Research in the Mercier Lab - Mercier Lab

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Research in the Mercier Lab

Research in the Mercier Lab examines the interactions between benthic organisms and environmental factors at various scales, typically combining field samplings and experimental trials with microscopic/cellular and biochemical analyses. Breakthroughs in biology, ecology, evolution and conservation made over the past several years were published in prominent journals and have received media coverage, including:
  1. first evidence of lunar rhythms in the reproduction of deep-water taxa;
  2. first direct evidence of allogeneic fusion (chimerism) in a unitary organism and in deuterostomes;
  3. first demonstration of a functional relationship between fish larvae and deep-sea corals;
  4. first demonstration of active buoyancy adjustment leading to rapid dispersal in so-called sedentary benthic animals;
  5. first evidence of anticipatory immune and hormonal responses to predation risk in an echinoderm.
Marine ecology and the control of biological functions in marine organisms
The core of the lab's research focuses on assessing the drivers of various processes (growth, gamete synthesis, larval development, settlement, dispersal) in macrobenthic organisms with complex (pelago-benthic) life histories. To achieve this, we typically amalgamate evidence obtained from the analysis of field samples and experimental studies, with an aim to compare congeners inhabiting seasonal and extreme environments (cold-temperate coasts vs deep sea vs poles). Our findings promise to help elucidate the respective roles played by exogenous factors (i.e. temperature, photoperiod, food, lunar cycles) and inter-individual exchanges (i.e. proximity/density, chemical communication) in the dispersal and persistence of species, of significance to both evolutionary biology and resources management.
Early work in the 1990s centered on the role of endogenous and exogenous cues in coordinating annual spawning events, and drew attention to chemical communication around the breeding season of echinoderms for the first time, of relevance to the maintenance of reproductive populations. More recently, our discovery of mass lunar spawnings in boreal species and of lunar components in the reproduction of deep-water taxa drew attention to overlooked proxies of lunar cues in cold-water environments and the disphotic zone (~200-1200 m). Over the past few years, further work evidenced environmentally-mediated breeding and growth in deep-water taxa, of special significance in view of predicted changes in the seasonal timing of life-history events caused by climate change (shift in phase relationship between photoperiod and temperature). Bathymetric shifts in maternal reproductive investment were shown. An entirely new area of research is being developed around Arctic macrobenthic communities, following a twofold reasoning. (1) The Arctic fits in the continuum we have studied so far, i.e. subarctic coasts and underlying deep ocean (representing marked and weakly seasonal environments, respectively), while offering new settings for testing hypotheses related to photoperiod (high latitude, periodic ice cover) and food availability (unique primary production) using the same or closely related taxa. (2) Marine species are expected to move into, or shift their distributions towards Arctic waters in the face of climate change, while exogenous pressures on this environment (e.g. ocean warming, ship traffic) increase, stressing the need to understand the life-history strategies of locally adapted species to predict impacts on biodiversity.

Dispersal and biology of early life stages
Our research in functional and evolutionary ecology led to the discovery of fusion among brooded offspring (embryos and larvae), which was the first direct evidence of chimerism in a unitary organism (media covered), and a driver of offspring size variations in live-bearing (vivparous) organisms. We then showed embryonic fusion for the first time in a broadcast-spawning deuterostome (a clade that groups chordates and echinoderms), expanding the significance of this strategy. Several studies on offspring phenotypes were published. We also led and co-authored papers on paradigms linking larval modes, pelagic duration and dispersal (key to population connectivity and marine conservation), and contributed to a recent review of larval dispersal in the deep sea. In 2019, a multi-HQP paper from our lab highlighted an overlooked locomotor behaviour in benthic taxa, challenging dispersal theories and tenets of fisheries management. It also stirred media interest (texts in National Geographic, The Economist, Quebec Science, etc., and several television and radio interviews in Canada and abroad).

