INTRODUCTION
Ulmaridae is one of the three traditional jellyfish families included in the order Semaeostomeae, class Scyphozoa. Species within Ulmaridae differ from the other species within the other two families (Pelagiidae and Cyaneidae) by their branched radial canals and their circular canal (Mayer, 1910). About one-third of the 40 species (14 genera) in Ulmaridae belongs to the genus Aurelia, and the rest of them are mostly deep-water species (Daly et al., 2007).
Up to date, only six scyphomedusae species have been reported from Korean waters (Park, 2000, 2002; Park and Chang, 2006; Ullah et al., 2015), most of which are temperate and subtropical species. Although some deep- and coldwater jellyfish species were found in Japanese waters (Miyake et al., 2002, 2005), none have been recorded in Korean waters yet. This might be due to most cold-water species being distributed in deep-water, which is difficult to survey.
In the present study, cold-water jellyfishes were sampled from Korean waters using set nets (fixed shore net, fish trap, and bottom trawl net). Based on examinations of their morphology and DNA comparisons, individuals were identified as Aurelia limbata Brandt, 1835 and Parumbrosa polylobata Kishinouye, 1910, both belonging to Ulmaridae (order Semaeostomeae).
This study aimed to provide morphological descriptions of two cold-water jellyfishes first reported from Korean waters. Moreover, genetic information based on nuclear ribosomal DNA (rDNA) was used to support identification of both species and establish their phylogenetic relationships with other medusae.
MATERIALS AND METHODS
Study sites and sample collection
Thirty-four individuals of Scyphomedusae were collected from the coasts of Gangneung (37°47′44.06″N, 128°57′7.32″ E), Ulsan (35°36′21.07″N, 129°28′37.73″E), and Boryeong (36°17′53.81″N, 126°28′33.94″E), and from the center and the eastern Yellow Sea (34°15′00.00″N, 123°15′00.00″E-37°19′50.00″N, 126°28′67.00″E) in Korean waters using fixed shore nets, fish traps, and bottom trawls, from June, 2006 to May, 2015 (Fig. 1). The water temperature and depth at which scyphomedusae were sampled were recorded by a Sea-Bird conductivity-temperature-depth (CTD) instrument (SBE-911; Sea-Bird Electronics Inc., Bellevue, WA, USA). Whole specimens (n=34) were preserved in 5% (v/v) formalin (Junsei, Tokyo, Japan) whereas umbrella tissue samples (n=6) were preserved in 99.9% ethanol (Merck, Darmstadt, Germany) for their further use in nuclear DNA analyses.
Fig. 1.Aurelia limbata and Parumbrosa polylobata sampling sites in Korean waters.
Morphological analysis and description
The width and height of umbrellas were measured from each specimen. Using a stereomicroscope (Leica MZ 12; Leica Microsystems, Wetzlar, Germany), the umbrella, marginal lobes, rhopalium, marginal tentacles, mouth, stomach, gastric pouch, manubrium, subgenital cavity, and canal system of the sampled jellyfish were morphologically analyzed and photographed using a digital camera (Cannon G10; Cannon, Tokyo, Japan). The morphology of the individuals identified as A. limbata was compared to those previously published for this species (Brandt, 1835; Kishinouye, 1910; Uchida, 1954; Kramp, 1961; Yamaji, 1984; Larson, 1990; Miyake et al., 2002) and for Aurelia labiata (Mayer, 1910; Gershwin, 2001). Similarly, records obtained for the individuals identified as Parumbrosa polylobata were compared to those previously published in Kishinouye (1910), Mayer (1910), Uchida (1954), Kramp (1961), Yamaji (1984), and Miyake et al. (2005).
