Vol.:(0123456789) 1 3 Ocean Science Journal (2021) 56:99–105 https://doi.org/10.1007/s12601-021-00008-0 NOTE Genetic Structure and Diversity of the Moon Jellyfsh Aurelia coerulea Polyp Population in Jaran Bay, Korea, Revealed by Mitochondrial COI and 16S rRNA Genes Yoseph Seo 1  · Buhari Lawan Muhammad 1  · Jinho Chae 2  · Jang‑Seu Ki 1 Received: 25 August 2020 / Revised: 27 October 2020 / Accepted: 12 November 2020 / Published online: 19 April 2021 © Korea Institute of Ocean Science & Technology (KIOST) and the Korean Society of Oceanography (KSO) and Springer Nature B.V. 2021 Abstract Blooms of the moon jellyfsh (Aurelia coerulea) have been responsible for huge economic losses and environmental dis- ruptions in oceans around the world. The mass occurrence of these jellyfsh may be highly related to the benthic polyp populations; however, studies supporting this are scarce. Here, we analyzed the genetic diversity and structure of Korean A. coerulea, using two mitochondrial genes, COI and 16S rRNA, in 51 polyps collected from Jaran Bay (South Korea) that is greatly afected by the mass occurrence of the jellyfsh. Genetic diversity analysis identifed 20 and 9 haplotypes in COI and 16S rRNA genes, respectively. TCS network analysis and haplotype distance matrix revealed a signifcant genetic structure in both genes. In addition, two distinct haplogroups (A and B) coexisted in Jaran Bay, and a single haplotype (COI-H4 or 16S-H2) dominated. These fndings suggest a strong population diferentiation among the polyp population that may have an efect on the jellyfsh blooms in Jaran Bay. Keywords Moon jellyfsh · Aurelia coerulea · Mitochondrial gene · Population genetics 1 Introduction Jellyfsh outbreaks are considered a natural phenomenon (Hamner and Dawson 2009). However, their geographic expansion or mass occurrence may be due to the increase in seawater temperature and coastal eutrophication by sew- age discharges (Arai 2001; Mills 2001). Large aggregations (blooms) of certain jellyfsh have caused several negative socio-economic impacts in many harbors and coastal waters around the world. Jellyfsh blooms have caused damages to fsheries (Quiñones et al. 2013), and obstruct cooling intakes of power plants and ships (Abdul Azis et al. 2000; Ki et al. 2008). Blooms also cause problems for aquaculture (Purcell et al. 2013). These socio-economic problems related to jel- lyfsh have been reported in North California, San Francisco Bay (Greenberg et al. 1996), the Gulf of Mexico (Frolova and Miglietta 2020), and South Korea (Ki et al. 2008; Yoon et al. 2018). Jellyfshes, including Aurelia, have a metagenetic life cycle, including the foating adult medusa and the benthic larva polyp stages (Ramšak et al. 2012). Each medusa forms a planula through sexual reproduction, which attaches to the benthic surface and grows into a polyp. Through asexual reproduction, the polyp makes several genetically identical strobilae that can grow into numerous medusae each year. In addition, a polyp can produce podocysts that are dormant but which later can emerge as new polyps (Arai 2008). This potential asexual reproductive ability of polyps probably has a signifcant efect on the blooms of the medusae (Arai 2008; Schiariti et al. 2014). Hence, researchers have emphasized the importance of benthic polyp populations and their link to mass medusae occurrence (Arai 2008; Marques et al. 2019; Mills 2001; Purcell 2009). The moon jellies of the genus Aurelia are one of the widely distributed jellyfshes worldwide. Diferent species belonging to the genus Aurelia are very similar in form, making it hard to accurately distinguish the species mor- phologically. According to the WoRMS database (Collins et al. 2020), a total of ten Aurelia species, including three well-known species, A. aurita, A. limbata, and A. labiata, Online ISSN 2005-7172 Print ISSN 1738-5261 * Jang-Seu Ki kijs@smu.ac.kr 1 Department of Biotechnology, Sangmyung University, Seoul 03016, Republic of Korea 2 Marine Environmental Research and Information Laboratory, Gunpo 15850, Republic of Korea