des harengs juveniles avant leur recrutement a l'echelle d'une grande region, des facteurs qui constituent une importante source d'incertitude dans les peches. Les sternes pierregarins (Sterna hirundo) montrent le meilleur potentiel comme bioindicateur, puisqu'elles presentent une bonne correlation et des motifs spatiaux concordants avec 11 des 13 series de donnees issues de la peche. [Traduit par la Redaction], Introduction Fisheries managers worldwide are increasingly expected to oversee harvested stocks with due regard to their interactions with other species in the ecosystem (Stephenson 2012). Successful application of this approach, [...]

An anomalous winter phytoplankton bloom was observed across the central Gulf of Maine during a winter cruise in late February 1999, but not during a similar mission to the same region in late February 2000. During the cruise in 1999, 0 to 40 m mean chl a concentrations were >2 μg 1-1, while in 2000 total chl a concentrations were 5 pm size fractions were 10x more abundant in 1999 and included species typically not present in the central Gulf during winter. All developmental stages of planktonic copepods were present, including large numbers of older copepodid stages of species such as Calanus finmarchicus, indicating that the bloom had been proceeding for some time. RNA:DNA ratios of surface C. finmarchicus stage C5 and adult females were at or near maximum temperature-dependent values in 1999, but were considerably reduced in 2000. Egg production rates of C. finmarchicus were high in 1999 but reduced in 2000. Both showed a curvilinear relationship with chl a. Analysis of gonads of females of other copepod species indicate similar between-year differences in reproductive rates. We suggest that the presence of the winter bloom in the central Gulf of Maine allows an extra generation of C. finmarchicus and other copepods to develop, leading to a buildup of the population during winter. This will have significant effects on downstream regions such as Georges Bank, which depend on re-supply from the Gulf of Maine.

Atlantic halibut (Hippoglossus hippoglossus, Linnaeus, 1758) are a data-poor stock within the waters of the United States. This study evaluated the use of otolith measurements to back-calculate lengths of Atlantic halibut at previous ages. Back-calculations have proven useful for estimating length at age and growth rates of other species. To the best knowledge of the authors, this study is the first to document the use of this method for Atlantic halibut. Otolith back-calculations rely on a few key assumptions, such as proportionality of fish length and otolith length, which are not always met. This study shows that back-calculations using the Fraser-Lee method can provide reasonable estimates of Atlantic halibut length at previous ages, especially when samples from young halibut are included to improve estimates of the intercept of the linear regressions. Based on back-calculated estimates, female and male halibut in the Gulf of Maine showed different growth rates after age five. There was no evidence of changes in growth rates over an approximately 15 year time period. Halibut caught in the Gulf of Maine and on the neighboring Scotian Shelf showed some differences in growth rates; however, the results did not support strong conclusions about differences between the two regions as the direction of the differences was not consistent between the sexes and previous tagging studies have shown extensive movement between the two areas. The finding of reasonably accurate back-calculated lengths at previous ages is important for this data-poor species, as back-calculations increase the amount of information that can be obtained from otoliths.

Abstract Landscape patterns created by the structure and form of foundational species shape ecological processes of community assembly and trophic interactions. In recent years, major shifts in foundation species have occurred in multiple ecosystems. In temperate marine systems, many kelp beds have shifted to turf macroalgae habitats with unknown consequences on seascape patterns or changes in the ecological processes that maintain communities. We investigated the effect of turf macroalgae on seascape patterns in three habitats dominated by kelp and turf macroalgae and those that have mixed species composition. We also examined decadal elevations in temperature with known growth and reproductive phenology of kelp and turf macroalgae to provide a mechanistic understanding of the factors that will continue to shape these seascapes. Our results indicate that turf macroalgae produce a more heterogeneous habitat with greater primary free space than those that are mixed or dominated by kelp. Further, we examined the relationship between seascape patterns and richness and abundance of fishes in each habitat. Results showed that patch size was positively related to the abundance of fish in habitat types, suggesting that turf‐induced heterogeneity may lead to fewer observed fishes, specifically the mid‐trophic level species, cunner, in these habitats. Overall, our results suggest that persistence of this habitat is facilitated by increasing temperature that shorten the phenology of kelps and favor growth and reproduction of turf macroalgae that make them poised to take advantage of free space, regardless of season.

Abstract Distribution shifts poleward are a widespread response to climate change and can result in altered community composition and interactions among species that previously were geographically isolated. The novel communities and species interactions that may arise during range shifts provide an opportunity to study fundamental ecological processes, while also addressing potential conservation issues. Black sea bass (Centropristis striata) historically ranged from the Gulf of Mexico to Cape Cod, but recently have expanded north into the Gulf of Maine. Very little is known about the impact of this range expansion on benthic community structure throughout the coastal waters of the Gulf of Maine. To investigate the effects of sea bass on the behavior of juvenile American lobsters (Homarus americanus), we manipulated the presence of sea bass olfactory cues and quantified shelter use and foraging behavior of lobsters from three regions in the Gulf of Maine with different potential contact histories with sea bass. Sea bass presence increased shelter usage and reduced foraging in lobsters, but contact history influenced the strength of these behavioral responses. Lobsters with no previous contact with sea bass did not significantly increase shelter usage or decrease movement in their presence but did reduce their foraging rate on mussels. This observed reduction in consumption indicates that naïve lobsters recognize novel predators, but the ineffective anti‐predator responses exhibited support the naive prey hypothesis. Meanwhile, lobsters with the longest potential contact history with sea bass significantly increased shelter usage when sea bass were present; however, they exhibited limited movement and foraging behavior in both the absence and presence of sea bass. Finally, lobsters with a short potential contact history with sea bass exhibited increased shelter usage, reduced movement, and reduced mussel consumption in the presence of sea bass, revealing that juvenile lobsters quickly adapt anti‐predator defenses to avoid this novel threat. Overall, these results suggest that prey contact history with novel predators mediates the strength of their nonconsumptive effects, and consequently can influence geographic patterns in predator–prey dynamics.

