3.5 Environmental and sea cucumber core microbiota
A majority of ASVs in microbiota communities (on average 73.59 % ± 6.74 SD) were considered rare because of their low representation among samples (present in less than 30% of samples, as defined in Bjork et al., 2018). On average, 13.64 % (± 3.38 SD) of ASVs were considered as core (Table 4). Around 20.54 % of the core ASVs in the midgut or skin were not found in either of the environmental samples, although a small number of core ASVs were shared among the four sources (Figure 6). On top of that, 13 ASVs belonging to the core midgut microbiome were absent from sediment samples (Table S5). Indicator species also comprised on average 13.97 % (± 9.43 SD) of the microbial community (Table S6). The contributions of unique ASVs from different sources were different between the three sites. The highest contribution of unique ASVs in Starfish Bay and Tung Ping Chau originated from midgut samples, while more unique skin ASVs were found in Lai Chi Chong (Figure 6).