Spatial and seasonal variations in fish assemblages of the Yangtze River estuary

Abstract

Summary This study aimed to test the hypothesis that biotic influences play a role in determining estuarine fish assemblages. Thus the mechanisms that regulate the observed spatial niche segregation between fish species with morphological and ecological similarities within estuaries were investigated. Fishes were sampled seasonally at 30 stations along an entire salinity gradient of the Yangtze River estuary from spring 2010 to winter 2011, using bottom trawling (10 mm mesh size in the cod end). A total of 62 species belonging to 28 families were collected. Marine migrants (21) and estuarine species (19) dominated the assemblage and accounted for the highest abundances (marine migrants = 42.5%, estuarine species = 38.3%), with the marine migrants having the highest biomass (57.2%). Canonical correspondence analyses indicated that chlorophyll a, salinity, temperature, and geographic distance were the four main variables influencing the occurrence of fishes within the system. A stable fish assemblage in the upper zone during the wet season (spring and summer) was more obvious than in the dry season. The Pianka index showed a clear spatial segregation in four pairs of tonguesoles species (Cygonobius), and in most pairs of gobiids (Gobiidae), and a high degree of overlapping (>0.60) in only four pairs of gobiid species during the wet season. However, according to the results of the null model the observed segregating or pattern sharing was not caused by interspecific competition.

The Non-stationary Environmental Effects on Spawning Habitat of Fish in Estuaries: A Case Study of Coilia mystus in the Yangtze Estuary

“…The non-stationary effects of abiotic variables were reflected by the spatially varying relationship between the independent variables and dependent variables (Li et al, 2018). Both SST and SSS represented the primary habitat environment in defining C. mystus spawning habitat Shi et al, 2014). In the reproductive season, adults of C. mystus would spawn to the brackish water with salinity from 0.14 to 7.51 and temperature of 18-28 • C in the Yangtze Estuary (Ni et al, 1999;Zhuang et al, 2006;Ding, 2011).…”

“…The distribution of fish spawning habitat is usually determined by the adaptation of reproductive physiology and species response to the surrounding environmental conditions (Gallego et al, 2007;Zorica et al, 2013;Gonzalez-Irusta and Wright, 2016;Reglero et al, 2017). The spawning distribution could be influenced by various environmental factors, e.g., temperature, salinity, topography (Opdal, 2010;Dumont et al, 2011;Shi et al, 2014). There is evidence that compared with adults, the early life history stages of fish species seem to be more sensible and vulnerable to the variations in the environmental conditions (Portner and Farrell, 2008).…”