The phenology of major seasonal events is an important indicator of climate. We analyzed multiple datasets of in situ chlorophyll measurements from the Gulf of Maine dating back to the early 20th century in order to detect climate-scale changes in phenology. The seasonal cycle was consistently characterized by a two-bloom pattern, with spring and autumn blooms. The timing of both spring and autumn blooms has shifted later in the year at rates ranging from ∼1 to 9 days per decade since 1960, depending on the phenology metric, and trends only emerged at time scales of >40 years. Bloom phenology had only weak correlations with major climate indices. There were stronger associations between bloom timing and physical and chemical variables. Autumn bloom initiation correlated strongly with surface temperature and salinity, and spring bloom with nutrients. A later spring bloom also correlated with an increased cohort of Calanus finmarchicus, suggesting broader ecosystem implications of phytoplankton phenology.

Most marine crustacean eggs contain the full complement of nutritional resources required to fuel their growth and development. Given the propensity of many ovigerous (egg-bearing) American lobsters (Homarus americanus) to undergo seasonal inshore-to-offshore migrations, thereby potentially exposing their eggs to varying thermal regimes, the goal of this study was to determine the impact of water temperature on egg quality over their course of development. This was accomplished by documenting changes in total lipids, proteins, and size (volume) of eggs subjected to one of three thermal regimes: inshore, offshore, and constant (16 °C) conditions. Total egg lipids showed a marked decrease over time, while protein levels increased over the same period. Although there were no significant differences in total lipids, proteins, or egg sizes between eggs exposed to inshore and offshore temperatures, they differed from values for eggs exposed to a constant temperature, which also hatched almost three months sooner. This is most likely due to the fact that eggs held at a constant temperature did not experience a period of slow development during the colder months from November to March that are important for synchronizing egg hatch and may be compromised by elevated seawater temperatures.

A significant amount of organic carbon is transported in dissolved form from soils to coastal oceans via inland water systems, bridging land and ocean carbon reservoirs. However, it has been discovered that the presence of terrigenous dissolved organic carbon (tDOC) in oceans is relatively limited. Therefore, understanding the fates of tDOC in coastal oceans is essential to account for carbon sequestration through land ecosystems and ensure accurate regional carbon budgeting. In this study, we developed a state-of-the-art modeling approach by coupling a land-to-ocean tDOC flux simulation model and a coastal tDOC tracking model to determine the potential fates of tDOC exported from three primary drainage basins in the Gulf of Maine (GoM). According to our findings, over half a year in the GoM, 56.4% of tDOC was mineralized. Biomineralization was responsible for 90% of that amount, with the remainder attributed to photomineralization. Additionally, 37% of the tDOC remained suspended in the GoM, and 6.6% was buried in the marine sediment.

The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica , with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13C carbonate) and oxygen (δ18O carbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to "unexpected" variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation = 0.65‰), approximately four times more variable than analytical precision. High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series. • Isotope replication of carefully sampled, contemporaneously produced material was within analytical uncertainty • Seasonal heterogeneity in isotopic composition is likely primary cause of variability in annually replicated material • Uncertainty in isotopic measurements is substantially reduced when data are replicated using at least four shells • Study-specific replication and error propagation are highly encouraged for all paleoclimate studies using isotope proxies [ABSTRACT FROM AUTHOR]

Ocean warming can drive poleward shifts of commercially important species with potentially significant economic impacts. Nowhere are those impacts greater than in the Gulf of Maine where North America's most valuable marine species, the American lobster (Homarus americanus Milne Edwards), has thrived for decades. However, there are growing concerns that regional maritime economies will suffer as monitored shallow water young‐of‐year lobsters decline and landings shift to the northeast. We examine how the interplay of ocean warming, tidal mixing, and larval behavior results in a brighter side of climate change. Since the 1980s lobster stocks have increased fivefold. We suggest that this increase resulted from a complex interplay between lobster larvae settlement behavior, climate change, and local oceanographic conditions. Specifically, postlarval sounding behavior is confined to a thermal envelope above 12°C and below 20°C. Summer thermally stratified surface waters in southwestern regions have historically been well within the settlement thermal envelope. Although surface layers are warming fastest in this region, the steep depth‐wise temperature gradient caused thermally suitable areas for larval settlement to expand only modestly. This contrasts with the northeast where strong tidal mixing prevents thermal stratification and recent ocean warming has made an expansive area of seabed more favorable for larval settlement. Recent declines in lobster settlement densities observed at shallow monitoring sites correlate with the expanded area of thermally suitable habitat associated with warmer summers. This leads us to hypothesize that the expanded area of suitable habitat may help explain strong lobster population increases in this region over the last decade and offset potential future declines. It also suggests that the fate of fisheries in a changing climate requires understanding local interaction between life stage‐specific biological thresholds and finer scale oceanographic processes. [ABSTRACT FROM AUTHOR]

Discriminating among sympatric sub-populations is critical not only for the investigation of fish population structure, but also for effective fishery management. The Gulf of Maine stock of Atlantic cod contains two genetically distinct sub-populations whose spawning grounds overlap in space, but not season. Lack of a practical tool for discriminating between these spring and winter spawners has thus far prevented addressing metapopulation structure in stock assessments and fishery management plans. To address this issue, we developed a simple approach to discriminate between the sympatric sub-populations that relies on internal otolith structures. Using a logistic regression model fit to training data (n = 577) and evaluated through cross-validation, we correctly classified individuals with 81% accuracy and predicted the overall sub-population mixture within 1%. Applying the model to a broader population dataset (n = 1642) revealed that spring-spawned cod are more concentrated within closed fishing areas and therefore experience a lower mortality rate. However, despite dominating older age classes and comprising a large fraction of the spawning stock, these spring cod contribute little to recruitment. This apparent sub-population difference in the stock–recruitment relationship has important consequences for assessment models and the success of management measures designed to rebuild the stock. [ABSTRACT FROM AUTHOR]

Effective fishery management measures to protect fish spawning aggregations require reliable information on the spatio-temporal distribution of spawning. Spawning closures have been part of a suite of fishery management actions to rebuild the Gulf of Maine stock of Atlantic cod (Gadus morhua), but difficulties remain with managing rebuilding. The objective of this study was to identify the spatial and temporal distribution of cod spawning during winter in Massachusetts Bay to improve our understanding of cod spawning dynamics and inform fisheries management. Spawning was investigated in collaboration with commercial fishermen during three winter spawning seasons (October 2013–March 2016) using acoustic telemetry and passive acoustic monitoring equipment deployed in fixed-station arrays and mounted on mobile autonomous gliders. Tagged cod exhibited spawning site fidelity and spawning primarily occurred from early November through January with a mid-December peak and some inter-annual variability. The spatial distribution of spawning was generally consistent among years with multiple hotspots in areas >50 m depth. Current closures encompass most of spawning, but important areas are recommended for potential modifications. Utilizing multiple complementary technologies and deployment strategies in collaboration with commercial fishermen enabled a comprehensive description of spawning and provides a valuable model for future studies. [ABSTRACT FROM AUTHOR]