Molecular analysis and species identification
Genomic DNA (gDNA) was extracted from the umbrella of four A. limbata and two P. polylobata specimens. Before extraction, alcohol-preserved tissues were washed in distilled water to remove all ethanol and to avoid contamination from the zooplankton contained in the stomach of jellyfish. Total gDNA was extracted by using the method described by Asahida et al. (1996). Nuclear rDNA sequences spanning the internal transcribed spacer 1 (ITS1), partial sequence, 5.8S ribosomal RNA gene, complete sequence, internal transcribed spacer 2 (ITS2), complete sequence and 28S ribosomal RNA gene, partial sequence were amplified using the forward primer jfITS-5f (5′-GGTTTCCGTAGGTGAACCTGCGGAAGGATC-3′) and the reverse primer 28S-2R (5′-GCTTTGGGCTGCAGTCCCAAGCAACCCACTC-3′) (Dawson, 2004). Amplified PCR fragments were purified and sequenced on an automated sequencer (ABI 3730Xl; Applied Biosystems, Foster City, CA, USA). The four sequences obtained for A. limbata and the two sequences obtained for P. polylobata were compared with nuclear rDNA regions retrieved from the National Center for Biotechnology Information (NCBI) database (http://www.ncbi.nlm.nih.gov). Sequences of A. limbata from Hokkaido, Japan (Genbank accession No. AY 935215.1), A. limbata from Alaska, USA (AY935211.1), A. aurita from Rhode Island, USA (AY935205.1), Aurelia sp. 1 from Miyazu Bay, Japan (AY935214.1), Aurelia sp. 3 (AY935209.1), Aurelia sp. 4 (AY935208.1), Aurelia sp. 5 (AY935210.1), Aurelia sp. 6 (AY935207.1), Aurelia sp. 7 (AY935212.1), Aurelia sp. 8 (AY935217.1), and A. labiata from Alaska, USA (AY935202.1), all deposited by Dawson et al. (2005), Aurelia sp. 1 from Busan, Korea (EU332744.1) (Ki et al., 2008) and Cyanea capillata (U65481.1) (Odorico and Miller, 1997) were used as reference sequences for the class Scyphozoa, Craspedacusta sowerbyi Lankester, 1880 (FJ423631.1) was used as a reference sequence for the class Hydrozoa, and Parazoanthus axinellae (EU363364.2) (Reimer et al., 2008), a member of the class Anthozoa, was used as outgroup.
The 22 sequences were aligned using Clustal X (Larkin et al., 2007) and their genetic distances were calculated in MEGA 6 (Tamura et al., 2013). Analyses were conducted using the Kimura 2-parameter model. There were a total of 730 positions in the final dataset. Maximum likelihood (ML) phylogenetic trees were reconstructed using a heuristic search and the general time reversible model (GTR), as included in MEGA 6. Branch support in the ML trees was obtained by bootstrap analysis using 1,000 replicates.
SYSTEMATIC ACCOUNTS
1*Aurelia limbata Brandt, 1835 (Fig. 2A-E)
Fig. 2.Aurelia limbata Brandt, 1835. A, Whole body in side view; B, Aboral view; C, Radial canal system; D, Expanded oral arms; E, Diagram showing all structures observed in oral view. ac, adradial canal; g, gonad; ic, interradial canal; m, umbrella margin; mt, marginal tentacles; o, oral cavity; oa, oral arm; pc, perradial canal; rh, rhopalium; sc, stomach cavity. Scale bars: A=5 cm, B-E=3 cm.
Material examined. Korea: 5 individuals, Gangwon-do: off Gangneung (37°47′44.06″N, 128°57′07.32″E), 31 Aug 2007, Chang SJ; 7 individuals: off Ulsan (35°36′21.07″N, 129°28′ 37.73″E), 9 Jun 2011, Chang SJ.
Morphological description. Umbrella hemispherical when contracted but flat when expanded, about 250-500 mm in width and 30-50 mm in height. Exumbrella water-white and subumbrella dark brown in color. Gelatinous substance (mesoglea) thick at center and thin toward margin. Umbrella margin divided into 16 marginal lobes with 16 shallow notches at regular intervals, 8 rhopalia located between clefts of lappets. Numerous thin and long tentacles, dark yellow or brown, rising from umbrella margin.
Single and simple mouth situated at center of subumbrella. Manubrium cruciform from top view but triangular in lateral view. Four frilly oral arms extended from manubrium to umbrella margin, nematocyst warts scattered on abaxial side of oral arms. Stomach divided into 4 gastric pouches with subgenital cavity and subgenital pore. Subgenital cavity enclosed with dark brown gonads.
Vascular system complex and branches anastomosed. Sixteen radial canals extend to the circular canal around umbrella margin. Four interradial canals begin from gonads, 4 perradial canals begin from mouth and 8 adradial canals begin from central part of gonads. Each adradial canal reaches circular canal without any confluence. Perradial canals and interradial canals branched around gonad part but anastomosed at umbrella margin. Vascular system clear in 250 mm width medusa whereas complex in 500 mm width medusa due to canals’ confluence.
Distribution. Pacific Ocean: Korea (East Sea), Japan (Hokkaido); Okhotsk Sea; Alaska; Bering Sea; Cold waters.
Remarks. Umbrella of A. limbata (250-500 mm in width) reported here is larger than that of A. aurita (40-110 mm in width) reported by Park (2000). Aurelia aurita have an eightscalloped umbrella margin whereas A. labiata and A. limbata have a 16-scalloped umbrella margin. Aurelia labiata and A. limbata differ on the color of the umbrella (milky white vs. chocolate brown), on the shape of the manubrium (rounded vs. pyramidal) and on the secondary scalloping of the umbrella margin (present in A. labiata and absent in A. limbata) (Gershwin, 2001).
