Abstract: The present study determined the trophic niches of nine gobiid fishes (Acanthogobius ommaturus, Amblychaeturichthys hexanema, Amoya chlorostigmatoides, Chaeturichthys stigmatias, Glossogobius giuris, Tridentiger barbatus, T. trigonocephalus, Ctenotrypauchen microcephalus and Trypauchen vagina) in Xiangshan Bay by analyzing stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of fish muscle samples. The δ¹³C and δ¹⁵N values of nine fish species ranged from -20.4‰ to -12.7‰ and from 6.7‰ to 14.5‰, respectively. The results of ANOVA analysis indicated that δ¹³C and δ¹⁵N values were significantly different between all examined species. The tropic levels of all examined species ranged from 2.33 to 3.46, which indicated that most of the nine gobiid fishes were secondary consumers in the Xiangshan Bay ecosystem. The convex hull area occupied by species in δ¹³C-δ¹⁵N niche space was employed to represent the tropical niche width for the nine gobiid fishes. Species which had greater niche widths, such as G. giuris, C. stigmatias and A. hexanema, were potentially feeding on a wide variety of prey species typifying a more generalized diet. Alternatively, species such as C. microcephalus, A. chlorostigmatoides and T. trigonocephalus exhibited lower niche widths, indicating that these species were likely feeding on a more specialized diet. In general, the degree of trophic niche separation among nine gobiid species was relatively low. There was intensely intraspecific competition between some gobiid species, such as C. microcephalus with T. vagina, and T. barbatus with T. trigonocephalus.

Key words: decomposition rate, plant mass, rising temperature, litter, habitat.