Climate‐driven warming has both social and ecological effects on marine fisheries. While recent changes due to anthropogenic global warming have been documented, similar basin‐wide changes have occurred in the past due to natural temperature fluctuations. Here, we document the effects of rapidly changing water temperatures along the United States' east coast using observations from fisheries newspapers during a warming phase (1945–1951) and subsequent cooling phase (1952–1960) of the Atlantic Multidecadal Oscillation, which we compared to similar recent observations of warming waters (1998–2017). Historical warming and cooling events affected the abundance of species targeted by fishing, the prevalence of novel and invasive species, and physical access to targeted species. Fishing communities viewed historical cooling waters twice as negatively as they did warming waters (72% vs. 35% of observations). Colder waters were associated with a decrease in fishing opportunity due to storminess, while warming waters were associated with the potential for new fisheries. In contrast, recent warming waters were viewed as strongly negative by fishing communities (72% of observations), associated with disease, reductions in abundances of target species, and shifts in distributions across jurisdictional lines. This increasing perception that warming negatively affects local fisheries may be due to an overall reduction of opportunity in fisheries over the past half century, an awareness of the relative severity of warming today, larger changes in American culture, or a combination of these factors. Negative perceptions of recent warming waters' effects on fisheries suggest that fishing communities are currently finding the prospect of climate adaptation difficult. [ABSTRACT FROM AUTHOR]

Landscape patterns created by the structure and form of foundational species shape ecological processes of community assembly and trophic interactions. In recent years, major shifts in foundation species have occurred in multiple ecosystems. In temperate marine systems, many kelp beds have shifted to turf macroalgae habitats with unknown consequences on seascape patterns or changes in the ecological processes that maintain communities. We investigated the effect of turf macroalgae on seascape patterns in three habitats dominated by kelp and turf macroalgae and those that have mixed species composition. We also examined decadal elevations in temperature with known growth and reproductive phenology of kelp and turf macroalgae to provide a mechanistic understanding of the factors that will continue to shape these seascapes. Our results indicate that turf macroalgae produce a more heterogeneous habitat with greater primary free space than those that are mixed or dominated by kelp. Further, we examined the relationship between seascape patterns and richness and abundance of fishes in each habitat. Results showed that patch size was positively related to the abundance of fish in habitat types, suggesting that turf-induced heterogeneity may lead to fewer observed fishes, specifically the mid-trophic level species, cunner, in these habitats. Overall, our results suggest that persistence of this habitat is facilitated by increasing temperature that shorten the phenology of kelps and favor growth and reproduction of turf macroalgae that make them poised to take advantage of free space, regardless of season. [ABSTRACT FROM AUTHOR]

Estimation of abundance or biomass, using acoustic techniques requires knowledge of the frequency dependent acoustic backscatter characteristics, or target strength, of organisms. Target strength of zooplankton is typically estimated from physics‐based models that involve multiple parameters, notably including the acoustic material properties (i.e., the contrasts in density and sound speed between the animal and surrounding seawater). In this work, variability in the acoustic material properties of two zooplankton species in the Gulf of Maine, the copepod (Calanus finmarchicus) and krill (Meganyctiphanes norvegica), was investigated relative to changing season as well as, for the copepod, temperature and depth. Increases in the density and sound speed contrasts of these species from fall to spring were observed. Target strength predictions based on these measurements varied between fall and spring by 2‐3 dB in krill. Measurements were also conducted on C. finmarchicus lipid extract at changing temperature and pressure. The density contrast of the extract varied negatively with temperature, while the sound speed contrast changed by more than 10 % over the temperature and pressure ranges that the organism expected to occupy. C. finmarchicus target strength predictions showed that the combined effect of temperature and pressure can be significant (more than 10 dB) due to the varying response of lipids. The large vertical migration ranges and lipid accumulation characteristics of these species (e.g., the diapause behaviour of Calanus copepods) suggest that it is necessary for seasonal and environmental variability in material properties to be taken into account to achieve reliable measurements. [ABSTRACT FROM AUTHOR]

Atlantic menhaden (Brevoortia tyrannus) is a migratory forage fish whose geographic range extends from the Gulf of Maine to Florida. Despite the ecological and commercial importance of menhaden, few fishery-independent surveys have been conducted to quantify their distributions of abundance and biomass. Active acoustic surveys of menhaden schools were conducted using 38, 120, and 200 kHz scientific echosounders in two regions on the continental shelf south of Long Island, New York during the summer of 2014 and spring, summer, and fall of 2015. Spatial distributions of menhaden schools were considered to be clustered across all surveys where three or more schools were observed. Estimates of school volume were highly variable, ranging from 30 to 48,000 m3. Menhaden aggregations were absent in the spring (April, May, and June) and present in the summer and fall (July, August, and September) surveys. Target strength measurements at 120 kHz during the summer and fall surveys were consistent with predicted values for adult Atlantic menhaden, suggesting that fish size did not change substantially during this time. Peak menhaden abundance was observed during August 2015 (approximately 157,000 fish km−2 with a wet weight biomass density of 35,000 kg km−2). Multifrequency acoustic surveys can provide an efficient and fishery-independent method for quantifying menhaden abundance and distribution in coastal habitats. [ABSTRACT FROM AUTHOR]

Individual-based models (IBMs) can capture complex processes with a flexible probabilistic approach, which makes them useful for studying organisms with complex life history and fishery processes such as the American lobster (Homarus americanus). This research aims to modify and parameterize an individual-based lobster simulator (IBLS) to simulate the American lobster fishery in the Gulf of Maine. To simulate the fishery, the IBLS was tuned to match the seasonal catch and size composition from the 2015 American lobster stock assessment by adjusting the values of coefficients for select parameters. With appropriate coefficients for the initial abundance, recruitment, and seasonal encounter probability levels, the tuned IBLS accurately simulated the historical landings. Given the uncertainty in future American lobster recruitment, the tuned IBLS was then used to evaluate the effectiveness of current management regulations under different levels of recruitment. [ABSTRACT FROM AUTHOR]

