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1. Invertebrate herbivores influence seagrass wasting disease dynamics

   https://doi.org/10.1002/ecy.4493  

   Graham, Olivia J; Aoki, Lillian R; Burge, Colleen A; Harvell, C Drew (January 2025, Ecology)

   Abstract Although invertebrate herbivores commonly impact terrestrial plant diseases by facilitating transmission of plant pathogens and increasing host susceptibility to infection via wounding, less is known about the role of herbivores in marine plant disease dynamics. Importantly, transmission via herbivores may not be required in the ocean since saline ocean waters support pathogen survival and transmission. Through laboratory experiments with eelgrass (Zostera marina), we showed that isopods (Pentidotea wosnesenskii) and snails (Lacunaspp.) created grazing scars that increased disease severity and thus indirectly facilitated transmission ofLabyrinthula zosterae(Lz), a protist that causes seagrass wasting disease. Experiments also quantified different feeding preferences among herbivores: Amphipods (Ampithoe lacertosa) selectively consumed diseased eelgrass, while isopods and snails selectively grazed asymptomatic leaves, suggesting different herbivore taxa may have contrasting impacts on disease dynamics. Our experiments show no sign that herbivores directly vector Lz from diseased to asymptomatic eelgrass. However, we isolated live Lz from isopod, amphipod, and snail feces and detected Lz with quantitative polymerase chain reaction in amphipods and snails, suggesting that herbivores eating diseased eelgrass could pass the live pathogen. Finally, field surveys demonstrated a close association between seagrass wasting disease and invertebrate grazing scars; disease prevalence was 29 ± 4.7% (95% CI) higher on eelgrass leaves with herbivore scars. Collectively, these findings show that some herbivores can increase eelgrass disease risk by facilitating the spread of an important pathogen via wounding, but not via direct transmission. Thus, herbivores may play different roles in plant disease dynamics in terrestrial versus marine ecosystems depending on the pathogen's ability to survive and transmit without a vector. 

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2. Manipulation of the seagrass‐associated microbiome reduces disease severity

   https://doi.org/10.1111/1462-2920.16582  

   Graham, Olivia J; Adamczyk, Emily M; Schenk, Siobhan; Dawkins, Phoebe; Burke, Samantha; Chei, Emily; Cisz, Kaitlyn; Dayal, Sukanya; Elstner, Jack; Hausner, Arjun_Lev Pillai; et al (February 2024, Environmental Microbiology)

   Abstract Host‐associated microbes influence host health and function and can be a first line of defence against infections. While research increasingly shows that terrestrial plant microbiomes contribute to bacterial, fungal, and oomycete disease resistance, no comparable experimental work has investigated marine plant microbiomes or more diverse disease agents. We test the hypothesis that the eelgrass (Zostera marina) leaf microbiome increases resistance to seagrass wasting disease. From field eelgrass with paired diseased and asymptomatic tissue,16S rRNAgene amplicon sequencing revealed that bacterial composition and richness varied markedly between diseased and asymptomatic tissue in one of the two years. This suggests that the influence of disease on eelgrass microbial communities may vary with environmental conditions. We next experimentally reduced the eelgrass microbiome with antibiotics and bleach, then inoculated plants withLabyrinthula zosterae, the causative agent of wasting disease. We detected significantly higher disease severity in eelgrass with a native microbiome than an experimentally reduced microbiome. Our results over multiple experiments do not support a protective role of the eelgrass microbiome againstL. zosterae. Further studies of these marine host–microbe–pathogen relationships may continue to show new relationships between plant microbiomes and diseases. 

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3. Microbiota assembly in Zostera marina during early host development across controlled growth experiments

   https://doi.org/10.1128/msystems.00722-26  

   Chaput, Gina; Deen, Emma A; Pham, Eric Q; Crystal, Sarah; Matayoshi, Andrew; Andeer, Peter; Northen, Trent R; Eisen, Jonathan A; Stachowicz, John J; Sogin, E Maggie (July 2026, mSystems)

   Bittleston, Leonora S (Ed.)

