When the Going Gets Tough, the Females Get Going: Sex-Specific Physiological Responses to Simultaneous Exposure to Hypoxia and Marine Heatwave Events in a Ubiquitous Copepod.

The existence of sex-specific differences in phenotypic traits is widely recognized. Yet they are often ignored in studies looking at the impact of global changes on marine organisms, particularly within the context of combined drivers that are known to elicit complex interactions. We tested sex-specific physiological responses of the cosmopolitan and ecologically important marine copepod Acartia tonsa exposed to combined hypoxia and marine heatwave (MHW) conditions, both of which individually strongly affect marine ectotherms. Females and males were acutely exposed for 5 days to a combination of either control (18°C) or a high temperature mimicking a MHW (25°C), and normoxia (100% O2 sat.) or mild hypoxia (35% O2 sat.). Life-history traits, as well as sex-specific survival and physiological traits, were measured. Females had overall higher thermal tolerance levels and responded differently than males when exposed to the combined global change drivers investigated. Females also showed lower metabolic thermal sensitivity when compared to males. Additionally, the MHW exerted a dominant effect on the traits investigated, causing a lower survival and higher metabolic rate at 25°C. However, egg production rates appeared unaffected by hypoxia and MHW conditions. Our results showed that MHWs could strongly affect copepods' survival, that combined exposure to hypoxia and MHW exerted an interactive effect only on CTmax, and that sex-specific vulnerability to these global change drivers could have major implications for population dynamics. Our results highlight the importance of considering the differences in the responses of females and males to rapid environmental changes to improve the implementation of climate-smart conservation approaches.

First evidence of lithium toxicity in the cryptic species complex of the estuarine copepod Eurytemora affinis.

The development of renewable and low-carbon energy sources means that strategic elements such as lithium (Li) are increasingly being used. The data available on the effects of Li on aquatic organisms are relatively scarce. The copepod Eurytemora affinis, widely distributed in the brackish estuarine waters of the northern hemisphere, is a species of choice in ecotoxicology but in fact constitutes a cryptic species complex, composed of at least six cryptic species. Cryptic diversity can lead to misinterpretation and alter the reproducibility of routine ecotoxicological tests. In the present study, two cryptic species of the E. affinis complex from the Seine (European clade) and the St. Lawrence (North-Atlantic clade) estuaries were used to assess Li toxicity and to compare their differential sensitivity. Larvae were exposed to different concentrations of Li (0.4, 4.39, 35.36 and 80.83 mg L-1) under semi-static conditions for 96 h. Larval development stages were determined and log-logistic functions were fitted to evaluate mortality (LC50) and growth (EC50) parameters. After 96 h of exposure, the results showed that the European and North-Atlantic clades had LC50 values of 55.33 and 67.81 mg L-1 and EC50 values of 28.94 and 41.45 mg L-1, respectively. A moderate difference in sensitivity to Li between the European and North-Atlantic clades of the E. affinis complex was observed. Thus, the cryptic species diversity should be considered using E. affinis to avoid bias in the interpretation of the data. Despite environmental concentrations of Li are expected to increase over the next years, EC50 and LC50 found for E. affinis cryptic species are largely higher than Li environmental concentrations to provoke extreme effects.

Living at depth: ecophysiological condition of Boreomysis arctica in autumn and winter in the St. Lawrence estuary and gulf.

Mysids, besides krill, play a significant role in energy transfer and carbon sequestration. The ecology of coastal species is better understood than that of deep dwelling species such as Boreomysis arctica. The objectives of this study were to quantify spatiotemporal variations in body condition and the trophic level of B. arctica in autumn and winter, under sea-ice conditions in the St. Lawrence system, using a multimarker approach. We sampled along a 1000 km transect. Mean abundances in winter were higher in the estuary compared to the Gulf of St. Lawrence. Body condition, measured as total lipid content, was higher in winter than in autumn. Lipids of B. arctica were mainly composed of wax esters, thereby B. arctica is richer in energetic lipids compared to the three dominant krill species. We also observed seasonal differences in the trophic level of B. arctica, revealing carnivorous behavior in autumn compared to omnivory in winter. High intra-specific variability in both energetic strategy and feeding behavior was found that is potentially due to opportunistic feeding. Energy rich reserves suggest that B. arctica could act as a valuable prey for both benthic and pelagic consumers and thus playing a key role in bentho-pelagic energy transfer.