Aurelia limbata were found between 6.6-9.9℃ and 30- 50 m depth in the coastal areas of Gangneung and Ulsan in the East Sea. Larval decapods are the basic prey of A. limbata (Zavolokin et al., 2008).
In this study, DNA sequences of A. limbata of the region spanning ITS1 (partial sequence), 5.8S, ITS2, and 28S (partial sequence) rDNA were deposited in GenBank (accession Nos. KX943298 to KX943301).
1*Parumbrosa polylobata Kishinouye, 1910 (Fig. 3A-C)
Fig. 3.Parumbrosa polylobata Kishinouye, 1910. A, Whole body; B, Margin of umbrella; C, Diagram showing all structures observed in oral view. g, gonad; ic, interradial canal; mt, marginal tentacles; o, oral cavity; oa, oral arm; pc, perradial canal; rh, rhopalium; sc, stomach cavity. Scale bars: A–C=2 cm.
Material examined. Korea: 5 individuals, Chungcheongnamdo: off Boryeong (36°17′53.81″N, 126°28′33.94″E), 25 Apr 2006, Chang SJ; 4 individuals, Korea-China Provisional zone in the Yellow Sea (34°15′00″N, 123°15′00″E; 34°45′ 00″N, 123°15′00″E; 36°15′00″N, 123°45′00″E), 28-30 Jul 2007, Chang SJ; 13 individuals, the Eastern part of the Yellow Sea (34°15′00.00″N, 123°15′00.00″E-37°19′50.00″N, 126°28′67.00″E), 1-6 May 2015, Kim JN, Kim JE.
Morphological description. Umbrella flat and disc-shaped, 80-200 mm in width and 20-40 mm in height. Gelatinous umbrella colorless, transparent; small granulated spots scattered over exumbrella. Very weak muscle system in subumbrella. Umbrella margin divided into octants, each comprising 1 divergent ocular lobe, 3 tentacles, and 8 velar lobes (64 in total). Cores of tentacles and lobes opaque white with their transparent margins.
One single and simple mouth at center of subumbrella. Stomach cavity round and flat with four interradial cavities connected by subgenital cavities. Four oral arms bifurcated, spear-head shape, and nearly as long as umbrella diameter.
Gonads opaque, white-pink, and lotus shaped. Gonads enclosed around stomach cavity and reflected through transparent exumbrella. In interradial cavity, gonads triangularly layered in transvers section and mixed with numerous long gastric cirri.
Simple vascular system extended to circular canal around umbrella margin. Four interradial canals, 8 adradial canals, and 4 perradial canals. Adradial canals located between interradial and perradial canals, reaching circular canal in a straight line. Interradial canal split from gonads to the umbrella margin.
Distribution. Pacific Ocean: Korea (Yellow Sea), Japan (Japanese coast of East Sea, Suruga Bay); cold waters.
Remarks. Parumbrosa polylobata were found at 6.4-10.0℃ and 40-90 m depth in Korean waters. Euphausia pacifica were found in the stomach cavity of P. polylobata. DNA sequences of P. polylobata of the region spanning ITS1 (partial sequence), 5.8S, ITS2, and 28S (partial sequence) rDNA were deposited in GenBank (accession No. KX943302).
DISCUSSION
Mayer (1910) defined three species (A. aurita, A. labiata, and A. solida Browne, 1905) and 13 varieties within the genus Aurelia. However, most scientists used Kramp’s (1961) classification concerning two species (the circum global A. aurita and the arctic A. limbata) until the end of the 1990s (Larson, 1990; Arai, 1997). With the development of electronic journals and photo sharing, three morphological species of A. aurita, A. limbata and A. labiata were distinguished (Gershwin, 2001) Moreover, with the development of molecular tools, at least 13 Aurelia species (Aurelia sp. 1-10) including A. aurita, A. labiata, and A. limbata were distinguished based on nuclear rDNA and mitochondrial cytochrome oxidase I (Dawson and Jacobs, 2001; Dawson et al., 2005) and on ITS1 (Schroth et al., 2002; Dawson, 2003) sequence data. Based on morphological data, Park (2000) reported A. aurita in Korean waters and these specimens were molecularly assigned as Aurelia sp. 1 by Ki et al. (2008).
