Role of rotifers in microzooplankton community in a large monsoonal estuary (Cochin backwaters) along the west coast of India.

The distribution ecology of microzooplankton in the Kochi (Cochin) backwaters has been presented. Emphasis has been given to the micro-rotifers present in the environment, considering they were a hitherto ignored component of the microzooplankton in the past studies. Three seasonal samplings were carried out at six locations along the salinity gradients in the Kochi backwaters during the Pre-Monsoon (March), Southwest Monsoon (August), and Northeast Monsoon (December). A total of 48 species of microzooplankton were recorded, of which 35 were ciliates, 10 were rotifers, and 3 were heterotrophic dinoflagellates. The study also reports the swarm of a microzooplankton species from the Kochi backwaters, which was formed by a tintinnid ciliate, Tintinnopsis uruguayensis, during the Northeast Monsoon. Very high microzooplankton density (11,990 No. L-1), as swarm in the downstream location was associated with the mesohaline condition and high availability of food. Rotifers were the major component of microzooplankton in the limnohaline/oligohaline region, whereas ciliates dominated in the polyhaline/mesohaline region. Hence, in the present study, salinity appeared to be a major factor affecting the composition of the microzooplankton community in the Kochi backwaters. As rotifers have a wide food spectrum, they can feed on almost all components of the microbial food web, including small ciliates. They also share the same food spectrum with larger ciliates and crustacean nauplii. The present study, for the first time, recorded the importance of rotifers in the microzooplankton community in the plankton food web in the Kochi backwaters.