Integrating spatial and temporal patterns of free‑living nematodes with physical and chemical environmental traits: implications for coastal ecological monitoring

Relating biological patterns to the physical environment is increasingly explored in current period of global biodiversity crisis and attempts to identify ecological status. Free-living marine nematodes (FMN) were proposed as ecological indicators, although often under approaches based on developing synthetic indexes of environmental quality, contextually neglecting the crucial issue of their spatial and temporal variability in abundance and diversity, and its relationship with environmental drivers. This study, carried out on the north-eastern coast of India as a region subject to various anthropogenic activities, assessed the patterns of FMN structure, richness, equitability, trophic guilds, life strategy and morphological traits at three sites, three times over 1 year, two beach levels and three sediment layers upto 15 cm deep. Nematode patterns were then related to the amount of sand, silt and clay, organic carbon, and salinity. Each FMN characteristic was largely variable in time and space, being organic carbon and salinity the environmental variables most correlated to such patterns. Monitoring designs suited to capture such variability are recommended to improve the use of FMN as bioindicators. Just relying on unidirectional data to define environmental status is questioned, while it is proposed to consider the Effect of Positional Constraints when assessing ecosystem health.