Potential indicator taxa: Nematoda and Polychaeta
There were 175 Nematoda OTUs and 38 Polychaeta OTUs in the
OTUBM table. Polychaeta are commonly used for
morpho-taxonomic analysis for benthic impacts of fish farming; however,
interestingly here we found a much stronger correlation between Nematoda
and pore-water sulphides than Polychaeta. The correlation between
Nematoda OTU richness and pore-water sulphide concentration was -0.86,
whereas that between Polychaeta OTU richness and pore-water sulphide
concentration was -0.38 (Figure 4). The GLMM analyses showed a positive
relationship between Nematoda OTU richness and distance from cage edge,
but no relationship was identified between Polychaeta OTU richness and
distance (Figure S4). Across all samples, Nematoda OTU richness
increased along distance from cage edge. Within each farm, the
correlation coefficients between Nematoda OTU richness and distance from
cage edge varied from 0.55 to 0.86 (Figure S5).
Capitella polychaetes were found in both morphotaxonomic
macrofaunal data and eDNA metabarcoding data; they were present in 29/42
and 25/42 of sampled stations as revealed by macrofaunal and eDNA
metabarcoding analyses, respectively (Figure 5). Presence/absence ofCapitella at each station of BS, MI and VP agreed between
macrofaunal and eDNA data. There was one station at MR (90 m) whereCapitella was present in macrofaunal data but not eDNA data;
conversely, there was one station at BI (60 m) where Capitellawas present in eDNA data but not macrofaunal data. Patterns at PP were
markedly different: macrofaunal analyses found Capitella at six
stations, with a proportion in Polychaeta individuals ranging from
0.38% to 82.5% among stations, whereas Capitella were present
only at two stations in eDNA data. Capitella was not detected at
reference stations in either macrofaunal or eDNA datasets. The
correlation coefficient between pore-water sulphide concentration and
relative abundance of Capitella in eDNA data was 0.28 (Figure 4)