Choreotrich ciliate tintinnid (Protozoa: Ciliophora) in a tropical meso-macrotidal estuary, eastern part of India

An annual community structure of the loricate ciliate tintinnids, the ubiquitous planktonic protist, was analysed from nine sampling sites (n=108) of diverse environmental stresses along the Hooghly (Ganges) River Estuary, eastern coastal part of India. The agglomerated genus Tintinnopsis sp., was dominated among the 32 identified tintinnid species (3 core, 12 seasonal and 17 occasional species) contributing ∼62% of total tintinnid population. The size-class distribution of lorica oral diameter ranges between 9 and 22 μm for majority of the tintinnids (∼71%) which provides relevant information on the ecological characteristics for the species assemblages. The maximum species diversity for tintinnid (H′=1.71) during postmonsoon (February, 2014) has been attributed by high numerical density of phytoplankton dominated by diatoms (4400 cells l−1,H′=3.41) at the site Gangasagar, mouth of the estuary. The large-sized tintinnids Tintinnopsis cylindrica (lorica length = 262.8 μm; lorica oral diameter = 65 μm) and T. radix (lorica length = 278.6 μm; lorica oral diameter = 62 μm) belonging to family Codonellidae, formed successful dominant group (>50% of the total) in this estuarine ecosystem. The core species abundance (Tintinnopsis beroidea, Tintinnidium primitivum and Leprotintinnus simplex) shares ∼57% of total tintinnid population followed by seasonal (35%) and occasional species (8%), characterized by their eurythermal and euryhaline nature. As revealed from the results of cluster analyses, majority of the tintinnids formed an individual functional group, exhibiting similar assemblages in species distribution. The Canonical Correspondence Analysis map (CCA) revealed a clustering of core species with the phytopigment (Chlorophyll a) and dissolved oxygen which were found to be the most important causative factors controlling the distribution and seasonal patterns of tintinnids. Well-defined tintinnid assemblages are evident representing the fingerprint of the specific ecological zone of Hooghly estuary, characterized by a set of environmental variables.