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The increasing frequency and intensity of heatwaves may represent a significant challenge for predicting vulnerability of populations in a warming ocean. The direct impacts of heatwaves on populations depend on the relative position of environmental temperatures to the thermal performance curve optima. If thermal performance curves are static, the effects of heatwaves may therefore change seasonally over the annual temperature cycle. However, these seasonal changes in the effects of heatwaves may be dampened by corresponding variation in thermal performance curves which, in organisms with relatively short generation times, may be driven by phenotypic plasticity as well as genetic differentiation. Here we investigate the effects of seasonal timing and duration on the impacts of heatwaves in the ecologically important copepod congenersAcartia tonsaandAcartia hudsonica, and test the hypotheses that 1) seasonal variation in thermal performance curves will reduce overall population vulnerability to heatwaves, and 2) that seasonal variation in TPCs will prevent negative transgenerational effects of heatwave. We characterized seasonal variation in thermal performance curves for several fitness-related traits. These experiments uncovered strong seasonal variation in the thermal performance curves ofAcartia tonsa, and indicate that this variation buffers against negative effects of simulated heatwaves. We also quantified both direct and trans-generational effects of different duration heatwaves on copepods collected at various times throughout the season using simulated heatwave experiments. There was no consistent pattern in the transgenerational effects of parental exposure to heatwaves, which may indicate that seasonal variation in thermal performance curves reduces the effects of parental stress on offspring performance. Our results show that seasonal variation in thermal performance curves will likely play an important role in limiting the adverse effects of heatwaves on populations.

Parasitism has strong effects on community dynamics. Given the detrimental effects parasites have on host health, infection or infestation might be expected to reduce upper thermal limits, increasing the vulnerability of host species to future climate change. Copepods are integral components of aquatic food webs and biogeochemical cycles. They also serve as intermediate hosts in the life cycle of parasitic isopods in the family Bopyridae. Given the important effects both copepods and isopod parasites play in aquatic communities, it is important to understand how the interaction between parasite and host affects thermal limits in order to better predict how community dynamics may change in a warming climate. Here we examined the effect of infestation by larvae of a bopyrid isopod on cosmopolitan copepodAcartia tonsato test the hypothesis that infestation reduces thermal limits. To aid with this work, we developed an affordable, highly portable system for measuring critical thermal maxima of small ectotherms. We also used meta-analysis to summarize the effects of parasitism on critical thermal maxima in a wider range of taxa to help contextualize our findings. Contrary to both our hypothesis and the results of previous studies, we observed no reduction of thermal limits by parasitism inA. tonsa. These results suggest that life history of the host and parasite may interact to determine how parasite infestation affects environmental sensitivity.

Significance Resilience to global change will require adaptation to multiple concurrent environmental changes. However, it is unclear if adaptations to multiple stressors can be predicted from the sum of single-stressor adaptation. To answer this question, we experimentally evolved a marine copepod to warming, acidification, and their combination, finding that copepods were able to adapt to all conditions over 25 generations. Warming was a much stronger selective pressure than acidification alone and under multiple-stressor conditions. Nevertheless, the multiple-stressor response to selection was synergistic and unique from either single stressor. Thus, adaptation to single stressors may not reveal adaptive potential or mechanisms of adaptation under multiple stressors, demonstrating the complexity of predicting adaptive responses under multifaceted environmental change. Abstract Metazoan adaptation to global change relies on selection of standing genetic variation. Determining the extent to which this variation exists in natural populations, particularly for responses to simultaneous stressors, is essential to make accurate predictions for persistence in future conditions. Here, we identified the genetic variation enabling the copepod Acartia tonsa to adapt to experimental ocean warming, acidification, and combined ocean warming and acidification (OWA) over 25 generations of continual selection. Replicate populations showed a consistent polygenic response to each condition, targeting an array of adaptive mechanisms including cellular homeostasis, development, and stress response. We used a genome-wide covariance approach to partition the allelic changes into three categories: selection, drift and replicate-specific selection, and laboratory adaptation responses. The majority of allele frequency change in warming (57%) and OWA (63%) was driven by shared selection pressures across replicates, but this effect was weaker under acidification alone (20%). OWA and warming shared 37% of their response to selection but OWA and acidification shared just 1%, indicating that warming is the dominant driver of selection in OWA. Despite the dominance of warming, the interaction with acidification was still critical as the OWA selection response was highly synergistic with 47% of the allelic selection response unique from either individual treatment. These results disentangle how genomic targets of selection differ between single and multiple stressors and demonstrate the complexity that nonadditive multiple stressors will contribute to predictions of adaptation to complex environmental shifts caused by global change.

Short-term, acute warming events are increasing in frequency across the world’s oceans. For short-lived species like most copepods, these extreme events can occur over both within- and between-generational time scales. Yet, it is unclear whether exposure to acute warming during early life stages of copepods can cause lingering effects on metabolism through development, even after the event has ended. These lingering effects would reduce the amount of energy devoted to growth and affect copepod population dynamics. We exposed nauplii of an ecologically important coastal species, Acartia tonsa, to a 24-hour warming event (control: 18°C; treatment: 28°C), and then tracked individual respiration rate, body length, and stage duration through development. As expected, we observed a decrease in massspecific respiration rates as individuals developed. However, exposure to acute warming had no effect on the ontogenetic patterns in per-capita or mass-specific respiration rates, body length, or development time. The lack of these carryover effects through ontogeny suggests within-generational resilience to acute warming in this copepod species.

Whether populations can adapt to predicted climate change conditions, and how rapidly, are critical questions for the management of natural systems. Experimental evolution has become an important tool to answer these questions. In order to provide useful, realistic insights into the adaptive response of populations to climate change, there needs to be careful consideration of how genetic differentiation and phenotypic plasticity interact to generate observed phenotypic changes. We exposed three populations of the widespread copepod Acartia tonsa (Crustacea) to chronic, sublethal temperature selection for 15 generations. We generated thermal survivorship curves at regular intervals both during and after this period of selection to track the evolution of thermal tolerance. Using reciprocal transplants between ambient and warming conditions, we also tracked changes in the strength of phenotypic plasticity in thermal tolerance. We observed significant increases in thermal tolerance in the Warming lineages, while plasticity in thermal tolerance was strongly reduced. We suggest these changes are driven by a negative relationship between thermal tolerance and plasticity in thermal tolerance. Our results indicate that adaptation to warming through an increase in thermal tolerance might not reduce vulnerability to climate change if the increase comes at the expense of tolerance plasticity. These results illustrate the importance of considering changes in both a trait of interest and the trait plasticity during experimental evolution.

