Seok Nam Kwak

Length–weight relationships and reproductive characteristics of the crowned seahorse (Hippocampus coronatus) in eelgrass beds (Zostera marina) of Dongdae Bay, Korea

Abstract This study provides novel information regarding the length–weight relationships (LWRs) and reproductive characteristics of the crowned seahorse (Hippocampus coronatus) living along the southern coast of Korea. Specimens of H. coronatus were collected from an eelgrass bed in Dongdae Bay, Korea, during September 2006–August 2007. In total, 133 specimens were collected (76 females, 57 males) and their lengths ranged from 2.41 to 9.31 cm and 2.41 to 9.32 cm for females and males, respectively. No significant difference was observed between the sex ratio of specimens collected in this study and the theoretical 1:1 ratio (χ2-test, P > 0.05). All LWRs were highly correlated (r2 > 0.941, P < 0.001), and the overall slopes of the length–weight regressions were 3.067 for females, 2.808 for males and 2.955 for both sexes. Size at first sexual maturity was 6.93 and 7.33 cm in length for females and males, respectively. Monthly changes in the gonadosomatic index (GSI) indicated that the spawning period was from June to November. Total number of eggs ranged from 56 to 163 with mature eggs from 4 to 56, and the number of brood in the pouches of males ranged from 12 to 46.

Abundances and feeding habits of Hippocampus coronatus in an eelgrass (Zostera marina) bed of Dongdae Bay, Korea

해마 (Hippocampus coronatus)는 큰가시고기목 (Gasterosteiformes) 실고기과 (Syngnathidae)에 속하는 어종 으로 전 세계적으로 약 54종이 알려져 있다. 해마류 (Hippocampus sp.)는온대및열대해역의수심이얕은연 안해역에서 주로 서식하며, 산란기에 암컷이 수컷의 육 아낭에 알을 넘겨주어 수컷이 새끼를 출산하는 특이한 산란 방식을 가지고 있어서 아주 중요한 생태적 지위를 차지한다 (Foster and Vincent, 2004; Kim et al., 2005; Kwak et al., 2008) 최근 들어 해마류는 관상용 및 한약재의 재료로 주로 이용되고 있으며 인간의 무분별한 연안개발로 인해 그 서식지가파괴되고있는실정이다 (Vincent, 1996; Lourie et al., 1999). 이에 따라 해마류는 2002년부터 CITES

Feeding relationships among juveniles of abundant fish species inhabiting tropical seagrass beds in Cockle Bay, North Queensland, Australia

Dietary analysis was conducted on juveniles of 10 numerically abundant fish species inhabiting tropical seagrass beds in North Queensland, Australia. Gammarid amphipods were consumed by all of the species, but their contribution to the diet of each varied. Crab larvae and copepods contributed to the diets of Leiognathus bindus, Pranesus endrachtensis and Stolephorus sp.; polychaetes and isopods were consumed by Sillago maculata burrus, Lethrinus sp., Pelates sexlineatus and Siganus canaliculatus; and Favonigobius reichei, Coris caudimacula and Arothron manilensis fed on bivalves. Seagrass and gastropods were rarely ingested by most of these fishes, but made a moderate contribution to the diet of A. manilensis. With the exception of L. bindus, the diet of each species was correlated with size: smaller species consumed copepods, crab larvae and gammarid amphipods, while larger species ate polychaetes, bivalves, isopods and gastropods. Non-metric multidimensional scaling (MDS) ordination plots emphasised the variation in dietary composition between species, and showed that this was often correlated with mouth length and width of the fish—for example, species with larger mouth dimensions tended to have broader diets. These interspecific differences in dietary composition increase the number of food resources available to these fishes, thereby reducing the potential competition for resources within the fish community.

The Effect of Ocean Acidification on Early Growth of Juvenile Oliver Flounder (Paralichthys olivaceus): in situ Mesocosm Experiment

An in situ mesocosm experiment was designed to investigate how exposure to ocean acidification by increased carbon dioxide affected the growth of juvenile oliver flounder (Parali- chthys olivaceus). A total of 447 individuals were reared in the mesocosm experimental devices deployed at sandy-muddy bottom in the southern coast of East Sea for 43 days and divided into two groups: treatment group (223 individuals, 6.32±0.75 cm, high-CO2 environment) and control group (224 individuals, 6.34±0.84 cm, natural CO2 environment). The average values of pH and CO2 concentration in the treatment device were 7.63±0.13 and 1660±540 μatm, respectively, while those in the control device were 8.07±0.05 and 514±65 μatm, respectively. There was no signi- ficant difference in mortality rate between treatment and control group, and the mortalities in two groups gradually decreased during the study period. But, the increase of size and weight of juvenile oliver flounder was higher in control group than treatment group, i.e., weight gain or growth rate was higher in control group. These results suggested that high CO2 environments could have a significant negative influence on the early growth of juvenile oliver flounder.

