Population structure of the hydrocoral Millepora platyphylla in habitats experiencing different flow regimes in Moorea, French Polynesia.

While the fire coral Millepora platyphylla is an important component of Indo-Pacific reefs, where it thrives in a wide range of environments, the ecological and biological processes driving its distribution and population structure are not well understood. Here, we quantified this species' population structure in five habitats with contrasting hydrodynamic regimes in Moorea, French Polynesia; two in the fore reef: mid and upper slopes, and three in the lagoon: back, fringing and patch reefs. A total of 3651 colonies of fire corals were mapped and measured over 45,000 m2 of surveyed reef. Due to the species' sensitivity to fragmentation in response to strong water movement, hydrodynamic conditions (e.g. waves, pass and lagoonal circulation) corresponded to marked differences in colony size distributions, morphology and recruitment dynamics among habitats. The size structure varied among reef habitats with higher proportions of larger colonies in calm nearshore reefs (fringing and patch reefs), while populations were dominated by smaller colonies in the exposed fore reefs. The highest densities of fire corals were recorded in fore reef habitats (0.12-0.20 n.m-2) where the proportion of recruits and juveniles was higher at mid slope populations (49.3%) than on the upper slope near where waves break (29.0%). In the latter habitat, most colonies grew as vertical sheets on encrusting bases making them more vulnerable to colony fragmentation, whereas fire corals were encrusting or massive in all other habitats. The lowest densities of M. platyphylla occurred in lagoonal habitats (0.02-0.04 n.m-2) characterized by a combination of low water movement and other physical and biological stressors. This study reports the first evidence of population structure of fire corals in two common reef environments and illustrates the importance of water flow in driving population dynamic processes of these reef-building species

Naturally occurring fire coral clones demonstrate a genetic and environmental basis of microbiome composition

International audienceCoral microbiomes are critical to holobiont functioning, but much remains to be understood about how prevailing environment and host genotype affect microbial communities in ecosystems. Resembling human identical twin studies, we examined bacterial community differences of naturally occurring fire coral clones within and between contrasting reef habitats to assess the relative contribution of host genotype and environment to microbiome structure. Bacterial community composition of coral clones differed between reef habitats, highlighting the contribution of the environment. Similarly, but to a lesser extent, microbiomes varied across different genotypes in identical habitats, denoting the influence of host genotype. Predictions of genomic function based on taxonomic profiles suggest that environmentally determined taxa supported a functional restructuring of the microbial metabolic network. In contrast, bacteria determined by host genotype seemed to be functionally redundant. Our study suggests microbiome flexibility as a mechanism of environmental adaptation with association of different bacterial taxa partially dependent on host genotype

Morphology of <i>Millepora platyphylla</i> adult colonies across the five surveyed habitats.

<p>Proportions of colonies with encrusting, sheet tree and massive morphology were averaged by habitats and error bars show the standard error for transect replicates. Similar letters over each set of bars indicate no statistical difference in post-hoc comparisons for a given morphology among habitats (<i>P ></i> 0.05). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173513#pone.0173513.g002" target="_blank">Fig 2</a> for photos of each of the morphologies.</p

Index describing the population size structure and recruitment for <i>Millepora platyphylla</i> across the five habitats surveyed.

<p>Index describing the population size structure and recruitment for <i>Millepora platyphylla</i> across the five habitats surveyed.</p

Morphologies of <i>Millepora platyphylla</i> colonies in habitats experiencing contrasting hydrodynamic regimes.

<p>(A) Encrusting wave-tolerant morphology in the mid slope, a fore reef habitat at 13 m; (B) sheet tree morphology vulnerable to wave-induced breakage in the upper slope, a fore reef habitat at 6 m and (C) massive wave-tolerant morphology in the patch reef, a lagoonal habitat (photo is courtesy of Gilles Siu).</p

Non-metric multidimensional scaling (MDS) plot of <i>Millepora platyphylla</i> population structure across the five surveyed habitats.

<p>Different shapes indicate the three transects for each habitat and grey lines show clusters given by dendogram based on Eucledian distance of 4 at a stress level of 0.09. The surimposed red lines define the Eucledian distance coefficient on normalized data based on Spearman ranking, with each vector having lengths ≥ 0.4: density, cover, distribution index, mean neighborhood distance, mean height and size of adults, and proportion of recruits (< 1 cm²), juveniles (1–20 cm²) and adults (> 20 cm²). The second transect of the fringing reef is shown as a single group mostly related to a small population size (i.e. 27 colonies, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173513#pone.0173513.s002" target="_blank">S2 Table</a>).</p

Aerial views of the locations of each transect in the five surveyed habitats in Moorea, French Polynesia.

<p>The names of these surveyed locations are: (A) Tiahura, (B) Papetoai, (C) Cook’s Bay and (D) Temae. Map data WorldView–2, Digital Globe.</p

Stock-recruitment relationship between the abundance of adults and coral new recruits and juveniles.

<p>(A) Significant positive relationship in the lagoon (i.e. back, fringing and patch reefs) and (B) no stock-recruitment relationship in the fore reef (i.e. mid and upper slopes). Each dot represents the mean abundance for each transect surveyed. Note the different scales on x and y axes.</p