Zooplankton Fluctuations in the Surface Waters of the Estuary of a Large Subtropical Urban River

Pei-Wen Lee,Shih-Hui Hsiao,Jiang-Shiou Hwang,Chi Chou,Li-Chun Tseng

doi:10.3389/fevo.2021.598274

Abstract

The Danshuei River has a third largest catchment area and third longest in Taiwan. It flows through the capital, Taipei, and more than six million people live within its catchment area. Its estuary is characterized by a highly variable chemical and physical environment that is affected by the interaction of inland freshwater runoff with wastewater, and toward the coast is also influenced by the China Coastal Current and the Kuroshio Current. By collecting zooplankton bimonthly in 2014 from the surface layer (0–2 m depth) at five sites in the estuary, we were able to demonstrate that the composition of the zooplankton, and particularly its copepod fraction, varied significantly among sampling stations and months, thereby revealing seasonal succession. Fourteen higher taxa or other categories of zooplankter were identified, with the following being most common taxa: Decapoda, Copepoda (including Calanoida, Cyclopoida, and Harpacticoida), and “other larvae.” The Copepoda comprised 44 taxa (including eight only identified to genus) belonging to 3 orders, 17 families, and 29 genera, the five most abundant of which wereBestiolinan. sp. (undescribed),Corycaeusspp.,Parvocalanus crassirostris,Acartiasp., andParacalanus parvus. The highest and lowest copepod abundances were recorded in July (2557.88 inds. m–3) and January (1.3 inds. m–3), respectively. Observed changes in abundance of many kinds of copepod appeared to be significantly related to changes in physico-chemical parameters (e.g., salinity, temperature, pH, and dissolved oxygen concentration). Cluster analysis confirmed the existence of distinct copepod communities, each characterized by a preference for a different set of environmental conditions. Our comprehensive literature review of the copepod biodiversity of Taiwan’s major rivers for comparison with similar data compiled for other estuaries in the world, the first time such a review has been compiled, shows that 32 copepod taxa have been recorded from the brackish and freshwater parts of the Danshuei River. They represent 58.2% of the total number of brackish- and freshwater copepod species in Taiwan, and five of them have so far only been recorded in the Danshuei River: the calanoidsAcartiella sinensisandPseudodiaptomus forbesi, the cyclopoidsOithona fragilisandOithona simplex, and the harpacticoidTachidius(Tachidius)discipes.

Highlights

Estuaries are transitional zones between rivers and the sea (Meire et al, 2005; Wang et al, 2007; Telesh and Khlebovich, 2010; Shan et al, 2013)
Tide tables for the Danshuei River issued by Taiwan’s Central Weather Bureau (Figures 3A–F) report tidal heights relative to the local annual mean water level
Salinity and temperature (Stepien et al, 1981; Milione and Zeng, 2008), intruding seawater, rainfall, and freshwater runoff (Yu, 2005; Dahms et al, 2012, 2013; Tseng et al, 2013), tidal movements (Shih, 2007), turbidity (Islam et al, 2005), and assorted physico-chemical parameters of river water (Khanna et al, 2005; Kumar et al, 2015) are known to affect the community composition of both phytoplankton and the zooplankton, the present results show that intruding seawater is the most important transportation vector in the Danshuei River estuary

Summary

Introduction

Estuaries are transitional zones between rivers and the sea (Meire et al, 2005; Wang et al, 2007; Telesh and Khlebovich, 2010; Shan et al, 2013). The turbidity of the river water increases, and salinity decreases, in the upstream direction (Elliott and McLusky, 2002), the gradient in salinity being caused by the interplay of denser seawater and overlying riverine freshwater (Hwang et al, 2010; Telesh and Khlebovich, 2010). Estuaries provide nursery grounds for larvae and juveniles of invertebrates and fish and important foraging grounds for migratory birds (Shan et al, 2013). Terrestrial nutrient runoff into estuaries (Godhantaraman and Uye, 2003) nourishes spawning and fishing grounds that are inhabited by many commercially important species of fish and shellfish (Shan et al, 2013)

Methods

Results

Discussion

Conclusion