ABSTRACT: Corals harbor a complex suite of beneficial microbial symbionts. Shuffling the composition of these symbionts could, in theory, help the host withstand rapidly emerging or geographically varying stressors without requiring genetic change to the coral itself. The relative impact of host qualities on microbiome (bacteria) composition should provide insight into the extent that shifting microbial symbionts can play in resilience to environmental disturbance on reefs. We sought to assess the differences in microbiome composition across a large spatial scale (between Puerto Rico and Bonaire; >700 km apart) and in response to localized anthropogenic impacts in 2 co-occurring Caribbean soft corals (Eunicea flexuosa and Gorgonia ventalina) with well-documented differing degrees of population genetic differentiation. Host species was the strongest determinant of microbiome composition, with between-hosts distinction due largely to differences in the abundant genera Endozoicomonas and Mycoplasma. Interestingly, the microbiome of the more genetically subdivided G. ventalina showed stronger differentiation between islands and in response to local anthropogenic impacts than the less subdivided E. flexuosa. For both hosts, anthropogenic impacts on microbiome composition were stronger in Bonaire. Again, Endozoicomonas was responsible for much of the differentiation between and within islands and included host- and island-specific sequence variants. The level of intra-species microbiome variation mirrored the known geographic differentiation of their hosts, a trend that is consistent in the literature for 8 other coral species. Thus, while potentially adaptive bacteria may shuffle in response to environmental changes, our findings suggest that most changes to microbiomes are likely constrained by host genetics.

Pores in the Seroe Domi Formation on Curacao contain large quantities of clay minerals, organic material, and protodolomite or very high-magnesium calcite (VHMC) crystals. Transmission electron microscopy (TEM) applied to bio-sectioned rock samples showed the in situ relationship between the organic material, clay minerals, and VHMC. Dumbbells, consisting of two globular bodies connected by a narrow waist, ~20 mm in length and 5–8 mm wide, characterize the organic masses. The dumbbells are coated by clay minerals. VHMC crystals grew from nucleation points within microbial films and sheaths that surround the dumbbells. DNA extraction for 16 s rRNA gene analysis revealed the presence of sulfate- and sulfur-reducing bacteria, a variety of marine cyanophytes, bacteridetes, and proteobacteria, plus freshwater cyanophytes within the rock samples. This study provides evidence from a new field locality for the microbial nucleation and growth of VHMC associated with clay minerals, and the in situ appearance of microbial dumbbells associated with dolomite. Additionally, this study is the first to reveal the internal structure of these dumbbell features indicating that they are organic in origin with crystalline material in the surrounding sheath.

Abstract
Despite their critical importance and the numerous efforts to protect, conserve and restore mangrove forests, these ecosystems are still disappearing at worrying rates around the world. Alongside these losses, many restoration projects fail to achieve their target. This is often a consequence of ignoring why the natural recovery has not occurred in the first place. In this regard, hydrogen sulfide (H2S) and its typical rotten egg smell are omnipresent components in mangrove sediments. Nevertheless, too little attention has been given to its influence on the mangrove seedlings when transplanted to an area with a different sulfide concentration compared to their original habitat. Thus, this study aims to determine the sulfide tolerance of the red mangrove (Rhizophora mangle) and black mangrove (Avicennia germinans) using experimental nurseries in areas with high and low sulfides. The results reveal that high sulfide levels (> 20 mM) have serious effects on the growth of R. mangle, while having no significant effect on A. germinans, unveiling its ability to tolerate higher concentrations. Replanting A. germinans seedlings can facilitate success when restoring degraded and highly sulfidic areas. Additionally, this study provides a novel analysis of how microbial communities of the rhizosphere of A. germinans affect the survivability of mangrove seedlings in restoration projects.