Copepods are key components of aquatic habitats across the globe. Understanding how they respond to warming is important for predicting the effects of climate change on aquatic communities. Lethal thermal limits may play an important role in determining responses to warming. Thermal tolerance can vary over several different spatial and temporal scales, but we still lack a fundamental understanding of what drives the evolution of these patterns in copepods. In this Horizons piece, we provide a synthesis of global patterns in copepod thermal tolerance and potential acclimatory capacities. Copepod thermal tolerance increases with maximum annual temperature. We also find that the effects of phenotypic plasticity on thermal tolerance are negatively related to the magnitude of thermal tolerance, suggesting a potential trade-off between these traits. Our ability to fully describe these patterns is limited, however, by a lack of spatial, temporal and phylogenetic coverage in copepod thermal tolerance data. We indicate several priority areas for future work on copepod thermal tolerance, and accompanying suggestions regarding experimental design and methodology.

Organisms experience variation in the thermal environment on several different temporal scales, with seasonality being particularly prominent in temperate regions. For organisms with short generation times, seasonal variation is experienced across, rather than within, generations. How this affects the seasonal evolution of thermal tolerance and phenotypic plasticity is understudied, but has direct implications for the thermal ecology of these organisms. Here we document intra‐annual patterns of thermal tolerance in two species of Acartia copepods (Crustacea) from a highly seasonal estuary, showing strong variation across the annual temperature cycle. Common garden, split‐brood experiments indicate that this seasonal variation in thermal tolerance, along with seasonal variation in body size and phenotypic plasticity, is likely affected by genetic polymorphism. Our results show that adaptation to seasonal variation is important to consider when predicting how populations may respond to ongoing climate change., We examined seasonal variation in thermal performance curves of a short‐lived marine copepod. Experiments with unacclimated individuals from the field and laboratory common garden experiments indicate that the observed seasonal variation in both thermal tolerance and phenotypic plasticity likely has a genetic basis.

Adaptive evolution and phenotypic plasticity will fuel resilience in the geologically unprecedented warming and acidification of the earth’s oceans, however, we have much to learn about the interactions and costs of these mechanisms of resilience. Here, using 20 generations of experimental evolution followed by three generations of reciprocal transplants, we investigated the relationship between adaptation and plasticity in the marine copepod, Acartia tonsa, in future global change conditions (high temperature and high CO2). We found parallel adaptation to global change conditions in genes related to stress response, gene expression regulation, actin regulation, developmental processes, and energy production. However, reciprocal transplantation showed that adaptation resulted in a loss of transcriptional plasticity, reduced fecundity, and reduced population growth when global change-adapted animals were returned to ambient conditions or reared in low food conditions. However, after three successive transplant generations, global change-adapted animals were able to match the ambient-adaptive transcriptional profile. Concurrent changes in allele frequencies and erosion of nucleotide diversity suggest that this recovery occurred via adaptation back to ancestral conditions. These results demonstrate that while plasticity facilitated initial survival in global change conditions, it eroded after 20 generations as populations adapted, limiting resilience to new stressors and previously benign environments.

Short-term, acute warming events are increasing in frequency across the world’s oceans. For short-lived species like most copepods, these extreme events can occur over both within- and between-generational time scales. Yet, it is unclear whether exposure to acute warming during early life stages of copepods can cause lingering effects on metabolism through development, even after the event has ended. These lingering effects would reduce the amount of energy devoted to growth and affect copepod population dynamics. We exposed nauplii of an ecologically important coastal species, Acartia tonsa, to a 24-hour warming event (control: 18°C; treatment: 28°C), and then tracked individual respiration rate, body length, and stage duration through development. As expected, we observed a decrease in mass-specific respiration rates as individuals developed. However, exposure to acute warming had no effect on the ontogenetic patterns in per-capita or mass-specific respiration rates, body length, or development time. The lack of these carryover effects through ontogeny suggests within-generational resilience to acute warming in this copepod species.

The tectonic evolution of the Labrador-Baffin Seaway began with Early Cretaceous extension between Greenland and North America, resulting in the development of basins infilled with nonmarine and shallow-marine clastic strata. The Late Cretaceous was a time of continued rifting and local subsidence, with deposition of widespread deeper water marine mud and localized sand deposits. Seafloor spreading began in the south in the Latest Cretaceous and propagated throughout the seaway by the Early Paleocene. Regional seafloor spreading coincided with the onset of significant volcanism in the Davis Strait to central West Greenland region, as well as a regional regression. A change in the spreading direction around the Paleocene- Eocene boundary, was accompanied by strike-slip motion in the Davis Strait and Baffin Bay, deformation and basin inversion, and development of regional unconformities. After seafloor spreading ceased in the late Eocene, the seaway was filled by upper Paleogene to Recent sediments, with clinoform progradation building the modern-day shelves.

The stratigraphy and the geological evolution of the West Greenland margin from the Labrador Sea to Baffin Bay in both the onshore and offshore areas are described. The primary data sets include seismic reflection surveys, wells, and outcrops. In addition, seabed samples, seismic refraction and magnetic data, onshore and offshore maps, and stratigraphic compilations were used. The basins of the West Greenland continental margin are described in three regions from the south to the north: southern West Greenland basins, central West Greenland basins, and northern West Greenland basins. Each region includes a description of the stratigraphy and evolution from the Archean to the Quaternary, divided into six phases: pre-rift and early extension, early rift, subsidence and rifting, late rift, drift, and post-drift. Finally, the regions are correlated and described in a tectonostratigraphic context together with analogues from the Canadian conjugate margin.

