The recent ASLO Aquatic Sciences Meeting held in Palma de Mallorca, Spain, was an exciting platform for researchers to delve into the fascinating realm of host-microbiome interactions and their role in protecting and restoring marine ecosystems. As the session chair, I witnessed groundbreaking presentations that shed light on the hidden world of microbes and their impact on diverse marine organisms.

One captivating study conducted by Xesca Reynés from IMEDEA (Spain) focused on the influence of microbiomes on the germination and development of seagrass. Through laboratory experiments using Cymodocea nodosa seeds, Reynés demonstrated the significant role of specific microorganisms in the success of germination and growth. These findings underline the importance of considering the seed microbiome and sediment type in seagrass conservation and restoration efforts.

Another noteworthy presentation by Katharina Kesy from the University of Greifswald (Germany) explored the response of Zostera marina microbiomes to seagrass restoration in the German Baltic Sea. By analyzing the shifts in microbiomes of transplanted seagrass shoots over several months, Kesy uncovered intriguing patterns. While seagrass establishment was successful at restored sites, there was an initial disturbance in the leaf microbiome. However, after three months, the leaf microbiomes resembled those of the nearby donor meadow, indicating location-specific effects. Interestingly, the root microbiomes exhibited greater variability across plants, time, and space, highlighting the heterogeneity of this habitat. These findings emphasize the importance of considering microbial functional traits rather than specific microbes in restoration site selection.

Maren Ziegler from Justus Liebig University Giessen (Germany) tackled the complex relationship between environmental conditions, holobiont composition, and phenotype using innovative holobiont engineering approaches. By priming the environment and transplanting microbiomes, Ziegler revealed the potential to induce stress-tolerant phenotypes in corals. The selective engineering of host-symbiont compositions through a coral model system enabled a deeper understanding of microbiome functions within the holobiont. These findings contribute to active intervention and assisted evolution, providing insights into leveraging microbiota to aid coral holobiont adaptation and combat the ongoing coral crisis.

Tyler Griffin from the University of Connecticut (USA) provided valuable insights into the gut microbiome of the blue mussel Mytilus edulis. Analyzing data from seven studies, Griffin identified a clear distinction between microbial communities in mussels that underwent a no-food period and those that did not. This discovery aligns with the emerging understanding of transient versus resident microbes within the digestive tissues. Griffin’s study underscores the importance of conducting multi-study analyses of raw microbiome sequence data and tailoring experimental designs to address specific research questions.

In a remarkable pilot study, Lauren Speare from Oregon State University (USA) explored the potential of predatory bacteria in treating vibrio-induced bleaching in staghorn corals. By exposing corals to pathogens followed by inoculation with the predatory bacterium Halobacteriovorax, Speare aimed to understand the impact of bacterial predators on animal microbiomes and community structure. These findings have profound implications for comprehending the top-down controls within microbial ecosystems and their role in coral restoration efforts.

Lastly, Rebecca Vega Thurber, also from Oregon State University (USA), shed light on the factors driving the global declines in coral abundance and diversity, focusing on infectious microbial diseases in Caribbean coral reefs. Acropora cervicornis, a critically endangered coral species, faces heightened vulnerability to disease, particularly due to the bacterial parasite ‘Ca. Aquarickettsia rohweri.’ Thurber’s study investigated how nutrient enrichment affects the parasite’s physiology within its host. Through microscopy and transcriptomic analyses, the study revealed the parasite’s transition from intracellular sites to mucocytes for release into the environment. The upregulation of genes associated with energy scavenging, signalling, virulence, two-component systems, and nutrient import suggests the parasite’s response to elevated nutrient levels. These findings provide crucial insights into the mechanisms behind induced disease susceptibility in A. cervicornis and implicate nutrient exposure in the horizontal transmission of the parasite.

The presentations at the ASLO Aquatic Sciences Meeting truly expanded our understanding of the intricate relationships between hosts and their microbial partners in marine ecosystems. By unravelling the roles of microbiomes in seed germination, seagrass restoration, coral adaptation, gut health, and disease prevention, these researchers are paving the way for innovative strategies in marine community protection and restoration. With each revelation, we come closer to unlocking the immense potential of microbial interactions for safeguarding our precious marine environments.