Seagrasses can form mutualisms with their microbiomes that facilitate the exchange of energy sources, nutrients, and hormones, and ultimately impact plant stress resistance. Little is known about community succession within the belowground seagrass microbiome after disturbance and its potential role in the plant’s recovery after transplantation. We transplanted Zostera marina shoots with and without an intact rhizosphere, and cultivated plants for four weeks while characterizing microbiome recovery and effects on plant traits. Rhizosphere and root microbiomes were compositionally distinct, likely representing discrete microbial niches. Furthermore, microbiomes of washed transplants were initially different from those of sod transplants, and recovered to resemble an undisturbed state within fourteen days. Conspicuously, changes in microbial communities of washed transplants corresponded with changes in rhizosphere sediment mass and root biomass, highlighting the strength and responsive nature of the relationship between plants, their microbiome, and the environment. Potential mutualistic microbes that were enriched over time include those that function in the cycling and turnover of sulfur, nitrogen, and plant-derived carbon in the rhizosphere environment. These findings highlight the importance and resiliency of the seagrass microbiome after disturbance. Consideration of the microbiome will have meaningful implications on habitat restoration practices. Importance Seagrasses are important coastal species that are declining globally, and transplantation can be used to combat these declines. However, the bacterial communities associated with seagrass rhizospheres and roots (the microbiome) are often disturbed or removed completely prior to transplantation. The seagrass microbiome benefits seagrasses through metabolite, nutrient, and phytohormone exchange, and contributes to the ecosystem services of seagrass meadows by cycling sulfur, nitrogen, and carbon. This experiment aimed to characterize the importance and resilience of the seagrass belowground microbiome by transplanting Zostera marina with and without intact rhizospheres and tracking microbiome and plant morphological recovery over four weeks. We found the seagrass microbiome to be resilient to transplantation disturbance, recovering after fourteen days. Additionally, microbiome recovery was linked with seagrass morphology, coinciding with increases in rhizosphere sediment mass and root biomass. Results of this study can be used to include microbiome responses in informing future restoration work.

18Seagrasses can form mutualisms with their microbiomes that facilitate the exchange of 19 energy sources, nutrients, and hormones, and ultimately impact plant stress resistance. Little is 20 known about community succession within the belowground seagrass microbiome after 21 disturbance and its potential role in the plant's recovery after transplantation. We transplanted 22 Zostera marina shoots with and without an intact rhizosphere and cultivated plants for four 23 weeks while characterizing microbiome recovery and effects on plant traits. Rhizosphere and 24 root microbiomes were compositionally distinct, likely representing discrete microbial niches. 25 Furthermore, microbiomes of washed transplants were initially different from those of sod 26 transplants, and recovered to resemble an undisturbed state within fourteen days. Conspicuously, 27 changes in microbial communities of washed transplants corresponded with changes in 28 rhizosphere sediment mass and root biomass, highlighting the strength and responsive nature of 29 the relationship between plants, their microbiome, and the environment. Potential mutualistic 30 microbes that were enriched over time include those that function in the cycling and turnover of 31 sulfur, nitrogen, and plant-derived carbon in the rhizosphere environment. These findings 32 highlight the importance and resiliency of the seagrass microbiome after disturbance. 33 Consideration of the microbiome will have meaningful implications on habitat restoration 34 practices. 35Importance 37 Seagrasses are important coastal species that are declining globally, and transplantation 38 can be used to combat these declines. However, the bacterial communities associated with 39 seagrass rhizospheres and roots (the microbiome) are often disturbed or removed completely 40 prior to transplantation. The seagrass microbiome benefits seagrasses through metabolite, 41 nutrient, and phytohormone exchange, and contributes to the ecosystem services of seagrass 42 meadows by cycling sulfur, nitrogen, and carbon. This experiment aimed to characterize the 43 importance and resilience of the seagrass belowground microbiome by transplanting Zostera 44 marina with and without intact rhizospheres and tracking microbiome and plant morphological 45 recovery over four weeks. We found the seagrass microbiome to be resilient to transplantation 46 disturbance, recovering after fourteen days. Additionally, microbiome recovery was linked with 47 seagrass morphology, coinciding with increases in rhizosphere sediment mass and root biomass. 48Results of this study can be used to include microbiome responses in informing future restoration 49 work. 52The rhizobiome has long been recognized to have important impacts on plant growth and 53 health (1). The microbes of the rhizobiome, which directly interact with and are influenced by 54 the roots (2), can benefit their plant hosts through recycling and producing bioavailable nutrients 55 (3-5), increasing disease resistance through competition with or in...

A growing body of research has established that the microbiome can mediate the dynamics and functional capacities of diverse biological systems. Yet, we understand little about what governs the response of these microbial communities to host or environmental changes.

Oyster aquaculture is a growing industry that depends on production of fast-growing, healthy larvae and juveniles (spat) to be sold to farmers. Despite nearly identical genetics and environmental conditions in the early life stages of oysters, larvae and spat sizes can vary drastically. As the microbiome can influence the health and size of marine invertebrates, we analyzed the microbiomes of differently-sized juvenile Pacific oyster (Crassostrea gigas) spat of the same age to examine the relationship of their microbiomes with size variation. We used 16S sequencing of 128 animals (n = 60 large, n = 68 small) to characterize the microbiomes of each size class, comparing alpha diversity, beta diversity, and differentially abundant taxa between size classes. We observed that small spat had higher alpha diversity using measures that considered only richness, but there was no difference in alpha diversity between the two size classes using measures that incorporate compositional metrics. Additionally, large and small spat had distinct microbiomes, the separation of which was driven by more dominant bacterial taxa. Taxa that were differentially abundant in large oysters were also more abundant overall, and many appear to have roles in nutrient absorption and energy acquisition. The results of this study provide insight into how the microbiome of C. gigas may affect the early development of the animal, which can inform hatchery and nursery practices.