OTUs related to organic enrichment status
ANOVA revealed six OTUs with significant differences in relative abundances among organic enrichment statuses (Table 2). Of these, one OTU showed highest relative abundance in oxic A sediments and one showed highest relative abundance in oxic B sediments, and both of these two OTUs were taxonomically assigned to a nematode species Sabatieria punctata . The other four OTUs showed higher relative abundances in hypoxic and/or anoxic sediments.
Pearson’s phi coefficient analyses revealed 35 OTUs correlated significantly with organic enrichment status, with 26, eight, zero, and one OTUs for oxic A, oxic B, hypoxic, and anoxic categories, respectively (Table 3). Machine learning returned an overall prediction accuracy for organic enrichment status based on pore-water sulphide concentration of 0.77, with an accuracy of 0.91, 0.64, 0.40, and 0.85 for oxic A, oxic B, hypoxic, and anoxic samples, respectively. The three OTUs with highest importance scores for prediction of organic enrichment status were assigned to Sabatieria punctata , Capitella capitata , and Gunnarea capensis , respectively (Table 4); all these three OTUs showed preference for oxic B sediments. The OTU (OTU id: c94fc2ac2f0dc7c32b3decffc60bfc12) with highest importance score for predicting organic enrichment status had highest relative abundance in oxic B sediments.