A first glimpse of larval ecology of halibut species in the Gulf of St. Lawrence, Canada.

Knowledge of the larval ecology of winter-spawning fish from the Estuary and Gulf of St. Lawrence, Canada, remains scarce due to the seasonal ice cover that prevents ichthyoplankton sampling using conventional methods. Two winter-spawning species, Atlantic halibut (AH, Hippoglossus hippoglossus) and Greenland halibut (GH, Reinhardtius hippoglossoides), support the most important groundfish fisheries of this area. In March 2020, the authors captured 10 halibut larvae ranging in size from 5 to 14 mm during an opportunistic survey in the GSL onboard an icebreaking vessel. Of these, eight were AH and two GH. Judging by their very small size, the larvae were only a few days old, suggesting that the spawning grounds are close to the capture sites. This effort constitutes a first step in validating the putative spawning areas for these two important GSL stocks. This knowledge is important for the conservation and sustainable management of these fisheries.

Rare earth element uptake mechanisms in plankton in the Estuary and Gulf of St. Lawrence.

The global shift toward green energy alternatives escalates demands for new resources, including rare earth elements (REEs), as per their implications in various green innovations. However, our understanding of their environmental cycle, especially the interactions with aquatic organisms, remains deficient, ultimately hindering environmental protection efforts. Here, we investigate the accumulation of REEs and 18 other elements in bulk and sorted plankton collected with different net mesh sizes (30, 63, 200, 333, 500 µm) in the Estuary and Gulf of St. Lawrence in the summer and winter of 2020. We observed significant correlations between the concentrations of REEs and elements of different charge numbers and ionic radii (Ba, Co, Cs, Fe, Mn, Pb, Rb and V), indicating non-selective uptake of REEs into plankton. All these elements have their highest concentrations in the fluvial corridor and upper estuary, with more significant enrichment in phytoplankton ([La] = 26.4 ± 4.8 mg kg-1) than zooplankton ([La] = 11.6 ± 8.3 mg kg-1). Their concentrations decrease to the minimum in the Gulf of St. Lawrence, especially in zooplankton ([La] = 4.8 × 10-2 ± 3.2 × 10-2 mg kg-1). We also assessed REE patterns to identify differential REE fractionation processes and anomalies. The freshwater plankton exhibits enrichment of middle REEs (MREEs) relative to the light and heavy REEs (LREEs and HREEs), potentially because of the higher binding affinity of MREEs on cellular surface transporters and metal loading effects. In estuarine and marine settings, the REE patterns in biological samples align with suspended particles, exhibiting a linear trend with LREE enrichment. This process is more noticeable in sorted macrozooplankton, which have significant Eu anomalies (Eu/Eu* up to 2), indicating differential incorporation of REEs into the chitin shells. This study highlights the significant enrichment of REEs into freshwater primary producers and the accumulation pathway similar to other inorganic elements.

Genetic and morphological heterogeneity among populations of Eurytemora affinis (Crustacea: Copepoda: Temoridae) in European waters.

