Bacterial Community Associated with the Reef Coral Mussismilia braziliensis's Momentum Boundary Layer over a Diel Cycle

Abstract

Corals display circadian physiological cycles, changing from autotrophy during the day to heterotrophy during the night. Such physiological transition offers distinct environments to the microbial community associated with corals: an oxygen-rich environment during daylight hours and an oxygen-depleted environment during the night. Most studies of coral reef microbes have been performed on samples taken during the day, representing a bias in the understanding of the composition and function of these communities. We hypothesized that coral circadian physiology alters the composition and function of microbial communities in reef boundary layers. Here, we analyzed microbial communities associated with the momentum boundary layer (MBL) of the Brazilian endemic reef coral Mussismilia braziliensis during a diurnal cycle, and compared them to the water column. We determined microbial abundance and nutrient concentration in samples taken within a few centimeters of the coral's surface every 6 h for 48 h, and sequenced microbial metagenomes from a subset of the samples. We found that dominant taxa and functions in the coral MBL community were stable over the time scale of our sampling, with no significant shifts between night and day samples. Interestingly, the two water column metagenomes sampled 1 m above the corals were also very similar to the MBL metagenomes. When all samples were analyzed together, nutrient concentration significantly explained 40% of the taxonomic dissimilarity among dominant genera in the community. Functional profiles were highly homogenous and not significantly predicted by any environmental variables measured. Our data indicated that water flow may overrule the effects of coral physiology in the MBL bacterial community, at the scale of centimeters, and suggested that sampling resolution at the scale of millimeters may be necessary to address diurnal variation in community composition.

Characterizing the ecology of coral reef microorganisms across different scales within the Caribbean

“…Despite the above findings, a few field-based investigations did not observe differences in the seawater microbial composition or function surrounding corals compared to seawater sampled further away from the reef substrate (e. g. Silveira et al 2017;Walsh et al 2017), demonstrating that there is still much to be learned about potential coral -microbial interactions and the significance of these interactions for pathogen/symbiont recruitment and benthic-pelagic coupling on coral reefs. For example, how do environmental differences between reef locations impact coral-microbial dynamics surrounding individual coral colonies?…”

Tropical stony corals host diverse microbial nitrogen dynamics

“…Ambient nutrient concentrations have been shown to impact the microbial communities of corals, with local variations from 5-11 imol L-in total nitrogen explaining up to 40% of the taxonomic dissimilarity among dominant genera in a community of the tropical stony coral Mussismilia braZiliensis on a single reef (Silveira et al, 2017). The rate data from the present study do display an apparent correlation with ambient DIN concentrations ( Figure 4.2), although a larger sample size and analysis of the same species across various sites would contribute to explaining this trend more rigorously.…”

The coral ecosphere: A unique coral reef habitat that fosters coral–microbial interactions

“…Despite collecting large volumes (10 liters) of seawater that may have integrated the microbial heterogeneity that exists at smaller scales, Tout et al () found enrichment of copiotrophic bacteria near the corals, as well as genes used for bacterial motility, chemotaxis, membrane transport, iron acquisition, and metabolism of aromatic compounds in addition to other pathways. In contrast, Silveira et al () did not detect any significant differences in the functional or taxonomic microbial composition between large (80 liters) volume samples of near‐coral seawater (CSW) collected surrounding patches of the coral Mussismilia braziliensis and the water column. A study by Walsh et al () detected differences in the microbial communities of seawater within 5 cm of reef macro‐organisms compared to seawater sampled 3 m off of the reef except for the coral M. braziliensis , similar to the study conducted by Silveira et al ().…”

“…In contrast, Silveira et al () did not detect any significant differences in the functional or taxonomic microbial composition between large (80 liters) volume samples of near‐coral seawater (CSW) collected surrounding patches of the coral Mussismilia braziliensis and the water column. A study by Walsh et al () detected differences in the microbial communities of seawater within 5 cm of reef macro‐organisms compared to seawater sampled 3 m off of the reef except for the coral M. braziliensis , similar to the study conducted by Silveira et al (). Finally, a recent study used syringes (50 mL volume) to sample seawater 0, 5, and 50 cm away from individual colonies of Acropora and Platygyra spp.…”

“…Previous investigations of reef water microbial community dynamics have revealed relationships among the composition of reef macrofauna, the composition and metabolism of bacteria and archaea in reef seawater (RSW), the abundances of heterotrophic bacteria and virulence genes, and coral health (Dinsdale et al ; Kelly et al ; Kelly et al ; Haas et al ). In addition, recent studies have suggested the existence of a previously unrecognized coral‐associated microbial environment: the seawater adjacent to corals (Tout et al ; Silveira et al ; Walsh et al ; Ochsenkuhn et al ).…”