Abstract
Marine sponges host dense, diverse, and species-specific microbial communities around the globe; however, most of the current knowledge is restricted to species from tropical and temperate waters. Only recently, some studies have assessed the microbiome of a few Antarctic sponges; however, contrary to low mid-latitude sponges, the knowledge about temporal (stability) patterns in the bacterial communities of Antarctic sponges is absent. Here, we studied the temporal patterns of bacterial communities in the Antarctic sponges Mycale (Oxymycale) acerata, Isodictya sp., Hymeniacidon torquata, and Tedania (Tedaniopsis) wellsae that were tagged in situ and monitored during three austral summers over a 24-month period. By using amplicon sequencing of the bacterial 16S rRNA gene we found that the microbiome differed between species. In general, bacterial communities were dominated by gammaproteobacterial OTUs; however, M. acerata showed the most distinct pattern, being dominated by a single betaproteobacterial OTU. The analysis at OTU level (defined at 97% sequence similarity) showed a highly stable bacterial community through time, despite the abnormal seawater temperatures (reaching 3°C) and rates of temperature increase of 0.15°C day–1 recorded in austral summer 2017. Sponges were characterized by a small core bacterial community that accounted for a high percentage of the abundance. Overall, no consistent changes in core OTU abundance were recorded for all studied species, confirming a high temporal stability of the microbiome. In addition, predicted functional pathway profiles showed that the most abundant pathways among all sponges belonged mostly to metabolism pathway groups (e.g., amino acid, carbohydrate, energy, and nucleotide). The predicted functional pathway patterns differed among the four sponge species. However, no clear temporal differences were detected supporting what was found in terms of the relatively stable composition of the bacterial communities.
Highlights
Marine sponges (Phylum Porifera) are considered reservoirs of exceptional microbial diversity, constituting a major contributor to the total prokaryotic diversity of the world’s oceans (Thomas et al, 2016)
Our results showed that studied sponges host different bacterial communities, being dominated by Proteobacteria and Bacteroidetes which is in accordance with previous studies on other Antarctic sponges that has classified them as low microbial abundance (LMA) species (Rodríguez-Marconi et al, 2015; Cárdenas et al, 2018a; Steinert et al, 2019)
Barnes (2017) provided insights of the dramatic effects of ice scour in shallow areas around the Western Antarctic Peninsula (WAP), where in some areas such as Ryder Bay (Adelaide Island), about 25% of the substrate is hit by icebergs each year. This type of estimation was not carried out in our study area, the impact of ice scour was often observed, even increasing in late summer (February) 2016, affecting our study site by removing sponges and moorings containing temperature dataloggers. This shows the difficulties of working in such an extreme environment, yet highlights the importance of the results presented here, as they provide the first insights on the temporal patterns of bacterial communities associated with Antarctic sponges
Summary
Marine sponges (Phylum Porifera) are considered reservoirs of exceptional microbial diversity, constituting a major contributor to the total prokaryotic diversity of the world’s oceans (Thomas et al, 2016). According to the abundance of bacterial symbionts, sponges have been classified as high microbial abundance (HMA) and low microbial abundance (LMA) (Vacelet and Donadey, 1977; Hentschel et al, 2003; Gloeckner et al, 2014). This classification incorporates distinctions in terms of abundance, and diversity, specificity, as well as host physiology and morphology (Hentschel et al, 2003; Weisz et al, 2008; Schläppy et al, 2010; Moitinho-Silva et al, 2017). While some sponge-associated microbiomes tend to be highly stable when exposed to stress (Simister R. et al, 2012; Luter et al, 2014; Pineda et al, 2016), other studies have reported shifts and even disruption of the microbiome (see Lemoine et al, 2007; Webster et al, 2008; Fan et al, 2013; Ramsby et al, 2018)
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