동해 연안해역에 출현하는 저어류 군집의 섭식관계와 영양분할

Abstract

The present study investigated assemblage structures, feeding relationship and trophic partitioning of demersal fishes using fish samples caught by a gill net during warm (Jun.~Aug.) and cold (Jan.~Mar.) seasons in the northern, middle and southern coastal waters of the East sea in 2018. During the study period, a total of 48 fish species from 21 families and 7 orders, a total of 1,386 individuals and 229,319.2g biomass were collected. In terms of abundance (number of individuals), the dominant fish species were Cleisthenes pinetorum, Pleuronectes herzensteini, Glyptocephalus stelleri, Gymnocanthus herzensteini and Gadus macrocephalus. The fish assemblages showed distinct latitudinal variables with occurring 27 species, 378 individuals and 89,856.7g at the northern coastal water, 20 species, 845 individuals and 82,431.9g at the middle coastal water, and 21 species, 163 individuals and 57,030.6g at southern coastal water, respectively. The result of cluster analysis revealed that the fish assemblages were significantly clustered in the middle and the northern coastal waters at 30% level of similarity, but that of the southern coastal water differed from other two study areas. The result of the stomach content analyses of dominant fish species inhabiting the coastal waters of East sea showed each different dietary patterns, depending on fish species, coastal waters (i.e. latitude) and seasons, and the factors influencing these differences were the primarily fish species and secondarily latitude. The stomach contents analysis also showed the result of the diet resources usage features of each fish species and their partitioning or sharing that resources between them. According to this results, even though the demersal fishes in the East sea appeared at 3 regions (northern, middle, southern) at the same time, they were able to coexist by using different prey resources each other. The composition of diet organisms estimated from the stomach contents of predators were divided distinctly at each regions and seasons, but the diet organisms in the southern station were overlapped highly between each seasons. Among the dominant fish species, Lophius litulon preyed mainly on Teleostei and G. macrocephalus, G. herzensteini and C. pinetorum preyed evenly on Teleostei, Cephalopoda, Caridea and Mysidacea. On the other hand, G. stelleri and Lepidopsetta bilineata preyed mainly on Polychaeta and Alcichthys elongatus, Hexagrammos otakii and Pleuronectes herzensteini preyed on not only Amphipoda but also a variety of benthic invertebrate animals. From these differences diet organisms of each fish species, the demersal fish assemblages in the East sea can be divided into 5 predator guilds and 3 sub-guilds. Also diet organisms consumed by all fishes in the East sea can be divided into 5 prey guild depending on similarity. Shade plot analysis integrating these divided guilds from both predator and prey offered the result that predator-prey relationship of predator and prey can be shown more clearly. Trophic niches of main dominant fish species estimated from carbon and nitrogen stable isotope were different at each fish species, and these differences were reflected from the result of feeding environments depending on the differences of inhabiting type (pelagic, semi-pelagic, benthic) of each fish species. According to such different trophic niches, dominant fish species can be divided into 6 trophic groups via Cluster analysis and nMDS ordination from stable isotope values, indicating different trophic niches in each trophic group. The results of trophic niches (i.e. trophic level) of main dominant fish species estimated from both the stomach contents and nitrogen stable isotope showed that most of fish species have similar trophic levels, but some of them have differences in trophic levels due to the different periods of assimilation for consumed preys. Estimated trophic levels of Platycephalus indicus, L. litulon, G. macrocephalus, G. herzensteini, C. pinetorum, H. otakii were relatively high, whereas Clupea pallasii, Thamnaconus modestus, Scomber japonicus, Ditrema temminckii represented lower trophic level. In conclusion, the possibility to analyze the food web structure of middle and southern coastal waters in the East sea was presented by integrating both predator-prey relationship estimated via stomach contents analysis and trophic niches estimated via stable isotope analysis. This results will be able to present a useful method for estimating more accurate food web structure in marine ecosystem. Nevertheless, in this study, there were difficulties to analyze the ecological features of each fish species and food web structure more accurately because of the lack of data about abundances of prey organisms and their stable isotopic values. Thus, additional studies to make up for supporting these data is needed. The results of this study presented the important baseline data and new direction of study for understanding marine ecosystem and researching the impact of marine ecosystem caused by outside influences such as climate change and change of marine environments in the future. Furthermore, the results of this study will be able to present an important approach to understand the function of the coastal waters in Korea, and to make a big contributing for improving ecosystem modelling to analogize the changes of ecosystem from a long-term perspective.