Abstract
Sea urchins strongly affect reef ecology, and the bacteria associated with their gut digesta have not been well studied in coral reefs. In the current study, we analyze the bacterial composition of five sea urchin species collected from Luhuitou fringing reef, namely Stomopneustes variolaris, Diadema setosum, Echinothrix calamaris, Diadema savignyi, and Tripneustes gratilla, using high-throughput 16S rRNA gene-based pyrosequencing. Propionigenium, Prolixibacter, and Photobacterium were found to be the dominant bacterial genera in all five species. Interestingly, four sea urchin species, including S. variolaris, D. setosum, E. calamaris, and D. savignyi, displayed a higher mean total abundance of the three bacterial genera (69.72 ± 6.49%) than T. gratilla (43.37 ± 13.47%). Diversity analysis indicated that the gut digesta of sea urchin T. gratilla displayed a higher bacterial α-diversity compared with the other four species. PCoA showed that the four groups representing D. setosum, D. savignyi, E. calamaris, and S. variolaris were overlapping, but distant from the group representing T. gratilla. Predictive metagenomics performed by PICRUSt revealed that the abundances of genes involved in amino acid metabolism and metabolism of terpenoid and polyketide were higher in T. gratilla, while those involved in carbohydrate metabolism were higher in the other four sea urchin species. Therefore, our results indicated that the composition, diversity and predictive metabolic profiles of bacteria associated with the gut digesta of T. gratilla were significantly different from those of the other four sea urchin species in Luhuitou fringing reef.
Highlights
Sea urchins play a dual role in the health and stability of coral reef ecosystems (Lawrence, 2013)
A total of 40 sea urchin samples belonging to five species (Stomopneustes variolaris, Diadema setosum, Echinothrix calamaris, Diadema savignyi, and Tripneustes gratilla, Figure 2) and four genera were collected from the Luhuitou fringing reef
The analysis indicated that the gut digesta in T. gratilla consisted almost entirely of macroalgae fragments, with no evidence of corals and their calcium carbonate skeleton, while the digesta of the other four sea urchin species were dominated by coral and their calcium carbonate skeleton, turf algae, filamentous algae, silt and calcareous algae
Summary
Sea urchins play a dual role in the health and stability of coral reef ecosystems (Lawrence, 2013). Some sea urchin species, such as Tripneustes gratilla (Herring, 1972; Carreiro-Silva and McClanahan, 2001) and Mierocyphus rousseau (Herring, 1972; Rotjan and Lewis, 2008), play a positive role in coral growth and recruitment by feeding on algae, controlling their overgrowth. Some sea urchin species, such as Diadema setosum (Carreiro-Silva and McClanahan, 2001; Qiu et al, 2014), Echinometra mathaei (Bronstein and Loya, 2014), and Eucidaris thouarsii (Herring, 1972; Glynn et al, 1979), negatively affect coral reefs by feeding on coral tissue and skeletons. Most studies in this field far have mainly focused on the macroscopic ecology (e.g., feeding ecology and influence on coral and algae), with little research on the post-ingestive processes (e.g., food digestion and related processes) that are related to host macroscopic ecology
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