The present study, the analysis of pairwise genetic distances from ITS1 to 28S rDNA among genus Aurelia (Table 1), revealed that sequences of the A. limbata specimens collected in Gangneung were 99.5% identical to that of A. limbata collected in Hokkaido (AY935215.1) and 92.9% similar to that of A. limbata from Alaska (AY935211.1). In addition, the rDNA region examined differed about 11.1% to 11.6% between Korean A. limbata and Korean Aurelia sp. 1 (AY935244.1), about 16.8% to 17.0% between Korean A. limbata and A. aurita (AY935205.1), and about 17.2% to 17.5% between Korean A. limbata and A. labiata (AY93502. 1). Thus, these results seem to contradict the hypothesis that A. limbata is a color morph of A. labiata (Gershwin, 2001).
Table 1.A_limbata, Aurelia limbata; A_aurita, Aurelia aurita; A_labiata, Aurelia labiata; Gn, Gangneung, Korea; JH, Japan, Hokkaido; Al, Alaska, USA; Rd, Rhode Island, USA; Bs, Busan, Korea; JM, Japan, Miyazu Bay.
In this study, A. limbata, A. aurita, A. labiata, and Aurelia sp. 1 are monophyletic according to the ML tree reconstructed based on their ITS1 to 28S DNA sequences. ML phylogenetic tree constructed with Semaeostomeae members, including A. limbata, Aurelia sp. 1, A. aurita, A. labiata, and P. polylobata showed that identical species were clustered together, but different species were clearly seperated, which were supported by high bootstrap values (Fig. 4).
Fig. 4.Phylogenetic maximum likelihood (ML) tree constructed for Aurelia limbata, Parumbrosa polylobata, and the other species (class Scyphozoa, class Hydrozoa, and class Anthozoa), based on ITS1 to 28S nuclear DNA sequences, using a general time reversible model of evolution. Numerals above the branches refer to the percentage of the 1,000 bootstrap replications supporting each node. Bootstrap indices under ML are shown at each node. A aurita, Aurelia aurita; A labiata, Aurelia labiata; A limbata, Aurelia limbata; Cr sowerbyi, Craspedacusta sowerbyi; Cy capillata, Cyanea capillata; Pa axinellae, Parazoanthus axinellae; P polylobata, Parumbrosa polylobata; Gn, Gangneung, Korea; JH, Japan, Hokkaido; Al, Alaska, USA; Bs, Busan, Korea; JM, Japan, Miyazu Bay; Rd, Rhode Island, USA; YS, Yellow Sea.
Aurelia limbata is distributed in the East Sea (this study), Alaskan waters (Larson, 1990), Tohoku region to Hokkaido, the Okhotsk Sea, the Bering Sea (Kishinouye, 1910; Uchida, 1954; Kramp, 1961; Larson, 1990; Wrobel and Mills, 1998; Zavolokin et al., 2008; Zavolokin, 2010, 2011), and the northern part of the Japanese waters (Pogodin, 1998; Miyake et al., 2002; Zavolokin, 2010). Individuals were found in the epipelagic and mesopelagic zone of the sea of Okhotsk and Bering Sea (Zavolokin et al., 2008; Zavolokin, 2010, 2011) and at about 2.0℃ and 33.4 psu from 200 to 250 m depth in Hokkaido, northern Japan (Miyake et al., 2002). Moreover, A. limbata were found at about 6.6-9.9℃ and 30-50 m depth in Gangneung and Ulsan in this study. These coastal areas of the East Sea are influenced by the Korean Strait Bottom Cold Water (KSBCW), which is a less saline water mass below 10℃ (Na et al., 2010) known to originate from the North Korean Cold Water (NKCW), a coastal mode of the East Sea Intermediate Water (ESIW) (Cho and Kim, 1998). Therefore, the cold-water masses from ESIW to KSBCW might restrict with the distribution of A. limbata in the East Sea.
In addition, Parumbrosa polylobata were recorded from Toyama Bay deep waters (>130 m depth) in 1907 (Kishinouye, 1910). Individuals observed at 267-509 m depth off the Pacific coast of Japan (Miyake et al., 2005) were found at 6.6-9.2℃ and 34.2-34.4 psu. In the present study, P. polylobata were found at about 6.4-10.0℃ and 40-90 m depth in the center of the Yellow Sea. This species fed on several gelatinous zooplankton such as Salpa fusiformis, Siphonophora, and Solmissus sp. (Miyake et al., 2005), and on Euphausia sp. in this study. During winter, P. polylobata is distributed from the western coast of Korean waters to the center of the Yellow Sea whereas during summer it is distributed in the center of the Yellow Sea, where the Yellow Sea Cold Bottom Water (YSCBW) remains. Thus, the YSCBW seems to affect the distribution of P. polylobata.
This study is the first step to report cold-water jellyfishes from Korean waters. Moreover, records of genetic information of nuclear rDNA from two cold-water jellyfishes will be a useful identification key to discriminate species. In future, monitoring these two cold-water species might be important to evaluate climate changes in the East Sea and in the Yellow Sea.
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