A postflexion (tholichthys-stage) Chaetodon ocellatus (Spotfin Butterflyfish) was captured in a Southern Maine estuary in October 2017. As the Gulf of Maine continues its current warming trend, we anticipate an increase in the presence of such transient tropical species. [ABSTRACT FROM AUTHOR]

Empirical discard mortality rate estimates are vital to both stock assessments and fishery management, especially for stocks that experience high discard rates, such as in the recreational rod‐and‐reel fishery for Haddock Melanogrammus aeglefinus in the Gulf of Maine. The objective of the present study was to derive a fishery‐scale discard mortality rate estimate for Haddock that are captured and released in the Gulf of Maine recreational fishery by combining results of an electronic‐tagging telemetry experiment with representative fishery‐dependent survey data. Scientific personnel and industry partners collected data on a suite of biological, environmental, and technical covariates from 2,442 Haddock caught under authentic fishery scenarios during 2015. Despite being a physoclistous species, <1% of sampled Haddock were observed to die when brought onboard and only ~3% floated upon release. Postrelease fate was then monitored for 154 Haddock using passive acoustic telemetry and determined using a semiquantitative classification procedure reliant upon movement data of Haddock with known fates. The resulting data were analyzed with a parametric survival model to identify which capture‐related covariates influenced mortality. Fishing season and length‐class of Haddock were the most significant predictors of discard mortality, with increased mortality for smaller individuals caught during the autumn, possibly due to increased temperatures. Survival modeling identified that mortality from these covariates occurred primarily after release as compared with during capture and handling. By integrating survival modeling results with fishery‐dependent observations, a fishery‐scale discard mortality rate of 63% was estimated for the 2015 fishing year. Based on these findings, we recommend that fishery managers implement measures to reduce recreational Haddock discards, especially of smaller Haddock during warmer months. [ABSTRACT FROM AUTHOR]

The Windowpane Scophthalmus aquosus stock in Georges Bank and the Gulf of Maine is considered overfished despite the lack of a directed fishery. Windowpane stocks are assessed using an index‐based method relying on the Northeast Fisheries Science Center's (NEFSC; National Oceanic and Atmospheric Administration) fall trawl survey. From 2013 to 2016, the School for Marine Science and Technology (SMAST; University of Massachusetts Dartmouth) conducted a fisheries‐independent trawl survey on the southern portion of Georges Bank, including part of Closed Area II. Using both the NEFSC and SMAST survey catches, we examined seasonal variations in CPUE of Windowpanes as well as their relationship with depth and temperature. Windowpane CPUE was significantly higher in the spring than in the fall and was linked with temperature changes. On the southern portion of Georges Bank, the NEFSC and SMAST surveys had similar relationships between Windowpane catch and temperature. In the spring, Windowpanes were abundant at water temperatures less than 7°C, and they moved out of the area as the temperature increased. In the fall, Windowpane CPUE was higher in warmer water temperatures and decreased as the temperature decreased. As Windowpanes moved out of the area, Fourspot Flounder Paralichthys oblongus replaced them in the habitat. This distribution pattern seems to occur across the whole stock. Our findings suggest that environmental factors can affect the CPUE indices from surveys that are assumed to be consistent, and this should be considered in future assessments. [ABSTRACT FROM AUTHOR]

Since the early twentieth century, the amplitudes of tidal constituents in the Gulf of Maine and Bay of Fundy display clear secular trends that are among the largest anywhere observed for a regional body of water. The M2 amplitude at Eastport, Maine, increased at a rate of 14.1 ± 1.2 cm per century until it temporarily dropped during 1980–1990, apparently in response to changes in the wider North Atlantic. Annual tidal analyses indicate M2 reached an all‐time high amplitude last year (2018). Here we report new estimates of tides derived from nineteenth century water‐level measurements found in the U.S. National Archives. Results from Eastport, Portland, and Pulpit Harbor (tied to Bar Harbor) do not follow the twentieth century trends and indicate that the Gulf of Maine tide changes commenced sometime in the late nineteenth or early twentieth centuries, coincident with a transition to modern rates of sea‐level rise as observed at Boston and Portland. General agreement is that sea level rise alone is insufficient to cause the twentieth‐century tide changes. A role for ocean stratification is suggested by the long‐term warming of Gulf of Maine waters; archival water temperatures at Boston, Portland, and Eastport show increases of ∼2 °C since the 1880s. In addition, a changing seasonal dependence in M2 amplitudes is reflected in a changing seasonal dependence in water temperatures. The observations suggest that models seeking to reproduce Gulf of Maine tides must consider both sea level rise and long‐term changes in stratification. Key Points: Nineteenth‐century water‐level measurements have been recovered for Eastport, Portland, and Pulpit Harbor, MaineLarge twentieth century trends in tidal amplitudes do not extend back into the nineteenth centuryTidal trends are coincident with modern rates of sea level rise at Boston and Portland but changing stratification is likely important [ABSTRACT FROM AUTHOR]

Accurate estimation of the changes of tides is important for sea level prediction and fundamental for local coastal planning. Here we use a novel method, enhanced harmonic analysis (EHA), to extract temporal changes in the response of the nodal modulation of the M 2 tide in the Gulf of Maine. The results show that the temporal variations of nodal amplitudes at four stations in the Gulf of Maine are similar from 1970s to 2013. They all increase in the 1970s to peak values in the 1985s and in the 2000s they decrease to minimum values. The North Atlantic Oscillation (NAO), which is one of the major climate modes in the North Atlantic Ocean, may be responsible for temporal changes in the response of the nodal modulation of the M 2 tide from 1970s to 2013. Also, the results obtained by the new method indicate that the traditional method of harmonic analysis slightly underestimates the trend of M 2 amplitude in the Gulf of Maine. • Temporal changes in the response of the nodal modulation of the M2 tide is extracted by enhanced harmonic analysis. • The traditional method of harmonic analysis slightly underestimates the trend of M2 amplitude in the Gulf of Maine. • Temporal changes in the response of the nodal modulation of the M2 tide may be induced by the NAO and sea level rise. [ABSTRACT FROM AUTHOR]