Our understanding of the systematics of the Eurytemora affinis complex developed at a fast pace over the last decades. Formerly considered as a complex of cryptic species, it is now believed to include three valid species: E. affinis, Eurytemora carolleeae, and Eurytemora caspica. American and European representatives have been studied in detail with respect to fine-scale geographic distribution, levels of genetic subdivision, evolutionary and demographic histories. Morphological components have been less explored. In this study, an analysis of the phylogeny and morphology of E. affinis was done, with a special focus on European populations. A total of 447 individuals of E. affinis from Europe were analyzed with genetic tools and 170 individuals according to morphological criteria. Common and new morphological and genetic features were analyzed. For this, we used ML and Bayesian methods to analyze the bar coding mt-DNA gene cytochrome c oxidase I subunit. Both genetic and morphological analyses showed high heterogeneities among the E. affinis populations from Europe. As a result, three local populations of E. affinis in Western Europe, including the European part of Russia, were established. Their genetic and morphological heterogeneity corresponded to the subspecies level.

Influence of intertidal recreational fisheries and 'bouchot' mussel culture on bivalve recruitment.

In coastal environments, fishing and aquaculture may be important sources of disturbance to ecosystem functioning, the quantification of which must be assessed to make them more sustainable. In the Chausey Archipelago, France, recreational fishing and commercial shellfish farming are the only two evident anthropogenic activities, dominated by bivalve hand-raking and 'bouchot' mussel culture, respectively. This study evaluates the impact of both activities on bivalve recruitment dynamics by comparing primary recruitment intensity (short-term effect) and recruitment efficiency (medium-term effect) by sampling bivalves in reference (undisturbed) and disturbed (i.e. subjected to hand-raking or in 'bouchot' mussel culture areas) parcels throughout and at the end of the recruitment season, respectively. Specific hypotheses evaluated were that (H1) bivalve hand-raking negatively affects bivalve recruitment and that (H2) 'bouchot' mussel culture promotes bivalve recruitment. Patterns in bivalve community structure in reference parcels (i.e. natural pattern) differed between initial and final recruitment, underlining the great importance of early post-settlement processes, particularly secondary dispersal. Primary recruitment intensity was inhibited in hand-raking parcels whereas it was promoted in 'bouchot' mussel culture parcels, but the effect on recruitment efficiency was muted for both activities due to post-settlement processes. Nevertheless, the importance of effects that occur during the first step of recruitment should not be ignored as they may affect bivalve communities and induce immediate consequences on the trophic web through a cascade effect. Finally, it is highlighted that hand-raking damages all life stages of the common cockle Cerastoderma edule, one of the major target species, suggesting that this activity should be managed with greater caution than is currently done.

Heterogeneity within the native range: population genetic analyses of sympatric invasive and noninvasive clades of the freshwater invading copepod Eurytemora affinis.

Invasive species are often composed of highly differentiated populations or sibling species distributed across their native ranges. This study analysed patterns of distribution and the evolutionary and demographic histories of populations within the native range of the copepod species complex Eurytemora affinis. Genetic structure was analysed for samples from 17 locations from both the invaded and native ranges in the St Lawrence River drainage basin, using 652 base pairs of the mitochondrial cytochrome oxidase subunit I gene. This study revealed a high degree of heterogeneity in genetic structure and habitat type in the native range, as well as a bias in the sources of invasive populations. Two genetically distinct clades showed a pattern of niche partitioning within the St Lawrence basin. The noninvasive North Atlantic clade primarily occupied the central portion of the St Lawrence Middle Estuary, whereas the invasive Atlantic clade was more prevalent along the margins, in the upstream reaches of the estuary and downstream salt marshes. Habitat partitioning and genetic subdivision was also present within the Atlantic clade. The freshwater populations were genetically more proximate to the Atlantic clade populations in the estuary than to those in the salt marsh, suggesting the estuary as the source of the invasive populations. The freshwater invading populations showed evidence of a modest population bottleneck. Populations from both clades showed genetic signatures of demographic population expansions that preceded the timing of the last glacial maximum, supporting the St Lawrence as a secondary contact zone between the two clades. Additional analyses on physiological and evolutionary properties of populations in the native range, along with analysis of the selection regime within native habitats, might yield insights into the evolutionary potential to invade.