Composition, Abundance and Distribution of Rotifers in the Pasig River, Philippines

Pasig River is situated in the highly urbanized area of Metropolitan Manila. Rotifer composition, abundance and distribution were observed by analyzing plankton samples from five sites along the Pasig River from June to September 2007. Physical-chemical parameters were also measured for each sampling site. Thirty rotifer species had been identified and monthly differences in species number, abundance, temperature, and salinity have been observed. Variations in Shannon-Wiener diversity as well as dissolved oxygen (DO), temperature, Secchi Disc transparency and salinity were not noted between sampling sites. Lowest densities (54.55 indv/m 3 ) and DO values (range: 0-5.18 ppm) were seen in the area near the mouth of the San Juan River while highest density was noted in the vicinity of the Napindan Bridge near Laguna de Bay (259.94 indv/m 3 ). Changes in the number of rotifer species and abundance per month were related to the levels of dissolved oxygen, temperature and salinity. Pollution-tolerant and indicator species such as those from the genus Brachionus, Keratella, and Filinia were among the most common and abundant rotifers observed validating the eutrophic state of the river and its headwater.