A formidable challenge for global change biologists is to predict how natural populations will respond to the emergence of conditions not observed at present, termed novel climates. Popular approaches to predict population vulnerability are based on the expected degree of novelty relative to the amplitude of historical climate fluctuations experienced by a population. Here, we argue that predictions focused on amplitude may be inaccurate because they ignore the predictability of environmental fluctuations in driving patterns of evolution and responses to climate change. To address this disconnect, we review major findings of evolutionary theory demonstrating the conditions under which phenotypic plasticity is likely to evolve in natural populations, and how plasticity decreases population vulnerability to novel environments. We outline key criteria that experimental studies should aim for to effectively test theoretical predictions, while controlling for the degree of climate novelty. We show that such targeted tests of evolutionary theory are rare, with marine systems being overall underrepresented in this venture despite exhibiting unique opportunities to test theory. We conclude that with more robust experimental designs that manipulate both the amplitude and predictability of fluctuations, while controlling for the degree of novelty, we may better predict population vulnerability to climate change.

Highlights: • Copepods more efficiently assimilated methylmercury than inorganic mercury. • Algal size can consequentially influence uptake for different mercury species. • The fraction of methylmercury transferred to zooplankton varies with algae species. • Uptake of mercury species into algae is active. • Demonstrated the usefulness of stable isotopes approaches. Mercury (Hg) and methylmercury (CH3Hg) are found at trace levels in most marine waters. These species, particularly CH3Hg, then ominously bioaccumulate through marine food chains eventually reaching potentially harmful levels in top oceanic wildlife. Accordingly, it is important to measure and evaluate uptake at environmentally relevant concentrations where trophic transfer initiates; during uptake in primary producers, and consumption by plankton grazers. Experiments using cultured copepods (Acartia tonsa) and field zooplankton assemblages were performed with two different sized diatom species labeled with stable isotopes of inorganic Hg (Hg-200) and CH3Hg ((CH3Hg)-Hg-199) at different concentrations. We observed size-specific effects on algal uptake and transfer to copepods, in addition to effects of Hg species concentration. Prey size effects were likewise observed on copepod assimilation efficiencies (AE). Average AE of Hg-200 for copepods feeding on smaller diatoms was 50%, and 39% for larger diatoms. The AEs were much greater for (CH3Hg)-Hg-199, yielding 71% for the smaller and 88% for the larger diatoms. These experiments add evidence demonstrating a significant relationship between Hg and CH3Hg exposure concentration and subsequent algal uptake and transfer to zooplankton. Furthermore, results imply that facilitated uptake of CH3Hg into algae occurs at low (similar to pM) concentrations, which has been suggested but not confirmed in previous research.

Predicting the response of marine animals to climate change is hampered by a lack of multigenerational studies on evolutionary adaptation, particularly to combined ocean warming and acidification (OWA). We provide evidence for rapid adaptation to OWA in the foundational copepod species, Acartia tonsa, by assessing changes in population fitness on the basis of a comprehensive suite of life-history traits, using an orthogonal experimental design of nominal temperature (18 °C, 22 °C) and $$p_{\mathrm{{CO}}_2}$$ (400, 2,000 µatm) for 25 generations (~1 year). Egg production and hatching success initially decreased under OWA, resulting in a 56% reduction in fitness. However, both traits recovered by the third generation, and average fitness was reduced thereafter by only 9%. Antagonistic interactions between warming and acidification in later generations decreased survival, thereby limiting full fitness recovery. Our results suggest that such interactions constrain evolutionary rescue and add complexity to predictions of the responses of animal populations to climate change. The authors investigate temperature and pH effects on fitness of an abundant marine crustacean (copepod) across 25 generations. Reduced fitness under combined warming and acidification was recovered rapidly, but incompletely, due to interactions between warming and acidification effects.

Adaptive evolution and phenotypic plasticity will fuel resilience in the geologically unprecedented warming and acidification of the earth's oceans, however, we have much to learn about the interactions and costs of these mechanisms of resilience. Here, using 20 generations of experimental evolution followed by three generations of reciprocal transplants, we investigated the relationship between adaptation and plasticity in the marine copepod, Acartia tonsa, in future global change conditions (high temperature and high CO

The ability of consumers to convert ingested carbon into growth is critical for secondary production and trophic transfer. We conducted laboratory experiments to investigate the effect of different prey and concentration on the ingestion rate (IR), egg production rate (EPR) and egg production efficiency (EPE) of the ubiquitous copepod, Acartia tonsa. Experiments were run at several prey concentrations, ranging from 11 to 1132 μgC L–1, of the diatom Thalassiosira weissflogii, the autotrophic dinoflagellate Prorocentrum minimum, the heterotrophic dinoflagellate Oxyrrhis sp., the flagellate Dunaliella tertiolecta, and the bacterivorous scuticociliate Uronema sp. IR increased curvilinearly with concentration for all diets. EPR also increased curvilinearly with increasing food concentration similar to IR, with the exception of the flagellate diet, for which EPR decreased linearly with food concentration. EPR ranked as T. weissflogii > P. minimum > Oxyrrhis sp. = Uronema sp. > D. tertiolecta. IR and EPR were linearly related, except for flagellate diet. The slope of the carbon-based relationship between IR and EPR, the egg production efficiency (EPE), was highest for the diatom (77.5%) and lowest for the scuticociliate (4.2%). Egg production was not correlated to ingestion of the flagellate offered to A. tonsa. We conclude that of the five prey species, the diatom T. weissflogii is the best prey to promote A. tonsa reproduction, to optimize trophic transfer efficiency, and to increase mass cultivation of this species.

