진주만의 내·외측에서 채집된 어란, 자치어 및 유어의 종조성 및 군집구조

Abstract

The Jinju Bay is surrounded by Sacheon-si, Hadong-gun, and Namhae islands, which are located in the middle of the Korean Strait. In addition, this bay is semi-enclosed which is highly influenced by Namgang Dam located in the north. This bay has been known as spawning and nursery grounds of various species, and has been used as a shellfish farm for a long time because it is less influenced by wind wave from the open sea. On the other hand, about 25% of the bay is composed of intertidal zone, which may increase the accumulation of organic pollutants due to urban and human activities. This area needs to be managed to maintain environmental health performance and major ecological functions. Therefore, we investigated the environmental characteristics inside and outside of the Jinju bay and the changes of species composition of fish eggs, larvae, young fish and adult fish. In addition, we studied the functions as spawning and nursery grounds of the bay of comparison of environmental characteristics between inside and outside of the bay. As a result of inside and outside environmental characteristics of Jinju bay, bottom water temperature and salinity were different. Fluctuations in bottom water temperature were larger inside of the bay (7.1–24.0 ℃) than outside of the bay (8.3–23.2 ℃). A thermocline was formed from April to August due to many isotherms between the surface and bottom layer. Salinities were consistently lower inside of the bay than outside of the bay around the year with the highest salinity observed in June 2016 (Inside of the bay, 32.7 psu; outside of the bay, 33.1 psu) and the lowest in July 2016 (30.2; 31.2 psu). The lower salinity in July was due to the increase in the amount of water discharge from Namgang Dam. Therefore, the results showed that the water of surface layer flow from inside to outside of the bay while bottom layered seawater flowing inversely. Fish eggs and larvae were collected duaring every month from April 2015 to March 2016 using an ichthyoplankton net from inside of the bay (stations 1, 2, and 3) and outside of the bay (stations 4, 5, and 6 located between Changseon and Saryang islands). The samples were classified based on morphological characteristics and, molecular analysis was performed to amplify the mtDNA COI region. As a result, 28 species, 17 families and 5 orders were collected, and 25 species were collected inside of the bay, while 20 species were collected outside of the bay. The result of cluster analysis show that inside and outside of the bay were divided into two groups. The species, contributed to distinguishing between the inside and outside of the bay, were Thryssa kammalensis and Konosirus punctatus. The bottom water temperature of lower layer inside of the bay was maintained higher than that outside of the bay for 6 months (April to September). As a result, the eggs of three species (Sillago japonica, Acanthopagrus schlegelii, and Platycephalus indicus) were collected two months earlier and the eggs of Pennahia argentata, Zebrias fasciatus, and Pagrus major were collected one month earlier inside of the bay. During the survey period, a total number of eggs inside of the bay were higher than outside of the bay. However, exceptionally, the number of individuals in August have higher outside of the bay and it is estimated that the fresh water discharge from the Namgang Dam influence. A total of 28 eggs were collected in this study and among them, 16 species including A. schlegelii and P. major were recorded for the first time in Jinju bay. In terms of larvae, 40 species, 19 families and 5 orders were collected, and 35 species were collected inside of the bay, while 28 species were collected outside of the bay. The most dominant species of fish larvae was Engraulis japonicus both inside of the bay (70.9%) and outside of the bay (77.9%). The next dominant species were S. japonica and Omobranchus elegans. The number of species which were collected only inside of the bay was 12 species, and 5 species were collected only outside of the bay. The eggs and larvae collected from inside and outside of the bay were 52 species and 41 species, respectively. As a results, more various species found to spawn inside of the Jinju bay. Fish samples were monthly collected using a shrimp beam trawl at each one station inside of the bay and outside of the bay between December 2014 and November 2015. As a result, 15,715 ind./km2 belonging to 63 species, 40 families and 11 orders were collected inside of the bay and 28,839 ind./km2 of 65 species, 42 families and 10 orders were collected outside of the bay. The number of species were similar between inside and outside of the bay, but the number of fish individuals outside of the bay was higher than inside of the bay. The most dominant species was Nuchequula nuchalis, are the occurrence frequency showed similar between inside (26%) and outside of the bay (27%). The next dominant species were T. kammalensis (18%) and Zoarces gillii (16%) inside of the bay and Liparis tanakae (17%) and T. kammalensis (9%) outside of the bay. In the spring and autumn, the dominant species inside and outside of the bay were the same as Z. gillii and N. nuchalis. However, the dominant species were different in winter and summer, Pleuronichthys cornutus and N. nuchalis inside of the bay, and L. tanakae and T. kammalensis outside of the bay. The number of young fish inside of the bay (40 species; 33% of total number of individuals) are more than outside of the bay (47 species, 52%), indicating that more various species growth inside of the bay. Young fish of P. cornutus, Z. gillii, and Hemitripterus villosus were collected intensively inside of the bay in March to June, meanwhile, young fish of L. tanakae (in March to May) and Pennahia argentata (in September to November) were collected outside of the bay. The egg, larvae, young fish and adult fish of 95 species were collected from inside and outside of the Jinju bay, and then we could know the location and timing of spawn and early growth of each species. The eggs and larvae of E. japonicus were consistently appeared inside and outside of the bay except for the low temperature period from January to March. Spawning ground of S. japonica was concentrated in June inside of the bay and outside of the bay in August, and after that they move to outside of the bay to grow. The P. argentata spawning and hatching inside of the bay from June to August and they used outside of the bay to grow in October - November. The A. schlegelii (in April to Jun) and P. indicus (in Jun) used inside of the bay as a spawning ground. Jinju bay was identified as a major spawning and nursery grounds for fish species living in the southern coast such as A. schlegelii, P. argentata, P. indicus, S. japonica, Kareius bicoloratus, P. cornutus, and L. tanakae. Each species used inside and outside of the bay as spawning and nursery grounds according to their characteristics. Therefore, ecological management of inside and outside of the Jinju bay was necessary for the management of marine fish resources in the central sea of the South Sea.