After decades of strict pollution control and municipal sewage treatment, the water quality of the Tanshui River increased significantly after pollution mitigation as indicated by the River Pollution Index (RPI). The pollution level of the estuarine region decreased from severe pollution to mostly moderately impaired. The most polluted waters are presently restricted to a flow track length between 15–35 km relative to the river mouth. From July 2011 to September 2012, four surveys of fish and benthic macroinvertebrates were conducted at 45 sampling sites around the Tanshui River basin. The pollution level of all the study area indicated by the RPI could also be explained by the Family Biotic Index (FBI) and Biotic Index (BI) from the benthic macroinvertebrate community, and the Index of Biotic Integrity (IBI) of the fish community. The result of canonical correlation analysis between aquatic environmental factors and community structure indicated that the community structure was closely related to the level of water pollution. Fish species richness in the estuarine area has increased significantly in recent years. Some catadromous fish and crustaceans could cross the moderate polluted water into the upstream freshwater, and have re-colonized their populations. The benthic macroinvertebrate community relying on the benthic substrate of the estuarine region is still very poor, and the water layer was still moderately polluted.

We used the mitochondria DNA COI (cytochrome c oxidase subunit I) sequence as a genetic marker to analyze the population genetic structure of two species of freshwater copepods, Neodiaptomus schmackeri (Poppe and Richard, 1892) and Mongolodiaptomus birulai (Rylov, 1922) from Taiwan. Four populations with 51 individuals of N. schmackeri and five populations with 65 individuals of M. birulai were included. We compared the nucleotide sequences of a 635-bp fragment of the COI gene of N. schmackeri and a 655-bp fragment of the COI gene of M. birulai, and eight and 14 unique haplotypes were recorded, respectively. Tseng-Wen reservoir and Wu-San-Tao reservoir are linked by a channel, and the gene flow between them was unrestricted (F_st = 0.058; N_m = 4.04; F_st, population differentiation parameter; N_m, the number of succesfull migrants per generation); the gene flow between all other populations of both species was restricted (F_st = 0.4–0.99; N_m = 0–0.37). Based on the COI gene diversification pattern, we suggest that most populations of N. schmackeri and M. birulai are isolated from each other. According to the neighbor-joining tree and the minimum spanning network (MSN), the species have similar metapopulation genetic structures. Genetic distance was not found to be correlated with geographical distance. The genetic diversification pattern was not shown to be comparable with geographical isolation owing to long-distance separation. The genetic structure of the present populations may result from serial extinction and redistribution of the populations formed in each reservoir relative to time. Human activity in the reservoirs with regards to water resource management and the fishery industry also exerts an effect on population redistribution.

In the mountain area of Taiwan, we investigated 10 subpopulations of Neutrodiaptomus tumidus Kiefer 1937 living in isolated alpine ponds or lakes. We used mitochondrial DNA cytochrome C oxidase subunit I (COI) sequence as molecular marker to investigate the population genetic structure and their phylogeographical relationships.