Time-series measurements of methylmercury (MeHg) concentrations in short-lived planktic animals, such as copepods, could allow for an evaluation of mercury (Hg) inputs and transferability to organisms in marine environments. If reliable, MeHg measurements in formalin-preserved marine animals could offer insights into past environmental MeHg levels. In the present study, we examined whether the amount of MeHg changed over time in formalin-preserved copepods for two species, Acartia tonsa, and Temora longicornis. Over a 51 (A. tonsa) and 7 (T. longicornis) week incubation, we found significant changes in MeHg content in both copepods, while the timing of these changes differed between species. Furthermore, we investigated the mechanism behind these temporal changes through a separate incubation experiment of formalin spiked with two levels of organic matter (OM), and stable-isotope-enriched Hg tracers. We found that the methylation of an inorganic 199Hg tracer was significantly higher in OM-enriched solutions in comparison to a control seawater-formalin solution. Our results suggest that formalin-preserved copepods are not fit for studies of past trends due to ongoing and unpredictable abiotic transformations of Hg in chemically preserved animal tissue.

Adaptive evolution from standing genetic variation and physiological plasticity will fuel resilience in the geologically unprecedented warming and acidification of the earth’s oceans. For marine animals, however, we have much to learn about the mechanisms, interactions, and costs of adaptation. Here, using 20 generations of experimental evolution followed by three generations of reciprocal transplantation, we investigate the relationship between adaptation and plasticity in the marine copepod, Acartia tonsa, in future greenhouse conditions (high temperature, high CO2). We find highly parallel genetic adaptation to greenhouse conditions in genes related to stress response, gene expression regulation, actin regulation, developmental processes, and energy production. However, reciprocal transplantation showed that genetic adaptation resulted in a loss of transcriptional plasticity, reduced fecundity, and reduced population growth when greenhouse animals were returned to ambient conditions or reared in low food conditions, suggestive of genetic assimilation after 20 generations of adaptation. Despite the loss of plasticity at F21, after three successive transplant generations, greenhouse-adapted animals were able to match the ambient-adaptive transcriptional profile. Concurrent changes in allele frequencies and erosion of nucleotide diversity suggest that this recovery occurred via adaptation back to ancestral conditions. These results demonstrate the power of experimental evolution from natural populations to reveal the mechanisms, timescales of responses, consequences, and reversibility of complex, physiological adaptation. While plasticity facilitated initial survival in global change conditions, it eroded after 20 generations as populations genetically adapted, limiting resilience to new stressors and previously benign environments.

Differences in population vulnerability to warming are defined by spatial patterns in thermal adaptation. These patterns may be driven by natural selection over spatial environmental gradients, but can also be shaped by gene flow, especially in marine taxa with high dispersal potential. Understanding and predicting organismal responses to warming requires disentangling the opposing effects of selection and gene flow. We begin by documenting genetic divergence of thermal tolerance and developmental phenotypic plasticity. Ten populations of the widespread copepod Acartia tonsa were collected from sites across a large thermal gradient, ranging from the Florida Keys to Northern New Brunswick, Canada (spanning over 20° latitude). Thermal performance curves (TPCs) from common garden experiments revealed local adaptation at the sampling range extremes, with thermal tolerance increasing at low latitudes and decreasing at high latitudes. The opposite pattern was observed in phenotypic plasticity, which was strongest at high latitudes. No relationship was observed between phenotypic plasticity and environmental variables. Instead, the results are consistent with the hypothesis of a trade-off between thermal tolerance and the strength of phenotypic plasticity. Over a large portion of the sampled range, however, we observed a remarkable lack of differentiation of TPCs. To examine whether this lack of divergence is the result of selection for a generalist performance curve or constraint by gene flow, we analyzed cytochrome oxidase I mtDNA sequences, which revealed four distinct genetic clades, abundant genetic diversity, and widely distributed haplotypes. Strong divergence in thermal performance within genetic clades, however, suggests that the pace of thermal adaptation can be relatively rapid. The combined insight from the laboratory physiological experiments and genetic data indicate that gene flow constrains differentiation of TPCs. This balance between gene flow and selection has implications for patterns of vulnerability to warming. Taking both genetic differentiation and phenotypic plasticity into account, our results suggest that local adaptation does not increase vulnerability to warming, and that low-latitude populations in general may be more vulnerable to predicted temperature change over the next century.

The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO 2 ) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO 2 ). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.

We hindcast a 110 year period (1860-1970) of morphodynamic behavior of the Western Scheldt estuary by means of a 2-D, high-resolution, process-based model and compare results to a historically unique bathymetric data set. Initially, the model skill decreases for a few decades. Against common perception, the model skill increases after that to become excellent after 110 years. We attribute this to the self-organization of the morphological system which is reproduced correctly by the numerical model. On time scales exceeding decades, the interaction between the major tidal forcing and the confinement of the estuary overrules other uncertainties. Both measured and modeled bathymetries reflect a trend of decreasing energy dissipation, less morphodynamic activity, and thus a more stable morphology over time, albeit that the estuarine adaptation time is long (approximately centuries). Process-based models applied in confined environments and under constant forcing conditions may perform well especially on long (greater than decades) time scales.

Induced prey defences against consumers are conspicuous in microbes, plants and animals. In toxigenic prey, a defence fitness cost should result in a trade-off between defence expression and individual growth. Yet, previous experimental work has failed to detect such induced defence cost in toxigenic phytoplankton. We measured a potential direct fitness cost of grazer-induced toxin production in a red tide dinoflagellate prey using relative gene expression (RGE) of a mitotic cyclin gene (cyc), a marker that correlates to cell growth. This approach disentangles the reduction in cell growth from the defence cost from the mortality by consumers. Treatments where the dinoflagellateAlexandrium catenellawere exposed to copepod grazers significantly increased toxin production while decreasing RGE ofcyc, indicating a defence-growth trade-off. The defence fitness cost represents a mean decrease of the cell growth rate of 32%. Simultaneously, we estimate that the traditional method to measure mortality loss by consumers is overestimated by 29%. The defence appears adaptive as the prey population persists in quasi steady state after the defence is induced. Our approach provides a novel framework to incorporate the fitness cost of defence in toxigenic prey–consumer interaction models.

