Biodiversity of Planktonic Copepods in the Lanyang River (Northeastern Taiwan), a Typical Watershed of Oceania

Abstract

To evaluate the environmental status of a typical Oceania watershed in Taiwan, zooplankton samples were collected bimonthly along the Lanyang River (NE Taiwan) at 9 different stations including 1 estuarine and 8 freshwater stations during 10 sampling campaigns from June 2004 to Dec. 2005. Upstream stations showed lower chlorophyll a and temperature values than downstream stations; the highest chlorophyll a concentration was found in the estuary at all times. We identified 21 copepod species, belonging to 4 orders, 12 families, and 20 genera in total. Eleven species were recorded only once among all samples. The Calanoida was restricted to samples from the estuary. The Poecilostomatoida was only recorded from the estuary and the Lanyang Bridge station. The Harpacticoida was only recorded from the estuary, Lanyang Bridge, and Tsu-Keng River stations. At 2 mid-section stations, no copepods were found. The upstream station showed lower abundance, species number, species richness, and evenness and diversity indices than the downstream and estuarine stations. The estuarine station provided the highest copepod abundance (3410.05 individuals/m3) and species number (12 species/station) in Aug. 2004 when the waters showed the highest salinities (37 psu), indicating the marine origin of the diverse biota. Among all samples, there were no significant differences in the abundance, number of species, or indices of richness, evenness, and diversity among sampling months. In contrast, our analysis clearly showed a succession in abundance and species composition among sampling months. At the estuarine station, copepod abundances were significantly positive correlated with salinity (r = 0.880, p = 0.001). Numbers of species were significantly positive correlated with chlorophyll a (r = 0.790, p = 0.007), salinity (r = 0.780, p = 0.008), and copepod abundance (r = 0.785, p = 0.007). Copepod abundances were mainly affected by intruding seawater, but there was no interaction with the month of sampling.