Impact of submarine groundwater discharge on meiofaunal nematode community structure along the southwest coast of India

Submarine groundwater discharge (SGD) is a vital yet understudied driver of ecological change in coastal ecosystems, particularly in relation to sediment dwelling meiofaunal communities. This study investigates the impact of SGD on the richness, density, biomass, structural and functional diversity of free-living meiofaunal nematodes along the southwest coast of India. Field sampling was conducted across fifteen locations, including 11 SGD impacted and 4 unimpacted sites during three seasonal cycles for two years. Results showed significantly reduced nematode taxa richness, density, and biomass at SGD impacted sites compared to unimpacted sites, highlighting remarkable difference in community structure. The Co-occurrence network analysis revealed fragmented species interactions in SGD sites, in contrast to the denser and more stable networks at unimpacted sites. RLQ analysis demonstrated that SGD significantly structures nematode communities through environmental gradients, particularly salinity, dissolved oxygen, and grain size, shaping distinct trait associations. Finally, these findings underscore the importance of nematodes as sensitive ecological indicators and highlight the structuring role of SGD on coastal benthos.