Analysis of diversity of chromophytic phytoplankton in a mangrove ecosystem using rbc L gene sequencing

Phytoplankton forms the basis of primary production in mangrove environments. The phylogeny and diversity based on the amplification and sequencing of rbc L, the large subunit encoding the key enzyme ribulose‐1, 5‐bisphosphate carboxylase/oxygenase was investigated for improved understanding of the community structure and temporal trends of chromophytic eukaryotic phytoplankton assemblages in S undarbans, the world's largest continuous mangrove. Diatoms ( B acillariophyceae) were by far the most frequently detected group in clone libraries (485 out of 525 clones), consistent with their importance as a major bloom‐forming group. Other major chromophytic algal groups including C ryptophyceae, H aptophyceae, P elagophyceae, E ustigmatophyceae, and R aphidophyceae which are important component of the assemblages were detected for the first time from S undarbans based on rbc L approach. Many of the sequences from S undarbans rbc L clone libraries showed identity with key bloom forming diatom genera namely T halassiosira , S keletonema and N itzschia . Similarly, several rbc L sequences which were diatom‐like were also detected highlighting the need to explore diatom communities from the study area. Some of the rbc L sequences detected from S undarbans were ubiquitous in distribution showing 100% identities with uncultured rbc L sequences targeted previously from the G ulf of M exico and C alifornia upwelling system that are geographically separated from study area. Novel rbc L lineages were also detected highlighting the need to culture and sequence phytoplankton from the ecoregion. Principal component analysis revealed that nitrate is an important variable that is associated with observed variation in phytoplankton assemblages (operational taxonomic units). This study applied molecular tools to highlight the ecological significance of diatoms, in addition to other chromophytic algal groups in S undarbans.