Long-term environmental records are among the most valuable assets for understanding the trajectory and consequences of climate change. Here we report on a newly recovered time-series from Project Oceanology, a non-profit ocean science organization serving New England schools (USA) since 1972. As part of its educational mission, Project Oceanology has routinely and consistently recorded water temperature, pH, and oxygen as well as invertebrate and fish abundance in nearshore waters of the Thames River estuary in eastern Long Island Sound (LIS). We digitized these long-term records to test for decadal trends in abiotic and biotic variables including shifts in species abundance, richness, and diversity. Consistent with previous studies, the data revealed an above-average warming rate of eastern LIS waters over the past four decades (+0.45 °C decade−1), a non-linear acidification trend twice the global average (−0.04 pH units decade−1), and a notable decline in whole water-column dissolved oxygen concentrations (−0.29 mg L−1 decade−1). Trawl catches between 1997 and 2016 suggested a significant decrease in overall species diversity and richness, declines in cold-water adapted species such as American lobster (Homarus americanus), rock crab (Cancer irroratus), and winter flounder (Pseudopleuronectes americanus), but concurrent increases in the warm-water decapod Libinia emarginata (spider crab). Our study confirmed that Long Island Sound is a rapidly changing urban estuary, while demonstrating the value of long-term observations made by citizen-scientists, educators, and other stakeholders.

Inclusion and exclusion criteria of the PERISCOPE II trial. List of all in and exclusion criteria. (DOCX 19 kb)

In addition to being an esteemed marine ecologist and oceanographer, William T. (Bill) Peterson was a dedicated public servant, a leader in the ocean science community, and a mentor to a generation of scientists. Bill recognized the importance of applied science and the need for integrated “big science” programs to advance our understanding of ecosystems and to guide their management. As the first US GLOBEC program manager, he was pivotal in transitioning the concept of understanding how climate change impacts marine ecosystems to an operational national research program. The scientific insight and knowledge generated by US GLOBEC informed and advanced the ecosystem-based management approaches now being implemented for fishery management in the US. Bill held significant leadership roles in numerous international efforts to understand global and regional ecological processes, and organized and chaired a number of influential scientific conferences and their proceedings. He was passionate about working with and training young researchers. Bill’s academic affiliations, notably at Stony Brook and Oregon State Universities, enabled him to advise, train, and mentor a host of students, post-doctoral researchers, and laboratory technicians. Under his collegial guidance they became critical independent thinkers and diligent investigators. His former students and colleagues carry on Bill Peterson’s legacy of research that helps us understand marine ecosystems and informs more effective resource stewardship and conservation.

Predicting the response of populations to climate change requires an understanding of how various factors affect thermal performance. Genetic differentiation is well known to affect thermal performance, but the effects of sex and developmental phenotypic plasticity often go uncharacterized. We used common garden experiments to test for effects of local adaptation, developmental phenotypic plasticity and individual sex on thermal performance of the ubiquitous copepod, Acartia tonsa (Calanoida, Crustacea) from two populations strongly differing in thermal regimes (Florida and Connecticut, USA). Females had higher thermal tolerance than males in both populations, while the Florida population had higher thermal tolerance compared with the Connecticut population. An effect of developmental phenotypic plasticity on thermal tolerance was observed only in the Connecticut population. Our results show clearly that thermal performance is affected by complex interactions of the three tested variables. Ignoring sex-specific differences in thermal performance may result in a severe underestimation of population-level impacts of warming because of population decline due to sperm limitation. Furthermore, despite having a higher thermal tolerance, low-latitude populations may be more vulnerable to warming as they lack the ability to respond to increases in temperature through phenotypic plasticity.

Dinoflagellate paralytic shellfish toxin (PST) production is mediated by several abiotic and biotic factors. This study compared the relative importance of nitrogen source and concentration, prey alarm cues and grazer presence on toxin production of the marine dinoflagellate Alexandrium catenella (Group I, strain BF-5). In separate assays run under either nutrient-replete (F/2 medium) or nutrient-depleted (filtered seawater) conditions, PST production of A. catenella was measured as a function of varying concentrations of added nitrogen sources (ammonium and urea), alarm cues from lysed conspecific (A. catenella Group I strains) and interspecific (the diatom, Thalassiosira weissflogii, and the green flagellate, Tetraselmis sp.) algae, and the presence of a grazer (the copepod Acartia hudsonica). Results showed that addition of ammonium or urea did not increase PST production. Unexpectedly, interspecific alarm cues increased toxin production but conspecific ones did not. Grazer presence dramatically induced PST production in A. catenella, irrespective of nutrient conditions, and this effect was an order of magnitude greater than any of the other variables tested. These results corroborate previous studies on grazer-induced PST production, and support the hypothesis that grazer-induced toxin production is not an experimental artifact, but rather a prey defense mechanism.

Predicting the response of populations to climate change requires knowledge of thermal performance. Genetic differentiation and phenotypic plasticity affect thermal performance, but the effects of sex and developmental temperatures often go uncharacterized. We used common garden experiments to test for effects of local adaptation, developmental phenotypic plasticity, and individual sex on thermal performance of the ubiquitous copepod, Acartia tonsa. Females had higher thermal tolerance than males in both populations, while the Florida population had higher thermal tolerance compared to the Connecticut population. An effect of developmental phenotypic plasticity on thermal tolerance was observed only in the Connecticut population. Ignoring sex-specific differences may result in a severe underestimation of population-level impacts of warming (i.e. - population decline due to sperm limitation). Further, despite having a higher thermal tolerance, southern populations may be more vulnerable to warming as they lack the ability to respond to increases in temperature through phenotypic plasticity.

Summary Good analogues are keys for better understanding petroleum systems in frontier basins and new plays in proven basins. Recent discoveries have proven Permian carbonate plays (e.g. 7120/1–3 and 7220/11-1) in the Norwegian Barents Sea and Triassic siliciclastic plays (e.g. Goliat, Tornerose and Alke Sor) in the North Atlantic. Permian and Triassic plays have been unsuccessfully tested on the Mid-Norwegian continental shelf (M-NCS), but these plays have recently attracted renewed attention. However, the lack of offshore core data from this interval provides a major obstacle in developing valid play models. On the conjugate East and Northeast Greenland margin, excellent outcrops and a large number of shallow fully cored boreholes document the syn- to post-rift Permian–Triassic interval. Data from this interval in East and Northeast Greenland thus provide important constrains on key elements for new play models on the M-NCS. The presentation will provide observations from East and Northeast Greenland that may help to assist the definition of play models for the Permian–Triassic succession in the M-NCS and place them in a tectono-stratigraphic context.

