Horizontal distribution of nematode communities in a seasonally-hypoxic enclosed sea (Omura Bay, Japan)

Abstract

Habitat heterogeneity is one of the major factors shaping community structure and diversity of many fauna. The present study aimed to reveal the influence of habitat heterogeneity on the nematode community structures and diversity in a seasonally hypoxic bay (Omura Bay of Nagasaki in Western Kyushu, Japan). The severity of hypoxia varies typically along north-south axis of the bay, which is intensified southwardly. Nematode abundance and diversity were highest in the northern site than the other sites, and nematode communities were clustered into three groups by sampling site. There were significant differences in composition (Two-way ANOSIM, Rho = 0.726,p < 0.05) and in feeding types (Two-way ANOSIM, Rho = 0.589,p < 0.05) among the groups. Organic matter content alone was the best predictor for the shift in nematode compositions (BIOENV procedure, Correlation = 0.666,p < 0.05), whereas the combination of salinity and DO correlated well with the shift in nematode feeding types (Correlation = 0.568,p < 0.05). These findings strongly suggest that the diversity and the structures of nematode assemblages were strongly affected by the habitat heterogeneity in terms of seasonal DO availability, salinity change and persistent food availability (organic carbon accumulation) over the surface sediment of the bay.