Hybrid zones provide natural experiments in recombination within and between genomes that may have strong effects on organismal fitness. On the East Coast of North America, two distinct lineages of the European green crab (Carcinus maenas) have been introduced in the last two centuries. These two lineages with putatively different adaptive properties have hybridized along the coast of the eastern Gulf of Maine, producing new nuclear and mitochondrial combinations that show clinal variation correlated with water temperature. To test the hypothesis that mitochondrial or nuclear genes have effects on thermal tolerance, we first measured the response to cold stress in crabs collected throughout the hybrid zone, then sequenced the mitochondrial CO1 gene and two nuclear single nucleotide polymorphisms (SNPs) representative of nuclear genetic lineage. Mitochondrial haplotype had a strong association with the ability of crabs to right themselves at 4.5°C that was sex specific: haplotypes originally from northern Europe gave male crabs an advantage while there was no haplotype effect on righting in female crabs. By contrast, the two nuclear SNPs that were significant outliers in a comparison between northern and southern C. maenas populations had no effect on righting response at low temperature. These results add C. maenas to the shortlist of ectotherms in which mitochondrial variation has been shown to affect thermal tolerance, and suggest that natural selection is shaping the structure of the hybrid zone across the Gulf of Maine. Our limited genomic sampling does not eliminate the strong possibility that mito-nuclear co-adaptation may play a role in the differences in thermal phenotypes documented here. Linkage between mitochondrial genotype and thermal tolerance suggests a role for local adaptation in promoting the spread of invasive populations of C. maenas around the world. [ABSTRACT FROM AUTHOR]

The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of (a) key seasonal processes, patterns, and events; (b) direct evidence for shifts in timing; (c) implications of phenological responses for linked ecological‐human systems; and (d) potential phenology‐focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, occurrence of several larval fishes, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of additional larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro‐invertebrates, and lobster fishery landings. Reduced duration was observed in winter–spring ice‐affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species‐specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long‐term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine and identify opportunities for future research and consideration of phenological changes in adaptation efforts. [ABSTRACT FROM AUTHOR]

The North Atlantic right whale (NARW), Eubalaena glacialis , feeds on zooplankton, particularly copepods of the genus Calanus. We quantified interannual variation in anomalies of abundance and biomass of Calanus spp. and near-surface and near-bottom ocean temperature and salinity from 19 subregions spanning the Gulf of Maine–Georges Bank (GoM–GBK), Scotian Shelf (SS), Gulf of St. Lawrence (GSL) and Newfoundland and Labrador Shelves. We analyzed time series from 1977 to 2016 in GoM–GBK, 1982 to 2016 in southwest GSL and 1999 to 2016 in remaining areas. Calanus finmarchicus dominated abundance and biomass, except in the GSL where Calanus hyperboreus was abundant. The biomass of Calanus spp. declined in many subregions over years 1999–2016 and was negatively correlated with sea surface temperature in GoM–GBK and on the SS. We detected ''regime shifts" to lower biomass of Calanus spp. in the GoM–GBK in 2010 and on the SS in 2011. In the GoM–GBK, shifts to lower biomass of C. finmarchicus coincided with shifts to warmer ocean temperature and with published reports of changes in spatial distribution and reduced calving rate of NARW. We hypothesize that warming has negatively impacted population levels of Calanus spp. near their southern range limit, reducing the availability of prey to NARW. [ABSTRACT FROM AUTHOR]

Seaweed aquaculture is a relatively young industry in the United States compared to Asian countries. Early attempts at seaweed aquaculture in California, Washington State, New York and the Gulf of Maine in the 1980s and 1990s did not result in commercial production but provided important lessons. Since 2010, commercial cultivation of kelp (Saccharina latissima, Laminaria digitata, and Alaria esculenta) and other seaweeds (Palmaria palmata and Porphyra umbilicalis) began in the Gulf of Maine and Long Island Sound. Seaweed aquaculture is now a fast-growing maritime industry, especially in New England. If seaweed aquaculture is to maintain its momentum, it is important to (1) emphasise the environmental benefits; (2) domesticate a variety of local species; and (3) diversify seaweed products for food, animal feed, phycocolloids, cosmeceuticals, nutraceuticals, and ultimately biofuels if it becomes economically viable due to the cost of production. The exclusive economic zone (EEZ) of the United States offers opportunities for expansion of seaweed aquaculture in an area greater than the entire land mass of the United States and with limited user conflicts. This study reviews the past and current status of seaweed aquaculture in the United States and discusses potential opportunities and challenges of open-water seaweed aquaculture. [ABSTRACT FROM AUTHOR]

The cribrimorph bryozoan Cribrilina (Juxtacribrilina) mutabilis (Ito, Onishi and Dick, 2015), originally described from Hokkaido, Japan, is reported for the first time in the Gulf of Maine and the whole of the Northwest Atlantic coast. In September 2018, numerous colonies of C. mutabilis were collected from eelgrass (Zostera marina Linnaeus, 1753) beds near Clapboard and Mackworth Islands, and Hog Island Ledge, all located within inner Casco Bay, Maine. Bryozoan colonies encrusted eelgrass, rockweed (Ascophyllum nodosum (Linnaeus) LeJolis, 1863), and laminarian drift algae. Situated near the discovery location, the city of Portland (Maine, USA) is an active seaport, suggesting introduction through shipping as a likely introduction mechanism. The North Sea is hypothesized to be the most probable area for the source population. Since C. mutabilis appears to have high potential for introduction, it likely occurs on other parts of the Northwest Atlantic coast where it has yet to be identified and recorded. [ABSTRACT FROM AUTHOR]

