Archaeal communities of low and high microbial abundance sponges inhabiting the remote western Indian Ocean island of Mayotte.

Marine sponges are abundant and ecologically important components of coral reefs and have been shown to harbour exceptionally high microbial densities, which can differ substantially among sponge species. However, this dichotomy between high and low microbial abundance (HMA, LMA) sponges is still not fully understood, particularly as concerns the archaeal community. This study aims to fill this gap by analysing (using 454-pyrosequencing of the 16S rRNA gene) how the archaeal community varies among known LMA (Stylissa carteri, and Stylissa massa), known HMA (Hyrtios erectus and Xestospongia testudinaria) and unknown HMA/LMA status sponge species (Ectyoplasia coccinea, Paratetilla bacca and Petrosia aff. spheroida) collected in a remote location in which very few sponge microbial composition studies have been previously performed (Mayotte, Comores archipelago, France) and comparing the results with those reported in four other geographical areas. Based on archaeal community composition, the known LMA sponges formed a distinct cluster together with Paratetilla bacca, Ectyoplasia coccinea and seawater while the known HMA sponge X. testudinaria formed a cluster with Petrosia aff. spheroida. The known HMA sponge H. erectus, in turn, had an intermediate archaeal community between HMA sponges and sediment samples. In addition to the above, we also showed significant compositional congruence between archaeal and bacterial communities sampled from the same sponge individuals. HMA sponges were mainly dominated by members assigned to the genus Nitrosopumilus while LMA sponges were mainly dominated by members assigned to the genus Cenarchaeum. In general, there was no clear difference in richness between HMA and LMA sponges. Evenness, however, was higher in HMA than LMA sponges. Whilst the present study corroborates some of the traits commonly associated with the HMA-LMA dichotomy (higher evenness in Mayotte HMA sponges), this was not consistent across geographical areas showing that more research is needed to fully understand the HMA/LMA dichotomy as concerns Archaea.

Comparison of archaeal and bacterial communities in two sponge species and seawater from an Indonesian coral reef environment.

Most existing coral reef studies have focused on a single biotope and a single domain (Archaea or Bacteria). Few coral reef studies have explored the archaeal and bacterial community simultaneously. In this study, we compare the diversity and composition of archaeal and bacterial communities in seawater and two closely related sponge species (Stylissa carteri and Stylissa massa) in the Berau reef system, Indonesia. A 16S rRNA gene barcoded pyrosequencing approach was used to test to what extent seawater, S. carteri and S. massa host compositionally distinct communities of Archaea and Bacteria. Proteobacteria dominated the bacterial communities of all three studied biotopes whereas Euryarchaeota was the most abundant archaeal phylum in seawater and Crenarchaeota the most abundant archaeal phylum in both Stylissa species. Biotopes explained 56% and 53% of the variation in archaeal and bacterial composition respectively and there was significant congruence between the composition of archaeal and bacterial communities. These results suggest that the processes that drive bacterial composition within the studied biotopes may be fundamentally similar to those that drive archaeal composition.

Habitat and water quality variables as predictors of community composition in an Indonesian coral reef: a multi-taxon study in the Spermonde Archipelago.

Assemblages of corals, sponges, foraminifera, sediment bacteria and sediment archaea were assessed at two depths in the Spermonde Archipelago. Our goal was to assess to what extent variation in composition could be explained by habitat and water quality variables. The habitat variables consisted of depth, substrate type and scleractinian coral cover while water quality variables were derived from ocean color satellite imagery, including the colored dissolved organic matter index (CDOM), chlorophyll-a (Chlor-a) and remote sensing reflectance at 645n m (Rrs_645). Together, habitat and water quality variables explained from 31% (sediment bacteria) to 80% (forams) of the variation in composition. The variation in composition of corals, sponges, forams and sediment archaea was primarily related to habitat variables, while the variation in composition of sediment bacteria was primarily related to water quality variables. Habitat and water quality variables explained similar amounts of variation in the composition of corals and sediment bacteria. CDOM (sponges, sediment bacteria and sediment archaea), Chlor-a (corals and forams) and Rrs_645 (sponges and forams) proved significant predictors of variation in composition for the studied taxa. In addition to water quality variables, all taxa responded to a range of habitat variables including depth and the percentage cover of various benthic life forms including coral cover variables, rubble and sand. Sand cover was the most important habitat variable for corals, sponges, sediment bacteria and sediment archaea. Coral life forms including the cover of branching and tabular corals were important habitat variables for sponges and forams. These results show marked differences in how various taxa respond to variation in habitat and water quality in the Spermonde Archipelago. Moreover, our results indicate that variables estimated from ocean color satellite imagery proved to be better predictors of variation in marine community composition than commonly-used proxies such as the distance offshore or distance to the nearest river.