Free-living marine nematode diversity from the Indian coasts
Free-living marine nematodes are ubiquitous in marine benthic ecosystems and play a key role in ecosystem processes. However limited information exists to date on free-living marine nematode community structure and diversity from biodiversity-rich tropical coastal environments. In this study, molecular tools based on the amplification, clone library generation and sequencing of the nematode 18S rRNA marker were employed to study free-living marine nematode community structure from two sites located in the Central West coast of India. Results based on the sequencing of 110 clones showed dominance of Enoplid and Chromadorid-like nematode 18S rRNA sequences, in addition to Monhysterid and Desmodorid-like sequences across study sites. Ptycholaimellus and Tripyloides-like nematode 18S rRNA sequences were abundant in clone libraries from the study sites. Based on morpho-taxonomic analysis, nineteen free-living marine nematode taxa were identified from both the study sites. Many of the identified taxa such as Ptycholaimellus sp., Tripyloides sp., and Terschellingia longicaudata were also detected in clone library sequences indicating that there was congruency between molecular and morphological approaches. At the same time, a sizeable number of sequences showed identity scores of only 87–96 % with published marine nematode 18S rRNA sequences available in databases indicating that the study sites harbour unreported species of marine nematodes. This finding was also supported by the presence of novel sub-clades based on phylogeny and OTU analysis where a sizeable number of singletons were detected. This study highlights the importance of including 18S rRNA marine nematode sequences in published nucleotide databases targeted specifically from biodiversity-rich tropical coastal regions so that it can ultimately improve our understanding of marine nematode community structure and diversity patterns, population genetics and nematode systematics.