The drivers of latitudinal differences in the phylogenetic and ecological composition of communities are increasingly studied and understood, but still little is known about the factors underlying morphological differences. High-resolution, three-dimensional morphological data collected using computerized micro-tomography (micro-CT) allows comprehensive comparisons of morphological diversity across latitude. Using marine bivalves as a model system, this study combines 3D shape analysis (based on a new semi-automated procedure for placing landmarks and semilandmarks on shell surfaces) with non-shape traits: centroid size, proportion of shell to soft-tissue volume, and magnitude of shell ornamentation. Analyses conducted on the morphology of 95% of all marine bivalve species from two faunas along the Atlantic coast of North America, the tropical Florida Keys and the boreal Gulf of Maine, show that morphological shifts between these two faunas, and in phylogenetic and ecological subgroups shared between them, occur as changes in total variance with a bounded minimum rather than directional shifts. The dispersion of species in shell-shape morphospace is greater in the Gulf of Maine, which also shows a lower variance in ornamentation and size than the Florida Keys, but the faunas do not differ significantly in the ratio of shell to internal volume. Thus, regional differences conform to hypothesized effects of resource seasonality and predation intensity, but not to carbonate saturation or calcification costs. The overall morphological differences between the regional faunas is largely driven by the loss of ecological functional groups and family-level clades at high latitudes, rather than directional shifts in morphology within the shared groups with latitude. Latitudinal differences in morphology thus represent a complex integration of phylogenetic and ecological factors that are best captured in multivariate analyses across several hierarchical levels. [ABSTRACT FROM AUTHOR]

Fishery-dependent monitoring programs provide valuable information for the assessment and management of fishery stocks. The quality of the data and subsequent stock assessment are largely influenced by sampling design and sample size. The Lobster Sea Sampling Program in the Gulf of Maine yields critical information for the assessment of American lobster (Homarus americanus). To facilitate the use of an on-boat tablet-based data entry system, which will replace the current voice recording system, the sampling program requires development of a subsampling procedure to account for a decrease in the data recording speed after the new data entry system is implemented. We evaluated the performance of four potential subsampling strategies, including possible combinations of simple random vs. systematic subsampling with fixed subsample size vs. subsample size in proportion to reference data. Proportional subsampling showed lower relative estimation error and relative bias compared to subsampling with fixed subsample size. Within the two proportional subsampling strategies, systematic subsampling showed similar precision and accuracy compared to random subsampling, but systematic subsampling is more feasible to be conducted onboard. We concluded that the systematic subsampling of 50% of reference data could reduce current sampling effort but still capture the temporal trend of reference data. The simulation approach developed in this study can also be applied to optimize other fisheries-dependent monitoring programs. [ABSTRACT FROM AUTHOR]

Management strategy evaluation (MSE) is an effective tool to evaluate the performance of harvest control rules (HCRs) and alternative management strategies. However, a comprehensive MSE framework advising management is still absent for the severely depleted Gulf of Maine (GoM) cod (Gadus morhua). In the present study, we developed a conceptual MSE framework and conditioned on this stock utilizing stock-specific parameterization. We highlighted the simulation of a few key processes with semi-independent sub-models and accounted for uncertainties from multiple sources. The simulated population dynamics was calibrated and validated against the historical trend in hindcasting. Forecasting simulations were also conducted and validated to examine the effectiveness in the context of uncertainty. Hindcasting results suggested that the calibrated MSE framework could capture the stock dynamics assuming different recruitment dynamics indicated by residuals lower than 5%. Forecasting stochastic runs demonstrated a minor disparity between management effects of fishing-mortality-based and catch-based HCRs when the segregated stock recruitment relationship was adopted with a difference in simulated spawning stock biomass lower than 10%. Additionally, the results were comparable to assessment and projections made in the stock assessment, indicating the robustness of the framework. The framework can potentially help disentangle complex issues related to the mixed fishery, decision-making, and performance evaluation of a monitoring system. [ABSTRACT FROM AUTHOR]

Biodiversity of zooplankton is central to the functioning of ocean ecosystems, yet morphological taxonomic analysis requires teams of experts and detailed examination of many samples. Metabarcoding (DNA sequencing of short amplified regions of one or a few genes from environmental samples) is a powerful tool for analysis of the composition and diversity of natural communities. The 18S rRNA V9 hypervariable region was sequenced for 26 zooplankton samples collected from the Gulf of Maine, Georges Bank, and Mid-Atlantic Bight during ecosystem monitoring surveys by the U.S. Northeast Fisheries Science Center during 2002–2012. A total of 7 648 033 sequences and 22 072 operational taxonomic units (OTUs) were identified and classified into 28 taxonomic groups of plankton. Comparative analysis of molecular (V9 sequence numbers) and morphological (abundance counts) focused on seven taxonomic groups and revealed similar patterns of variation among years and regions. Sequence numbers and abundance counts showed positive correlation for all groups, with significant correlations (p  < 0.05) for Calanoida, Gastropoda, and Chaetognatha. Shannon diversity index values calculated using sequence numbers and abundance counts showed highly significant correlation (r  = 0.625; p  < 0.001) across all regions during 2002–2012. This study demonstrates the potential of metabarcoding for time-series analysis of zooplankton biodiversity, ocean ecosystem assessment, and fisheries management. [ABSTRACT FROM AUTHOR]

Changes in bottom-up forcing are fundamental drivers of fish population dynamics. Recent literature has highlighted the need to incorporate the role of dynamic environmental conditions in stock assessments as a key step towards adaptive fishery management. Combining a bioclimate envelope model and a population dynamic model, we propose a model-based approach that can incorporate ecosystem products into single-species stock assessments. The framework was applied to a commercially important American lobster (Homarus americanus) stock in the Northwest Atlantic. The bioclimate envelope model was used to hindcast temporal variability in a lobster recruitment habitat suitability index (HSI) using bottom temperature and salinity. The climate-driven HSI was used to inform the lobster recruitment dynamics within the size-structured population dynamics model. The performance of the assessment model with an environment-explicit recruitment function is evaluated by comparing relevant assessment outputs such as recruitment, annual fishing mortality, and magnitude of retrospective biases. The environmentally-informed assessment model estimated (i) higher recruitment and lower fishing mortality and (ii) reduced retrospective patterns. This analysis indicates that climate-driven changes in lobster habitat suitability contributed to increased lobster recruitment and present potential improvement to population assessment. Our approach is extendable to other stocks that are impacted by similar environmental variability. [ABSTRACT FROM AUTHOR]