Biology & conservation of ecologically and commercially valuable marine species
Applied research in our lab is broadly divided between the sustainable exploitation of commercial species and the coonservation of habitat-forming species.
1. The first segment includes global synthetic work on sea cucumber (biology, fisheries, auqaculture, trade), papers on their conservation and IUCN Red List assessments of 22 species. The basic and applied research conducted by my HQPs on the biology of sea cucumbers in Atlantic Canada is helping DFO manage the resource and stakeholders lay the foundation of an eventual aquaculture production. A PhD student developed the first direct aging method for sea cucumber, which is providing a first-of-its-kind tool for measuring size at age in this polymorphic taxon. We published a 24-chapter book on the leading commercial species in Asia (Apostichopus japonicus) and contributed to the publication of its genome. The CBC TV show Land & Sea filmed in our lab in fall 2019 to prepare a feature on sea cucumber research and present the fishing industry in Atlantic Canada. Also in 2019, the government and Indigenous communities of Nunavut reached out to our team for guidance on the exploitation and conservation of sea cucumbers and other echinoderms in various hamlets. In late 2020, our lab, with a group of current and former HQPs, published a full synthesis of knowledge on the Atantic sea cucumber Cucumaria frondosa. We are now preparing a full issue of the journal Advances in Marine Biology dedicated to the prime Indo-Pacific species Holothuria scabra. Finally, a 50-chapter book is coming up on the World of Sea Cucumbers - Challenges, Advances & Innovations; this one will provide a broad coverage of sea cucumber biology, ecology, fisheries, aquaculture and trade, while also bringing forward novel cultural, socioeconomic and scientific topics related to commercial and non-commercial species worldwide.
2. In deep-sea conservation matters, our discovery of the role of cold-water corals as essential fish habitat in 2012 was broadly covered by the media and is still having impacts today, directly and via derived work (e.g. World Wildlife Fund documents and DFO’s Coral & Sponge Conservation Strategy for Eastern Canada). Our deep-sea conservation work is still ongoing, as part of a concerted effort to guide DFO and NAFO in designing management measures for habitat-forming corals and sponges in Atlantic Canada (e.g. several Amundsen expeditions).

Species interactions and trophic ecology
Many of our postodcs and grad students have contributed to a better understanding of species interactions, feeding strategies and trophic ecology in cold-water and deep-sea taxa, including corals, sponges, echinoderms, pycnogonids, and broad bentho-pelagic assemblages. A student-led review and an analysis of deep-water food-web ecology studies that used stable isotope (δ15N, δ13C) and fatty acid trophic biomarkers was published in 2019; it revealed global trends and provided the first solid framework for moving forward in this quickly expanding field.

Health markers and the effects of pollution and climate change
An important segment of our research is dedicated to expanding our understanding of the response of marine animals to various types of stressors. Among others, we have investigated the effects of ocean acidification, oil pollution and hydrostatic pressure on various behavioural and physiological processes under realistic conditions (open flow-through mesocosms). We are also trying to develop cellular and hormonal/enzymatic biomarkers of stress in keystone and commercially valuable species facing environmental (salinity, turbidity, air exposure, temperature), biological (conspecific density, predation pressure) and anthropogenic (pollution) pressures. The most recent development in this research focus was the discovery that echinoderms could not only react to direct physical stressors, but also display anticipatory immune and hormonal responses in the face of impending threats, before they even materialized. The responses observed intersected with recently defined central emotional states and  they waned after prolonged stress in a manner akin to habituation, which are traits that have rarely been shown in non-vertebrates, and never in echinoderms. Because the latter sit alongside chordates in the deuterostome clade, such findings offer unique insights into the adaptive value and evolution of stress responses in animals. We are currently working to refine our knowledge of cellular immune responses in this phylum, and looking into their unique regenerative abilities.

Characterizing and safeguarding marine biodiversity
As underlined recently by the Census of Marine Life, there is currently an unimaginable number of undescribed or misidentified species, and this deficiency is curtailing studies that strive to draw comprehensive pictures of marine ecosystems. Discovering and properly describing the species that colonize our oceans is especially important in the face of impending biodiversity crises. While our lab's contribution remains infinitesimal in light of the pressing needs, we are particularly fond of collaborative studies that allow us to combine new/revised taxonomic records and broader information on the distribution and/or ecological role of given species. Since 2013, our group has published several papers of relevance to the taxonomy and distribution of marine species, including a new species of deep-sea holothuroid discovered during one of our sampling campaigns, several new records and range extensions for Canadian species, and various other notes on tropical species. In addition, we have contributed over 20 full-length publications on the status of sea cucumber species worldwide on behalf of the IUCN Red List of Threatened Species.

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