Vorticella and Colacium as epibionts of copepods in Pasig river, Philippines

The chitinous exoskeleton of copepods serves as a scaffold for microepibionts such as protozoa. Although copepods are highly cosmopolitan, their associated epibionts in the tropics are poorly known. This study presents the first account in the Philippines of the ciliate Vorticella on calanoid copepod Arctodiaptomus dorsalis and both Vorticella and the euglenoid Colacium on the cyclopoid copepods Thermocyclops crassus and Mesocyclops microlasius in the Pasig River. Infestation, however, was low at 0.83% (108 out of 13,039) observed copepods from four collection sites in January-May and July-December 2018. Interestingly, Vorticella and Colacium were frequently observed in cyclopoid than on calanoid copepods, predominantly on the urosome, thorax, cephalosome of copepodites and adult stages of copepods. Colacium was also found attached on the antennules, swimming legs, caudal rami and setae. Prevalence of epibionts was site-related; Vorticella being more abundant in waters near Manila Bay (Site 1) where high salinity, conductivity and total dissolved solids were recorded while Colacium was found more near Laguna de Bay (Site 4). Both were abundantly present in September and absent in May, due to increased inflow of seawater from Manila Bay. Nevertheless, overall low infestation resulted in neither significant spatial nor temporal variation of epibiosis in Pasig River, probably due to heavy loadings of wastewater from nearby tributaries, noticeable algal blooms, detachment of epibionts by predations and changes in water chemistry.