Surface seawater partial pressure of CO 2 (p CO 2) is a critical parameter in the quantification of air-sea CO 2 flux, which further plays an important role in quantifying the global carbon budget and understanding ocean acidification. Yet, the remote estimation of p CO 2 in coastal waters (under influences of multiple processes) has been difficult due to complex relationships between environmental variables and surface p CO 2. To date there is no unified model to remotely estimate surface p CO 2 in oceanic regions that are dominated by different oceanic processes. In our study area, the Gulf of Mexico (GOM), this challenge is addressed through the evaluation of different approaches, including multi-linear regression (MLR), multi-nonlinear regression (MNR), principle component regression (PCR), decision tree, supporting vector machines (SVMs), multilayer perceptron neural network (MPNN), and random forest based regression ensemble (RFRE). After modeling, validation, and extensive tests using independent cruise datasets, the RFRE model proved to be the best approach. The RFRE model was trained using data comprised of extensive p CO 2 datasets (collected over 16 years by many groups) and MODIS (Moderate Resolution Imaging Spectroradiometer) estimated sea surface temperature (SST), sea surface salinity (SSS), surface chlorophyll concentration (Chl), and diffuse attenuation of downwelling irradiance (Kd). This RFRE-based p CO 2 model allows for the estimation of surface p CO 2 from satellites with a spatial resolution of ~1 km. It showed an overall performance of a root mean square difference (RMSD) of 9.1 μatm, with a coefficient of determination (R2) of 0.95, a mean bias (MB) of −0.03 μatm, a mean ratio (MR) of 1.00, an unbiased percentage difference (UPD) of 0.07%, and a mean ratio difference (MRD) of 0.12% for p CO 2 ranging between 145 and 550 μatm. The model, with its original parameterization, has been tested with independent datasets collected over the entire GOM, with satisfactory performance in each case (RMSD of ≤~10 μatm for open GOM waters and RMSD of ≤~25 μatm for coastal and river-dominated waters). The sensitivity of the RFRE-based p CO 2 model to uncertainties of each input environmental variable was also thoroughly examined. The results showed that all induced uncertainties were close to, or within, the uncertainty of the model itself with higher sensitivity to uncertainties in SST and SSS than to uncertainties in Chl and Kd. The extensive validation, evaluation, and sensitivity analysis indicate the robustness of the RFRE model in estimating surface p CO 2 for the range of 145–550 μatm in most GOM waters. The RFRE model approach was applied to the Gulf of Maine (a contrasting oceanic region to GOM), with local model training. The results showed significant improvement over other models suggesting that the RFRE may serve as a robust approach for other regions once sufficient field-measured p CO 2 data are available for model training. • Remote sensing of ocean surface p CO 2 in complex regions has large uncertainties. • A machine learning approach is developed for the Gulf of Mexico and Gulf Maine. • The approach shows significantly improved performance over other approaches. • Uncertainties in the estimated surface p CO 2 are within 10 μatm for a large range. [ABSTRACT FROM AUTHOR]

This study uses the Maine Department of Marine Resources Lobster Sea Sampling data (2000–2016) and logistic models to develop the first time series for the timing and suddenness of onset of the initial intra‐annual molt of American lobster in the Gulf of Maine (GoM), an annual fishery recruitment event crucial to fishermen. Data from three GoM regions (eastern, central, and western coastal Maine) were further divided by sex and estimated maturity of sampled lobsters for analysis. We found differences in the patterns of initial molt timing and suddenness between the regions, sexes, and stages of maturity. Using the Northeast Coastal Ocean Forecasting System hindcast temperatures, seasonal accumulated degrees above 5°C were used to describe the thermal history for each region at ocean depths of about 5 and 110 m. These temperature metrics were used in generalized linear models to investigate the potential effects of seasonal temperatures on the initial molt season. Results showed that initial intra‐annual molting of lobsters was variable from 2000 to 2016, with periods of both earlier and more sudden molts and later and more protracted molts. Warmer temperatures, specifically inshore temperatures, were generally associated with an earlier molt, but without complete uniformity in the direction and magnitude across seasons, regions, and lobster demographics. We also discuss why developing molt time series and quantifying the connection to the bottom temperatures are necessary and emphasized why existing monitoring programs and the applied quantification techniques herein make this relationship difficult to quantify. [ABSTRACT FROM AUTHOR]

The sea louse, Lepeophtheirus salmonis (Krøyer 1837), is a significant parasite of farmed salmon throughout the Northern Hemisphere. Management of on‐farm louse populations can be improved by understanding the role that wild fish play in sustaining and providing refuge for the local population of sea lice. In this study, 1,064 sticklebacks were captured. Of these animals, 176 individuals were carrying a total of 238 sea lice, yielding a prevalence and intensity of 16.5% and 1.4 lice per fish, respectively. Detailed examination of the sea lice on the three‐spined sticklebacks captured in Cobscook Bay found two L. salmonis individuals using three‐spined sticklebacks as hosts. A 2012 survey of wild fish in Cobscook Bay, Maine, found multiple wild hosts for Caligus elongatus (von Nordmann 1832), including three‐spined sticklebacks (Gasterosteus aculeatus L.), but no L. salmonis were found in this earlier study. [ABSTRACT FROM AUTHOR]

The size at which female American lobsters Homarus americanus (H. Milne Edwards, 1837) reach maturity was determined for females collected from inshore (< 3 nautical miles, or 5.5 km) Boothbay Harbor (BBH), Maine, USA in 2018. A total of 272 females were collected during a three-week period in the spring and each female was assigned a maturity status (immature or mature) based on ovarian staging. These determinations were then compared to two similar female-maturity studies undertaken in BBH by the Maine Department of Marine Resources over the last 50 years. The comparison revealed that the length at which 50% of females reach maturity has decreased by 5 mm over the last 25 years and a significant difference between maturity ogives generated over time in BBH. Cement-gland stage was also recorded for all females and further analysis revealed no significant difference between maturity ogives generated using ovarian and cement-gland staging. Results indicate that cement-gland staging is an effective maturity assessment method in female lobsters from this region. Because there is a well-documented relationship between temperature and size at maturity in crustaceans, we also examined changes in sea-surface temperature during this period in BBH. We found that the region has warmed significantly over this period of time with extreme high temperatures occurring more frequently during the last 25 years. Our results can be used to update key parameters in the stock-assessment model related to growth and egg production in the Gulf of Maine/George's Bank stock. These findings can also be used to inform future management decisions related to the carapace length of harvested lobsters and the preservation of mature females. [ABSTRACT FROM AUTHOR]