Feeding Relationships among Six Seagrass-associated Fishes in the Northeastern Gwangyang Bay, Southern Korea

We conducted dietary analyses of six seagrass-associated fish species inhabiting northeastern Gwangyang Bay, Korea. These six species consumed a variety of benthic invertebrates and teleosts, but their preferences for different food resources varied. Although all species consumed crustaceans, the contributions of different crustacean taxa differed among the species’ diets. Caridean shrimps and crabs were a significant part of the Hexagrammos agrammus and H. otakii diets, respectively, while amphipods were consumed mainly by Sebastes inermis. Caridean shrimps and prawns were abundant within the Lateolabrax japonicas diet, but were not common prey resources for Pseudopleuronectes yokohamae or S. schlegelii. Polychaetes and ophiurids were ingested by P. yokohamae, and the former prey taxon also made moderate contributions to the diets of H. agrammus and L. japonicus. With the exception of P. yokohamae, the diets of all species included teleosts. Teleosts contributed the largest proportion of the S. schlegelii diet, followed by the S. inermis and L. japonicas diets; however, H. agrammus and H. otakii rarely consumed teleosts. Non-metric multidimensional scaling (nMDS) ordination plots and permutational analysis of variance (PERMANOVA) revealed the variation in dietary composition among species and the contributions of each prey taxon. These interspecific differences in diet increase the range of food resources available to these fishes, thereby reducing competition for resources within the fish community in this region.

Ecological Characteristics of the New Recorded Seahorse (Hippocampus haema) in Geoje-Hansan Bay, Korea

ABSTRACT Kim, M.J.; Kim, H.C.; Lee, W.C.; Park, J.M.; Kwak, S.N.; Oh, Y.; Kang, M.G., and Lee, S.H., 2018. Ecological characteristics of the new recorded seahorse in Geoje-Hansan Bay, Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 351–355. Coconut Creek (Florida), ISSN 0749-0208. A basic ecological research of the seahorse populations has not been done to date even though the population is declining due to overfishing, by-catching and heavy human activities. Recently reported seahorse (Hippocampus haema) samples were monthly collected in Geoje–Hansan bay for a year from August 2015 to August 2016. Standard length (SL), weight (Wt), coronet height (CH), trunk length (TrL), and tail length (TaL) of each individual were measured for identifying characteristics of H. haema. The ranges of temperature and salinity were 8.2–26.0 °C and 29.3–34.1 ‰, respectively. Mean SL and Wt for all the groups were 55.26 ± 16.11 mm and 0.32 ± 0.25 g, respectively. There were significant differences in the relative ratios of each length factor (TrL, TaL and CH) and condition factors (CFs) according to gender or breeding period (ANOVA, p < 0.01). Since pregnant males constituted nearly 40 % (18 individuals) in May and juvenile seahorses were first observed in June, 2016, the recruitment of this species appears to begin in June. Based on our one-year field observation, the duration of the breeding season of the H. haema in Geoje-Hansan bay can be estimated for approximately 7 months long which is similar to other seahorse species (generally 4 to 10 months) inhabiting similar latitudes. The results from this study provide important information for a sustainable management and conservation of the new recorded seahorse species.

Influences of diel and tidal cycles on fish assemblage in eelgrass (Zostera marina) bed of southern Korea during autumn

Short-term tidal and diel variations of autumn fish assemblage in a Zostera marina bed were investigated using 3 h interval samplings for 24 h in both spring and neap tide using a small beam trawl. A total of 1 346 fishes belonging to 19 species were collected at spring tide, whereas 1 115 fishes belonging to 17 species were at neap tide. The common fish species were Nuchequula nuchalis, Acanthogobius flavimanus, Takifugu niphobles, Acentrogobius pflaumii, and Pholis nebulosa with the former three species dominating at spring tide, while the latter two species being abundant at neap tide. Diel variation in abundance was significant with higher abundance at night than day, but there were no significant differences between spring and neap tides, and between ebb and flood tides (three-way ANOVAs). Diel variation in the abundance of fishes may be influenced by tidal range and cycle, and day-night differences of food availability and behaviors of fishes indirectly. Non-metric multidimensional scaling (nMDS) ordination and analysis of similarity (ANOSIM) results revealed significant differences in species compositions both between day and night, and between spring and neap tide. Eelgrass beds are highly productive marine ecosystem, and thus, our results will contribute to conservation of seagrass ecosystem in the study area.