Copepods, the most abundant metazoans in the oceans, exhibit sexual selection through mate choice. Mate choice may depend on resource and mate availability, mate quality, and the ability of an individual to assess potential mates. We measured the relative strength of mate choice for body size in male and female individuals of the copepod species Acartia tonsa and Acartia hudsonica as a function of food availability, encounter time, and previous social experience with the same and opposite sex. Mate choice in A. tonsa females depended on food availability and previous exposure to the opposite sex, whereas exposure to the opposite sex and encounter time affected mate choice in males. For A. hudsonica, previous social experience with the same and opposite sexes and encounter times were important for mate choice in females, and food availability and encounter time affected mate choice in males. The results suggest that mate choice responds to resource and mate availability, as well as social experience, but that the responses are species and sex-specific even within the same genus. Therefore, these copepods appear to have a flexible mate-sampling strategy that allows them to raise or lower their mate preferences in order to balance the benefits and costs associated with finding a desired mate.

The saxitoxins (STX), a group of potent neurotoxins produced by some marine algae (dinoflagellates and cyanobacteria), block voltage-gated sodium channels, inhibiting nerve-signal transmission in consumers of STX-bearing prey. Populations of grazers (clams and copepods) persistently exposed to the STX-bearing dinoflagellate Alexandrium fundyense are less susceptible to STX than naive ones. Adaptation to STX in clams is linked to a point mutation at the STX-binding site in the sodium channel, which dramatically lowers the sensitivity to the toxin (STX resistance). The present study tested if a similar mechanism of STX resistance occurs in the copepod Acartia hudsonica. Our cloning and sequencing results indicate that two full-length cDNA variants (AhNaV1 and AhNaV2) of the sodium channel exist in A. hudsonica, which result from alternative splicing of the single coding gene. Both variants have identical nucleotide sequences except that AhNav1 (the putative mutant isoform) contains a three-amino-acid (GRD) insertion and a single adjacent aa-substitution (A to V) close to the inactivation gate on the cytoplasmic linker between domains III and IV of the sodium channel. All individuals express both AhNaV1 and AhNaV2 in varying proportions. The functional consequences of the mutation were studied by inserting the three-amino acid codons into a rat (rNav1.2) sodium channel expressed in both Xenopus oocytes and HEK cells. Currents carried by construct rNav1.2 bearing the GRD insertion did not inactivate as completely, and recovered faster from inactivation than rNav1.2. These two rNav1.2 constructs were, however, equally sensitive to STX, suggesting that the GRD variation does not confer STX resistance on the rat sequence of Nav1.2. These results render unlikely the hypothesis that this novel mutation is responsible for the adaptation (via resistance) of A. hudsonica to STX-bearing prey.

A B S T R A C T The present study surveyed grazer-induced stimulation of paralytic shellfish toxin (PST) production by the marine dinoflagellate Alexandrium fundyense. The survey included species, known to graze upon A. fundyense, from five phyla: the protists, Polykrikos kofoidii (Dinoflagellata) and Tiarina fusus (Ciliophora), the bivalve molluscs Mytilus edulis and Mya arenaria (Mollusca), the ascidians, Molgula manhattensis and Botrylloides violaceus (Chordata), and the copepod, Eurytemora herdmani (Arthropoda). Direct (grazers in contact with cells of A. fundyense) and indirect (grazers not in contact with cells of A. fundyense) induction assays were carried out with protists and copepods. Only indirect assays were carried out with molluscs and ascidians. Indirect assays also tested whether induction of PST production occurred via kairomones or feeding-related cues. All metazoan grazers induced PST production. By contrast, neither of the two species of protistan grazer induced PST production. Direct and indirect inductions of PST production were evident for the copepod, with direct induction being significantly higher than indirect induction. Effects upon PST production by phylum, species (nested within phylum), and interactions of phylum by diet, and species by diet, were evident. When induction of PST production occurred, a kairomone effect was apparent, except for M. edulis. Similarly, feeding-related cues were evident, except for E. herdmani. An asymptotic relationship between the magnitude of indirect induction of PST production and total cell ingestion by the grazers suggests a saturation response of grazer-induced PST production.

SPIRIT checklist for the RePST trial, indicating which manuscript page contains each element of the study protocol. (DOX 135 kb)

To test the hypothesis that the sex ratio of the copepod Acartia tonsa is biased at birth, adult sex ratios of the offspring of families (21 families in 2011 and 72 in 2013) produced by field-caught females were determined in the laboratory under controlled conditions. Sex ratios at birth were estimated from the adult sex ratio, and after applying a correction in which all dead/missing individuals were counted as the rarer sex (males). Before correction the overall population sex ratio was female biased during both years, with over 42% of mothers producing clutches that were significantly different from unity. After correction, 25% (2013) to 33% (2011) of mothers still produced significantly biased sex ratios. The ratio of deaths of males to females had to be 1.75 to 1 (2011) and 7.25 to 1 (2013) for sex ratios not to be biased at birth. There was no evidence of sex reversal in any individual from juvenile (C4 stage) to adult, implying that juvenile sex ratios were also significantly biased. Hence, neither sex reversal nor differential mortality of the sexes is a likely explanation for the observed skewed sex ratios. The sex ratios at birth varied widely from the expectation from Mendelian inheritance of sex chromosomes, suggesting that another mechanism is responsible for skewed sex ratios at birth. Since the majority of families with biased sex ratios at birth were female dominated as adults, biased sex ratio at birth may contribute to the skewed sex ratio of adults observed in the field.