Absolute abundances of prokaryotes are typically determined by FISH. Due to the lack of a universal conserved gene among all viruses, metagenomic fragment recruitment is commonly used to estimate the relative viral abundance. However, the paucity of absolute virus abundance data hinders our ability to fully understand how viruses drive global microbial populations. The cosmopolitan marine Pelagibacter ubique is host for the highly widespread HTVC010P pelagiphage isolate and the extremely abundant uncultured virus vSAG 37-F6 recently discovered by single-virus genomics. Here we applied droplet digital PCR (ddPCR) to calculate the absolute abundance of these pelagiphage genotypes in the Mediterranean Sea and the Gulf of Maine. Abundances were between 360 and 8,510 virus mL-1 and 1,270–14,400 virus mL-1 for vSAG 37-F6 and HTVC010P, respectively. Illumina PCR-amplicon sequencing corroborated the absence of ddPCR non-specific amplifications for vSAG 37-F6, but showed an overestimation of 6% for HTVC010P from off-targets, genetically unrelated viruses. Absolute abundances of both pelagiphages, two of the most abundance marine viruses, suggest a large viral pelagiphage diversity in marine environments, and show the efficiency and power of ddPCR to disentangle the structure of marine viral communities. Results also highlight the need for a standardized workflow to obtain accurate quantification that allows cross data comparison. [ABSTRACT FROM AUTHOR]

• Three genetically distinct clusters of Alexandrium catenella were identified in the Gulf of Maine. • Each cluster contained representatives from different sub-regions, highlighting the connectivity and dispersal throughout the region. • This shared diversity could result from cyst beds containing a mix of resting stages from different genetic clusters. • Rapid spatiotemporal genetic differentiation was observed in local blooms, likely driven by nutrient concentrations. Paralytic Shellfish Poisoning (PSP) caused by the dinoflagellate Alexandrium catenella is a well-known global syndrome that negatively impacts human health and fishery economies. Understanding the population dynamics and ecology of this species is thus important for identifying determinants of blooms and associated PSP toxicity. Given reports of extensive genetic heterogeneity in the toxicity and physiology of Alexandrium species, knowledge of genetic population structure in harmful algal species such as A. catenella can also facilitate the understanding of toxic bloom development and ecological adaptation. In this study we employed microsatellite markers to analyze multiple A. catenella strains isolated from several sub-regions in the Gulf of Maine (GoM) during summer blooms, to gain insights into the sources and dynamics of this economically important phytoplankton species. At least three genetically distinct clusters of A. catenella were identified in the GoM. Each cluster contained representatives from different sub-regions, highlighting the extent of connectivity and dispersal throughout the region. This shared diversity could result from cyst beds created by previous coastal blooms, thereby preserving the overall diversity of the regional A. catenella population. Rapid spatiotemporal genetic differentiation of A. catenella populations was observed in local blooms, likely driven by natural selection through environmental conditions such as silicate and nitrate/nitrite concentrations, emphasizing the role of short-term water mass intrusions and biotic processes in determining the diversity and dynamics of marine phytoplankton populations. Given the wide-spread intraspecific diversity of A. catenella in GoM and potentially elsewhere, harmful algal blooms will likely persist in many regions despite global warming and changing environmental conditions in the future. Selection of different genetic lineages through variable hydrological conditions might impact toxin production and profiles of future blooms, challenging HAB control and prediction of PSP risk in the future. [ABSTRACT FROM AUTHOR]

Developing high-resolution, well-dated, marine proxies of environmental, climatic, and oceanographic conditions is critical in order to advance our understanding of the ocean's role in the global climate system. While some work has investigated bulk and compound specific stable nitrogen isotope (δ15N) values in bivalve shells as proxies for environmental variability, the small concentrations of nitrogen found in the organic matrix of the shell calcium carbonate (hereafter carbonate) makes developing high resolution records challenging. This study investigates the potential of using the bulk and amino acid δ15N values of bivalve periostracum, the protein layer on the outside of the shell, as a proxy archive of nitrogen cycling processes and water source variability. Bulk δ15N values were measured on the periostracum, carbonate, and adductor muscle of Arctica islandica shells collected in the Gulf of Maine. Increased variability of isotopic values across growth lines compared to along growth lines support mechanistic reasoning based on growth processes that periostracum is recording changes in δ15N values over the course of the clam's lifetime (up to 500 years). In addition, the statistically significant relationship between periostracum δ15N values and contemporaneous carbonate δ15N values of the same shell (r = 0.82, p < 0.0001, n = 40) suggests that periostracum preserves a similar δ15N signal to that preserved in the carbonate. This finding, coupled with the fact that source amino acid δ15N values of periostracum are similar to that of the adductor muscle and the particulate organic matter (POM) consumed by the clam, suggests that periostracum bulk δ15N values reflect the δ15N values of the clam's food source. The isotopic offsets between periostracum, carbonate, and adductor muscle δ15N values are primarily caused by differences in amino acid composition of the different tissue types, as evidenced by isotope mass balance calculations, although may also be related to differences in δ15N values of the individual amino acids of the different tissue types, especially for the trophic amino acids. Compound specific δ15N analyses of the periostracum of A. islandica shells were used to determine that the calculated trophic position of the clams in this study (1.4 ± 0.4) did not change significantly between 1783 and 1997. Phenylalanine δ15N values over the last 70 years show similar trends to that of the bulk record, suggesting that changes in bulk δ15N values over that time period are related to changes in baseline δ15N values. Periostracum δ15N values from shells collected in the western Gulf of Maine have decreased by ∼1‰ since the mid-1920s. This trend (−0.008‰/year) is not statistically different from the trend of previously published δ15N values of deep-sea corals from the entrance to the Gulf of Maine over the same time period. This coral record has been shown to indicate a shift in water source in the region and therefore the similarity between the two records suggest that changes in periostracum δ15N values are reflecting broader North Atlantic hydrographic changes. Our study introduces a new, high-resolution, and absolutely dated paleoceanographic proxy of baseline δ15N values, presenting the opportunity for future reconstructions of aspects of nitrogen cycling and water source changes in the global oceans. [ABSTRACT FROM AUTHOR]