Factors regulating proliferation and co-occurrence of loricate ciliates in the microzooplankton community from the eastern Arabian Sea

Abstract

Ciliates are highly developed and diverse eukaryotes belonging to the microzooplankton community; they exhibit a wide distributional range and are a crucial component of the microbial food web. The current study addresses the species aggregation of ciliates, which is rare and underreported, from the Indian waters. The aggregation was dominated by coexisting species such as Amphorides quadrilineata and Salpingella faurei during 2018 (45-95%), whereas Dadayiella ganymedes and Helicostomella subulata predominated in 2003 (40%), with both aggregations occurring during late summer monsoon (September) in the region. The species environmental correlation revealed that salinity and chlorophyll a, especially the nanoplankton fraction, were significant factors responsible for the exceptional abundance and community structure. The pattern of association with the distinct lorica oral diameter (LOD) of the coexisting species exhibits an upper range of 28-32 �m (A. quadrilineata and D. ganymedes) and a lower LOD range of 15-17 �m (S. faurei and H. subulata), delineating a niche based on resource spectrum and revealing why certain species successfully predominate in utilizing the available resources. Although such events have received sporadic attention, the recurrence of aggregation comprising strategic coexistence of species indicates the status of the ecosystem and argues for future monitoring to better understand the dynamics of the region.