   ABSTRACT Seagrass restoration practices are evolving to leverage microbiome applications, similar to agricultural systems that have demonstrated how targeted microbial communities enhance crop resilience in challenging environments. While adult seagrass microbiome research has expanded significantly, research on the seed microbiome remains critically understudied. This gap is important given that seeds represent a large portion of restoration efforts. Advancing seed microbiome research requires standardized experimental systems for controlled plant–microbe interaction studies, which are currently lacking in seagrass research. Here, we tested fabricated ecosystem devices (EcoFAB 2.0) as a standardized system for growingZostera marina(eelgrass) seedlings, enabling a controlled study of aquatic plant–microbe interactions. Using these chambers, we addressed three key questions: (i) can we reliably grow eelgrass in a controlled laboratory setting, (ii) can we manipulate eelgrass microbiota assembly and its long-term trajectory, and (iii) can we detect shifts in the microbiota during plant development (host filtering)? Host morphology measurements and 16S rRNA gene amplicon sequencing were used to track microbiota assembly across three early developmental stages of the host. Because plants were grown in a sterile environment, surface sterilization of seeds (bleach and ethanol) removed epiphytes without disturbing the shared endophytic community, yet microbiota composition remained divergent at Stage 6 (143 differentially abundant ASVs), indicating that seed coat epiphytes make a lasting and distinct contribution to assembly trajectory. We also identified 26 stage-specific indicator ASVs across eelgrass development, suggesting stage-specific microbial associations during seedling establishment. This work demonstrates the potential for targeted manipulation of the microbiome in seagrass for restoration efforts.IMPORTANCEUsing the Fabricated Ecosystem 2.0 (EcoFAB 2.0), we were able to successfully control the microbial environment of eelgrass,Zostera marina, resulting in the reduction of epiphytes and maintaining low microbial diversity across plants without compromising the morphology and growth of seedlings. Our findings advance the marine plant model system,Z. marina, by identifying taxonomic indicators across life stages. This work lays the foundation for a targeted understanding and application of microbiomes for seagrass restoration, bridging the critical knowledge gap between agricultural seed microbiome success and marine restoration applications. 

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4. Microbiome depletion and recovery in the sea anemone, Exaiptasia diaphana , following antibiotic exposure

   https://doi.org/10.1128/msystems.01342-23  

   MacVittie, Sophie; Doroodian, Saam; Alberto, Aaron; Sogin, Maggie (May 2024, mSystems)

   Wilkins, Laetitia_G E (Ed.)

   ABSTRACT Microbial species that comprise host-associated microbiomes play an essential role in maintaining and mediating the health of plants and animals. While defining the role of individual or even complex communities is important toward quantifying the effect of the microbiome on host health, it is often challenging to develop causal studies that link microbial populations to changes in host fitness. Here, we investigated the impacts of reduced microbial load following antibiotic exposure on the fitness of the anemone,Exaiptasia diaphanaand subsequent recovery of the host’s microbiome. Anemones were exposed to two different types of antibiotic solutions for 3 weeks and subsequently held in sterilized seawater for a 3-week recovery period. Our results revealed that both antibiotic treatments reduced the overall microbial load during and up to 1 week post-treatment. The observed reduction in microbial load was coupled with reduced anemone biomass, halted asexual reproduction rates, and for one of the antibiotic treatments, the partial removal of the anemone’s algal symbiont. Finally, our amplicon sequencing results of the 16S rRNA gene revealed that anemone bacterial composition only shifted in treated individuals during the recovery phase of the experiment, where we also observed a significant reduction in the overall diversity of the microbial community. Our work implies that theE. diaphana’smicrobiome contributes to host fitness and that the recovery of the host’s microbiome following disturbance with antibiotics leads to a reduced, but stable microbial state.IMPORTANCEExaiptasia diaphanais an emerging model used to define the cellular and molecular mechanisms of coral-algal symbioses.E. diaphanaalso houses a diverse microbiome, consisting of hundreds of microbial partners with undefined function. Here, we applied antibiotics to quantify the impact of microbiome removal on host fitness as well as define trajectories in microbiome recovery following disturbance. We showed that reduction of the microbiome leads to negative impacts on host fitness, and that the microbiome does not recover to its original composition while held under aseptic conditions. Rather the microbiome becomes less diverse, but more consistent across individuals. Our work is important because it suggests that anemone microbiomes play a role in maintaining host fitness, that they are susceptible to disturbance events, and that it is possible to generate gnotobiotic individuals that can be leveraged in microbiome manipulation studies to investigate the role of individual species on host health. 

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5. Weighing the risks and benefits of flowering early in the spring for the woody perennial Prunus pumila

   https://doi.org/10.1002/ajb2.16417  

   Lake_Diver, Danielle A; Savage, Jessica A (November 2024, American Journal of Botany)

   Abstract PremiseThere are advantages to flowering early in the spring, including greater pollinator fidelity and longer fruit maturation time. But plant phenology has advanced in recent years, making many plants vulnerable to freezing damage from late frosts. MethodsTo determine the costs and benefits of flowering early in the growing season, we exposedPrunus pumilaplants to two freezing treatments and a delayed flowering treatment in subsequent years. Data were collected on ovary swelling, fruit production, and pollinator visitation on hand‐ and open‐pollinated plants in all treatments. We also measured tissue damage after freeze events. ResultsOur results suggest that flowering time and temperature affect reproductive success, with fewer fruits produced after hard freezes. The same was not true for light freezes, which had minimal impact on reproduction. Freezing damage to plants after a hard freeze did affect the number of dipteran pollinators but not the overall pollinator visitation rate. Despite the clear impact of freezing temperatures on plant reproduction, flowering early provided an advantage in that reproductive output decreased with delayed flowering. ConclusionsOur findings suggest thatPrunus pumilawill retain the ability to attract pollinators and produce viable seeds if exposed to false spring conditions that involve a light freeze, but hard freezes may reduce yield by an order of magnitude. Although the advantages to flowering early may outweigh the risk of freezing damage under current conditions, it is possible that flower viability may be constrained under continued climate warming. 

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