CARSTEN GRUPSTRA
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Coral-eating fish (corallivores) may aid coral reef resilience through the dispersal of millions of live Symbiodiniaceae (coral symbionts) cells in their feces. This figure lists the concentrations of Symbiodiniaceae cells in distinct environmental compartments on coral reefs, based on my work in Mo'orea and other published literature (Grupstra et al. 2021). Artwork by Janavi Mahimtura Folmsbee.
Virtually all animals rely on microbiomes to support their health and fitness. My research addresses fundamental questions pertaining to the nature of this relationship: How are microbiomes assembled and how do they influence the function and survival of their hosts? To answer these questions, I study tropical corals; animals that rely on dinoflagellates (family Symbiodiniaceae) for food supply, and diverse other microorganisms (including archaea, bacteria, fungi and viruses) that provide other services. 

​I aim to build an understanding of how interactions between animals and microorganisms contribute to ecosystem resilience. I mostly work at the National Science Foundation (NSF)-funded Long Term Ecological Research (LTER) site in Mo'orea, French Polynesia. 
A video explaining how coral predators contribute to the dispersal of key coral symbionts (Grupstra et al. 2021).

Current projects
Dispersal of microbial symbionts by predators​
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A speckled butterflyfish (Chaetodon citrinellus) browsing in a stand of branching coral (Acropora muricata)

​​For part of my dissertation work, I am characterizing the dispersal of symbiotic microorganisms by coral predators (corallivores) such as butterflyfishes and parrotfishes. Specifically, I am quantifying the density and diversity of coral photosymbionts in the feces of corallivorous fish. By combining this with data on corallivore defecation behavior, I am able to quantify the exact contribution of corallivores to symbiont dispersal. Learn more here. 
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Cultures of coral photosymbionts isolated from fecal samples of coral predators.
Dynamics of RNA viruses infecting eukaryotic symbionts 
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A snorkler from OSU samples a colony of Porites lobata so that we can characterize its community of viruses

​One of my dissertation chapters focuses on describing the dynamics of RNA viruses infecting photosymbiont communities associated with corals. I am combining tank experiments with large-scale repeated sampling of coral colonies to identify how RNA virus communities are linked to coral health and resilience to stress. By studying RNA virus communities across species of coral, I aim to increase our understanding of the role of viruses in shaping host phenotypes. Read more here.
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Viral pellets from environmental samples acquired using centrifugation with Polyethylene glycol
Community structure of animal-associated microorganisms 
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A coral species (Oculina patagonica) that is invasive in the relatively cold waters Along the Mediterranean coast of Spain

​​​I am interested in how communities of prokaryotic and eukaryotic microrganisms can help animal hosts acclimatize to changing environments. By combining tank-based experiments with in-situ transplantation experiments and sampling across natural or man-made environmental gradients, I aim to elucidate how patterns of microbial community structure contribute to host health and decline. Learn more about this work here and here.
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A schematic illustrating a reciprocal transplantation experiment with two coral species

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