Lifetime spermatophore (sperm packet) production, which can provide valuable information about male energetics and mating, is not known for any species of copepod. Spermatophore production could limit reproduction in species in which females require multiple matings to remain fertilized and in populations that often have adult sex ratios highly skewed toward females. Spermatophore production rates were measured in the laboratory for two species of calanoid copepods, Acartia tonsa and Acartia hudsonica, from time of maturation until death, and under three food regimes (high, low, and no food). Rates of spermatophore production in A. tonsa were independent of food treatment. By contrast, in A. hudsonica, spermatophore production was significantly greater under high food than in low or no food. Spermatophore production decreased significantly with age in both species and the majority of males ceased producing spermatophores halfway through their adult lives. This pattern occurred regardless of food treatment, except for in A. hudsonica under low-food conditions: low production rates in younger males were compensated by continued reproduction into old age. Therefore, there was no difference in the total lifetime number of spermatophores produced by males of A. hudsonica fed at high- or low-food conditions. In the absence of food, however, significantly fewer spermatophores were produced. In A. tonsa, there was no difference among food treatments in the total number of spermatophores produced over a male’s life. The effect of these low rates of spermatophore production on fertilization was evident in the field. During 2 years of weekly collections, at no point in time were all females in the population fertilized. We conclude that low rates of spermatophore production over a lifetime and the short reproductive period of males contribute to the low frequencies of mated females in field populations.

The dinoflagellate, Alexandrium fundyense, produces paralytic shellfish toxins and co-occurs with populations of the copepod, Acartia hudsonica, from Maine, but not New Jersey. The hypothesis that history of co-occurrence between predator and prey effects the ability of prey to recognize and respond to predators with increased toxin production was tested for this copepod-alga interaction. When A. fundyense was exposed to waterborne cues released by copepods from Maine (indirect exposure) that were either starved or fed toxic cells, cell toxin quota increased by 35% compared to unexposed controls. The induced response was significantly less for cells exposed to waterborne cues of copepods from New Jersey, and induction (20%) was only elicited by this population when fed toxic cells. These results suggest that A. fundyense responded to a kairomone from copepods from Maine, but required a feeding cue from copepods from New Jersey. An increase of approximately 300% in cell toxin quota, however, occurred when cells were directly exposed to grazing, and was independent of copepod population. Evolutionary history, therefore, had no apparent effect when induction was underlain by feeding cues. In assays with a mixture of toxic and nontoxic cells, selection for the latter was evident, and also independent of copepod population. Selectivity for nontoxic cells, however, could not account for changes in cell toxin content in the mixture experiments. When A. fundyense was exposed to extracts of toxic or nontoxic Alexandrium, toxin production increased significantly (23%), suggesting modest induction by an alga-to-alga alarm signal.

Mating in many copepod species is not random; moreover, individuals have preferences for certain qualities in their mates. This study tested whether female mating status (virgin versus mated) affects mate choice in males in the copepod species Acartia tonsa and Acartia hudsonica, both in laboratory and field populations. In addition, the costs and benefits associated with mating twice versus once for females of both species were tested in laboratory studies. In both A. tonsa and Acartia hudsonica, males mated more frequently with virgin females compared with females that had already mated, suggesting that female reproductive status is important for mating and mate choice. Frequencies of females carrying double spermatophores in the field (at three sites and seasonally within a site) were consistently low, implying that mate choice for female reproductive status is present in natural populations as well. In Acartia hudsonica, the frequency of females carrying double spermatophores was positively related to spermatophore volume and male and female sizes, but negatively related to temperature. No such relationships were found for A. tonsa. However, the frequency of females carrying double spermatophores decreased as the season progressed. In both copepod species, there was no difference in the number of nauplii produced, length of fertilization or lifespan between females that had mated twice compared with those that had mated only once. Hence, there was no particular cost or benefit to mating a second time. Our findings suggest that female reproductive status is important for mating success in these two coastal copepod species and that this is most likely due to male mate-choice.

Local adaptation of the copepod Acartia hudsonica to toxic Alexandrium spp. is associated with degree of historical co-exposure. Recently, a novel mutation in the sodium channel in A. hudsonica was hypothesized to be the mechanism of adaptation to toxic Alexandrium; all copepods express both types of sodium channels. We tested the hypothesis that mutant sodium channel expression in A. hudsonica individuals corresponded to historical co-exposure to A. fundyense. Female A. hudsonica were sampled from historically exposed (Maine) and naive (Connecticut and New Jersey) populations to A. fundyense, throughout the 2011 season of growth of A. hudsonica. There were no consistent differences in wild-type: mutant isoform ratios nor in the relative abundance of individuals that predominately express one type of isoform, either through time within a population or among populations or over time within each location. We also tested the hypothesis that expression of the mutant sodium channel isoform in A. hudsonica should increase during the progression of a toxic Alexandrium bloom. Sodium channel expression was compared before, during, and after the 2011 toxic Alexandrium spp. bloom in Northport Harbor, NY. Moreover, the relative expression of the mutant isoform increased slightly after the peak of the toxic Alexandrium spp. bloom; however, there was no simultaneous increase in individuals that predominately express mutant channel isoforms. Overall, there was little evidence in support of our hypotheses. Other mechanisms must be responsible for the observed geographic differences in adaptation of copepods to toxic Alexandrium.

Some species in the dinoflagellate genus Alexandrium spp. produce a suite of neurotoxins that block sodium channels, known as paralytic shellfish toxins (PST), which have deleterious effects on grazers. Populations of the ubiquitous copepod grazer Acartia hudsonica that have co-occurred with toxic Alexandrium spp. are better adapted than naive populations. The mechanism of adaptation is currently unknown. We hypothesized that a mutation in the sodium channel could account for the grazer adaptation. We tested two hypotheses: (1) Expression of the mutant sodium channel could be induced by exposure to toxic Alexandrium fundyense; (2) in the absence of induction, selection exerted by toxic A. fundyense would favor copepods that predominantly express the mutant isoform. In the copepod A. hudsonica, both isoforms are expressed in all individuals in varying proportions. Thus, in addition to comparing expression ratios of wild-type to mutant isoforms for individual copepods, we also partitioned copepods into three groups: those that predominantly express the mutant (PMI) isoform, the wild-type (PWI) isoform, or both isoforms approximately equally (EI). There were no differences in isoform expression between individuals that were fed toxic and nontoxic food after three and 6 days; induction of mutant isoform expression did not occur. Furthermore, the hypothesis that mutant isoform expression responds to toxic food was also rejected. That is, no consistent evidence showed that the wild-type to mutant isoform ratios decreased, or that the relative proportion of PMI individuals increased, due to the consumption of toxic food over four generations. However, in the selected line that was continuously exposed to toxic food sources, egg production rate increased, which suggested that adaptation occurred but was unrelated to sodium channel isoform expression.

