Distribution and Molecular Phylogeny of the Toxic Benthic Dinoflagellate Ostreopsis sp. in the Coastal Waters off Jeju Island, Korea

춘계 제주 연안에서 유독 저서성 와편모류 Ostreopsis sp.의 분포와 분자계통학적 위치

Abstract

We investigated occurrence and molecular phylogeny of the toxic epiphytic dinoflagellate Ostreopsis at seven sampling sites in the coastal waters off Jeju Island of Korea in April, 2017. During the sampling period, surface water temperature ranged from 15.7 to $18.3^{\circ}C$ and salinity was relatively constant, ranging from 33.4 to 34.9. Of a total of 13 macroalgal species collected from all sampling sites, Ostreopsis cells were observed from 8 macroalgal species and the highest cell abundance ($157.5cells\;g^{-1}$) was recorded on the red alga Grateloupia filicina at St. 6. LSU rDNA D8/D10 sequences of all Korean Ostreopsis strains isolated from the 4 sampling sites were 100% identical. Molecular phylogentic analyses (BI and ML) inferred from LSU rDNA alignment showed that the Korean Ostreopsis strains placed into the previously described the Ostreopsis sp. 1 clade, which contained strains isolated from the temperate coastal waters of Japan. The Korean Ostreopsis sp. 1 strain grew in a wide range of temperature ($10-30^{\circ}C$) and salinity (25-30), with its maximum growth rate of $0.49d^{-1}$ at $25^{\circ}C$ and salinity of 30, indicating that they can be tolerated in temperate areas.

본 연구는 2017년 4월 춘계 제주 연안에서 총 7개의 정점(협재, 이호테우, 함덕, 성산, 표선, 남원, 사계)을 선정하여 해조류에 부착하여 서식하는 유독 착생 와편모류 Ostreopsis의 출현양상을 조사하고 분자계통학적 분석을 실시하였다. 본 연구 해역의 표층 수온은 $15.7^{\circ}C-18.3^{\circ}C$의 범위를 보였으며, 염분은 33.4-34.9의 범위로 나타났다. 각 연구 정점에서 채집된 전체 13종의 해조류 가운데 8종에서 Ostreopsis가 출현하였으며, 정점 6에서 출현한 홍조식물 참지누아리(Grateloupia filicina)에서 해조류 단위 무게당 Ostreopsis의 출현밀도($cells\;g^{-1}$)가 $157.5cells\;g^{-1}$로 가장 높은 농도로 출현하였다. Ostreopsis가 출현한 4개의 연구정점에서 분리한 종주들의 LSU rDNA D8/D10 영역의 염기서열은 모두 100% 동일한 것으로 나타났다. LSU rDNA 염기서열 정보를 이용한 분자계통수에서 이들은 모두 Ostreopsis cf. ovata의 잠재종(cryptic species)으로 알려진 Ostreopsis sp. 1의 분기군에 속하는 것으로 나타났다. Ostreopsis sp.1 종주를 이용하여 수온과 염분에 따른 생장 반응을 측정한 결과, $10-30^{\circ}C$의 광범위한 수온과 20-35의 염분 범위에서 뚜렷한 생장을 나타내었고, 수온 $25^{\circ}C$와 염분 30에서 $0.49d^{-1}$의 최고 생장률을 나타내었다. 또한, 수온 $10^{\circ}C$의 저온에서도 염분 35에서 뚜렷한 생장을 보여, 이들은 온대 해역에서 적응하여 정착한 종으로 판단된다.

Fig. 1. A map showing sampling locations off Jeju Island of Korea.

Fig. 2. Cell abundances (cells g-1) of the epiphytic dinoflagellate Ostreopsis spp. at each sampling site. Error bars represent standard error of mean.

Fig. 3. Bayesian phylogeny of Ostreopsis species inferred from 28S rRNA gene (D8/D10 regions). Med/Pac, SCS, and Thailand are the O. cf. ovata subclades collected from Mediterranean Sea and Pacific Oceans, South China Sea, and Thailand, respectively. Ostreopsis sequences collected from Jeju Island are represented in bold. Bootstrap supports (>50%) from maximum likelihood and Bayesian posterior probabilities (>0.60) are shown at nodes.

Fig. 4. Light micrographs of Ostreopsis sp. (A) Living cell, (B) Epithecal view, (C) Hypothecal view. Scale bars=20μm.

Fig. 5. Growth curves of Ostreopsis sp.1 (HJ1-4) with functions of temperature and salinity.

Fig. 6. Contours of the growth rates of Ostreopsis sp. 1(HJ1-4) as functions of temperature and salinity.

Table 1. Location, water temperature, and salinity at each sampling site during this study

Table 2. Cell abundance of the benthic dinoflagellate Ostreopsis spp. on macroalgae collected from each sampling site along the coasts off Jeju Island, Korea during April 2017

Table 3. Comparison of morphometric features between Ostreopsis sp.1 and O. cf. ovata subclades determined by light microscopy. Values represent as ranges (mean ± standard deviation). DV, dorso-ventral diameter; W, trans-diameter

Table 4. Summary of a two-way ANOVA test for growth rates of Ostreopsis sp. 1(HP1-4) as a function of temperature and salinity