Community Structure of Microphytobenthos Associated with Mangrove Ecosystems Along the Southwest Coast of India

Microphytobenthos (MPB) plays an integral role in contributing to the productivity and sustenance of shallow marine ecosystem. MPB forms an integral component in the trophic structure of mangrove forest and its biogeochemistry. Microphytobenthos from three selected mangrove ecosystems (S1, Kannur; S2, Kochi and S3, Kollam) along the southwest coast of India was studied in detail for 1 year (2018-2019). Spatial and temporal (seasonal) variations in the community structure were addressed along with major environmental factors influencing the pattern of distribution. A total of 148 species of microphytobenthos under 58 genera were identified during the study. Diatoms (Bacillariophyceae) were the most abundant and diverse class of MPB present followed by Cyanophyceae, Dinophyceae and Euglenophyceae. The analysis of physicochemical parameters showed that salinity, temperature, sediment texture and nutrient characteristics were the major factors governing the community structure of MPB. Seasonally, maximum abundance was observed during monsoon and pre-monsoon with lesser diversity and extensive mats of cyanobacteria dominated by Oscillatoria spp. However, post-monsoon season with high nutrient concentration, increased salinity and more of sandy sediment texture supported diverse assemblage of diatoms. Dominant diatoms observed were Amphora spp., Diploneis sp., Navicula spp., Nitzschia spp., Pleurosigma sp. and Gyrosigma sp. Regionally, S3 Kollam was observed to be more diverse with the dominance of diatoms, whereas S2 Kochi observed lesser diversity with cyanobacterial dominance. Increased sediment grain size (sand similar to 68%) favoured diverse diatom assemblage at S3 resulting in an overall high MPB diversity of the area than S1 and S2.