In coastal ecosystems with decades of eutrophication and other anthropogenic stressors, the impact of climate change on planktonic communities can be difficult to detect. A time series of monthly water temperatures in the Central Basin of Long Island Sound (LIS) from the late 1940s until 2012 indicates a warming rate of 0.03 °C year−1. Relative to the early 1950s, there has been a concurrent decrease in the mean size of the dominant copepod species Acartia tonsa and Acartia hudsonica, an increase in the proportion of the small copepod Oithona sp., and the disappearance of the two largest-sized copepod genera from the 1950s. These changes are consistent with predictions of the impact of climate change on aquatic ectotherms. This suggests that even in eutrophic systems where food is not limiting, a continued increase in temperature could result in a smaller-sized copepod community. Since copepods dominate the zooplankton, which in turn link primary producers and upper trophic levels, a reduction in mean size could alter food web connectivity, decreasing the efficiency of trophic transfer between phytoplankton and endemic larval fish.

The effects of the colonial peritrich ciliate epibiont, Zoothamnium sp., on fitness components of the copepod Acartia tonsa were examined during a three-week infestation event in Long Island Sound. Infestation rate and intensity (ciliate load copepod 21 ), copepod body size and mating success were measured on six separate occasions in the field. Infestation rates exceeded 60% in both male and female copepods. Infested females had a significantly greater ciliate load than males on three of the six sampling dates. Infested males were significantly smaller than uninfested males midway through the event, whereas infested females were significantly smaller during the peak in infestation rate and intensity. There was no difference in the frequency of unmated females between infested and uninfested individuals on any sampling date. Laboratory experiments were carried out under three food regimes (starvation, food-limited and food-unlimited). Survivorship was significantly lower for infested versus uninfested males under starvation, but not under the food-unlimited condition. Infested females, however, showed significantly lower survivorship than uninfested ones under all three food regimes. In addition, infested females produced significantly fewer eggs than uninfested females under starvation and food-unlimited conditions. Overall, both male and female A. tonsa bearing the ciliate epibiont Zoothamnium experience a significant decrease in components of fitness.

article i nfo Article history: We define tolerance to starvation as the ability to survive in the absence of food. We tested the hypotheses that adult male Acartia tonsa copepods are less tolerant to starvation than adult female copepods, and that tolerance to starvation is affected by prior diet, age of individuals and duration spent in the adult stage. We also tested whether, during the period of starvation, egg production affected tolerance to starvation in fe- male adults. Field-collected male and female copepods were fed non-limiting rations of the toxic dinoflagel- late Alexandrium fundyense, non-toxic Alexandrium tamarense, the nutritionally insufficient dinoflagellate Prorocentrum minimum, or a standard non-toxic diet (a mixture of the diatom Thalassiosira weissflogii, the flagellate Tetraselmis sp., and the green microalga Isochrysis galbana) for 24 h before starvation. In separate experiments, male and female field-caught copepods were either starved or fed non-limiting rations of the standard non-toxic diet. Finally, tolerance to starvation was measured in adults raised in laboratory cohorts. Tolerance to starvation was lower for adult males than females in all experiments, with all starved copepods dying within fifteen days. We observed a similar pattern for field-caught and laboratory-raised animals: dif- ferences in adult survivorship between the sexes were immediately apparent under starvation. In contrast, adult survivorship in fed animals was relatively constant and independent of sex during the first fifteen days. Subsequently, male survivorship was lower. In the laboratory-cohort experiments differences in toler- ance to starvation between the sexes were not affected by age or by duration within the adult stage. Taken together, the results of this study suggest that adult male A. tonsa are physiologically less tolerant to starva- tion compared to females, and may explain observations of female-skewed adult sex-ratios in food-limited field and laboratory experiments. Further, total egg production and survivorship during starvation were uncorrelated. We suggest that the former is controlled by previous feeding history and the latter by basal metabolism.

article i nfo An efficient RNA-extraction method is crucial for transcriptomic studies of ecologically important organisms like copepods. In this study, we used the copepod Acartia hudsonica as a test species to evaluate existing methods, and formulated several improved protocols to consistently and efficiently isolate high-quality RNA from both pooled and individual copepod samples. Our protocols recommend copepod preservation in a phenol/guanidine thiocyanate reagent, followed by bead-beating or micropestle homogenization. To obtain high-quality RNA from pooled samples, one initial chloroform extraction followed by multiple phenol/chloroform extractions are needed before the raw RNA samples are further purified with the Qiagen RNeasy Mini Kit. When analyzing individual samples, one chloroform extraction followed by purification using the Zymo Research Direct-zol™MiniPrep Kit gives the best results. Using these protocols, we isolated RNA from pooled and individual A. hudsonica samples with consistent recovery rate (individual samples: 95 ± 12 ng/male; 272 ± 57 ng/female). The cDNAs synthesized using these RNAs were proven to be of high quality by successful ampli fication of tran- scripts including the >7 kb alpha subunit of the voltage-gated sodium channel gene (SCG). For individual A. hudsonica samples, our protocols yielded significantlyhigher success rates(95%,n = 456) in reverse transcription quantitative PCR of SCG compared to existing methods (0-85%, n = 150). Applications of these protocols to nine other copepod species from seven families have led us to achieve high-quality RNAs and cDNAs from pooled and/ or individual samples. As a result of testing the protocols, we obtained cDNA sequences of various genes in ten co- pepod species, some of which are the first record in copepods. Our protocols can easily be adopted by laboratories to facilitate molecular work on copepods.