Abstract
Sponges (phylum Porifera) are important members of almost all aquatic ecosystems, and are renowned for hosting often dense and diverse microbial communities. While the specificity of the sponge microbiota seems to be closely related to host phylogeny, the environmental factors that could shape differences within local sponge-specific communities remain less understood. On tropical coral reefs, sponge habitats can span from shallow areas to deeper, mesophotic sites. These habitats differ in terms of environmental factors such as light, temperature, and food availability, as well as anthropogenic impact. In order to study the host specificity and potential influence of varying habitats on the sponge microbiota within a local area, four tropical reef sponges, Rhabdastrella globostellata, Callyspongia sp., Rhaphoxya sp., and Acanthella cavernosa, were collected from exposed shallow reef slopes and a deep reef drop-off. Based on 16S rRNA gene pyrosequencing profiles, beta diversity analyses revealed that each sponge species possessed a specific microbiota that was significantly different to those of the other species and exhibited attributes that are characteristic of high- and/or low-microbial-abundance sponges. These findings emphasize the influence of host identity on the associated microbiota. Dominant sponge- and seawater-associated bacterial phyla were Chloroflexi, Cyanobacteria, and Proteobacteria. Comparison of individual sponge taxa and seawater samples between shallow and deep reef sites revealed no significant variation in alpha diversity estimates, while differences in microbial beta diversity (variation in community composition) were significant for Callyspongia sp. sponges and seawater samples. Overall, the sponge-associated microbiota is significantly shaped by host identity across all samples, while the effect of habitat differentiation seems to be less predominant in tropical reef sponges.
Highlights
In marine ecosystems, sponges represent common and versatile members of the benthos, with distribution ranges along large environmental gradients and across various habitats including deep sea benthos, seamounts, polar regions, and temperate and tropical coral reefs (Bell, 2008)
We apply high-throughput 16S rRNA gene amplicon pyrosequencing to profile four demosponge species, Rhabdastrella globostellata, Callyspongia sp., Acanthella cavernosa, and Rhaphoxya sp., collected with surrounding seawater to address the following aims: (1) based on all available samples we investigate the degree of host specificity of microbial communities among several tropical sponge species, and (2) based on a habitat-specific subset of samples we estimate the influence of local habitat variation on sponge- and seawater-associated microbial community patterns
Coverage was slightly higher for A. cavernosa and R. globostellata compared to seawater and Callyspongia sp. samples (Table 2)
Summary
Sponges represent common and versatile members of the benthos, with distribution ranges along large environmental gradients and across various habitats including deep sea benthos, seamounts, polar regions, and temperate and tropical coral reefs (Bell, 2008). Many sponges are notable for their diverse and abundant microbial biota, with up to 35% of sponge biomass being made up of microbes (Taylor et al, 2007). Sponge-microbe relationships can include microbial cells as a food source for filterfeeding sponges, carbon- and nitrogen-based nutritional interactions, and the synthesis of secondary metabolites for chemical defence mechanisms (Hentschel et al, 2012; Taylor et al, 2007). Accumulated evidence indicates that much of the sponge microbiota is specific to, or at the very least heavily enriched in, sponge hosts (Lee et al, 2011; Pita et al, 2013; Schmitt, Hentschel & Taylor, 2012; Webster et al, 2010; Simister et al, 2012a). In addition to the apparent influence of host identity on microbial composition (Easson & Thacker, 2014; Naim et al, 2014; Pita et al, 2013; Reveillaud et al, 2014), marine sponge-associated microbial communities exhibit relatively high temporal and biogeographic stability (e.g., Simister et al, 2013; Hardoim & Costa, 2014; Taylor et al, 2005)
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