Symbiosis between the stramenopile protist Solenicola setigera and the diatom Leptocylindrus mediterraneus in the North Eastern Arabian Sea

Symbiotic associations between the diatoms and other organisms like cyanobacteria, flagellates etc. is less studied in Indian waters. Here, we report the occurrences of Solenicola setigera, a colonial protist found only in association with centric chain forming diatom Leptocylindrus mediterraneus. We observed these consortia in the surface waters (similar to 80-100 colonies L-1) of North Eastern Arabian Sea (NEAS) during the spring inter monsoon season of 2011 and were also observed in the water column (< 20 colonies L-1) up to 120 m depth. The consortium observed in the surface waters comprised single or few frustule with the protozoan colonies spread along the entire frustule, but those in the water column with the protozoan colony restricted to the central section of the frustule. Our observations suggest that Solenicola setigera is a heterotroph that grazes on pico and nanoplanktonic organisms thereby play an important ecological role in the North Eastern Arabian Sea ecosystem.