낙동강 하구역에 출현하는 부유성 난 자치어의 종조성 및 초기 섭식생태

Abstract

In order to investigate the species composition of ichthyoplankton and feeding ecology of early stage in the Nakdong River estuary, Korea, ichthyoplankton were sampled monthly from September 2010 to August 2011. Among 11 taxa of pelagic eggs occurred in the study area, Nuchequula nuchalis, Konosirus punctatus,, Sciaenidae, Engraulis japonicus, and Cynoglossidae were dominant taxa during the study period, and these 5 taxa accounted for 95.0% of the total eggs. Among 43 taxa of fish larvae, gobiidae occurred in summer season (gobiidae-summer), Clupea pallasii, Engraulis japonicus, gobiidae occurred in spring season (gobiidae-spring), Konosirus punctatus, gobiidae occurred in winter season (gobiidae-winter), Sardinops melanostictus, Coilia nasus were dominant taxa, and these 8 taxa accounted for 95.0% of the total larvae. In this study, fish larvae showed temporal (spring, summer and late autumn, and winter) and spatial (inner and outer stations of estuary) separation in their occurrence. Feeding habits of fish larvae were examined for 10 dominant taxa (gobiidae-summer, -winter, and -spring; Engraulis japonicus; Clupea pallasii; Konosirus punctatus; Repomucenus sp.; Sardinops melanostictus; Coilia nasus; Liparis tanaki) in the order of number of individuals (except for the unidentified and in pre-larval stage species). The results showed that many fish larvae mainly preferred Copepoda for food. But gobiidae-spring preferred detritus for food; gobiidae-winter preferred Tintinnida for food; Coilia nasus preferred Cladocera for food; Konosirus punctatus preferred Rotifera for food. Most fish larvae showed ontogenetic changes in their feeding habits, including prey types and their sizes, which means the fish larvae could treat the bigger and highly energetic preys with their growth. Circadian feeding cycles of fish larvae in the Nakdong River estuary were distinguished one family from other families. Family gobiidae showed highest feeding incidence occurred at 18-21h, and the mean number of prey per individual followed the tendency of feeding incidence. Clupeidae showed bi-modal feeding incidence which had two peaks in late afternoon and midnight, and the mean number of prey per individual peaked in 18-19h. Meanwhile, Engraulidae fed only during the day, with peaks in feeding in the early morning and mid-afternoon. Limited resources, which include spatio-temporal resources and food resources, can cause competitions among the members of an ecosystem. There is a possibility that fish larvae occurred in the Nakdong River estuary face to some type of competition, so they showed different temporal and spatial occurrence patterns and trophic separation with different main prey items and/or subsidiary prey items to avoid inherent competitions.