The geographical distribution of the toxic blue-lined octopus (commonly known as the blue-ringed octopus),
Members of the octopus genus
[Fig. 1.] Geographical distribution of the blue-lined octopus observed in the East/Japan Sea and adjacent waters and the general pattern of surface currents in the sea and neighboring waters. Acute angled triangles indicate geographical distribution of the blue-lined octopus along the Pacific coast of Honshu Island, Japan (from Kubodera, 1994). The localities of circled numbers correspond to the place numbers in Table 1. TWC, Tsushima Warm Current; EKWC, East Korean Warm Current.
was distributed north to the southern islands of the Japanese coast until the 1970s (Hashimoto, 1977), but the distributional boundary of the species moved northward to the Boso Penin-sula (refer to Fig. 1) on the Pacific Coast of Honshu Island in the 1990s (Kubodera, 1994). Incidentally, a specimen of
Biotic and abiotic factors may influence the distribution of marine organisms (Kolar and Rahel, 1993; Bhattacharjee et al., 2009) and the distribution of cephalopods, including octo-puses, can be affected by environmental factors (Boyle, 1990; Semmens et al., 2004; Pierce et al., 2008; Leite et al., 2009). Water temperature has a fundamental effect on physiologi-cal processes and the maintenance of homeostasis in aquatic animals (Venables et al., 1978; Hoegh-Guldberg and Bruno, 2010), and it is probably one of the most important factors influencing the distribution of octopuses (Collins, 2002; Che-dia et al., 2010). Recent sea warming could cause a shift in the distribution of marine organisms from low-latitude regions toward the poles (Walther et al., 2002; Parmesan and Yohe, 2003; Perry et al., 2005). The East/Japan Sea is one of the most rapidly warming large marine ecosystems in the world (Belkin, 2009), and its warming is expected to cause migration of marine organisms from subtropical waters. Spread of the blue-lined octopus from adjacent subtropical water into the East/Japan Sea could be a significant threat to Koreans and Japanese because the organism possesses a powerful toxin. Furthermore, coastal residents along the East/Japan Sea have no experience with the dangers of this species of octopus. Esti-mating the geographical distribution of the blue-lined octopus would be useful for public safety. However, there are very few published reports on the geographical distribution of the blue-lined octopus in the East/Japan Sea, except for one specimen that was found on Oki Island, Japan (Kohtsuka, 2006).
Although direct survey techniques, such as visual surveys and fishing data, are more effective for estimating the spatial distribution of octopuses (Pierce and Guerra, 1994; Hill and Wilkinson, 2004; Leite et al., 2009), these methods require extensive field research and funding. We hypothesized that, because Internet use is widespread and there is common ac-cess to the Internet in Korea and Japan (International Tele-communication Union, 2010), information on websites may be used as basic data for a large-scale distribution survey of an organism.
In this study, we conducted a survey to determine the geo-graphical distribution of the blue-lined octopus using Internet search engines and a questionnaire. Individual observation records of the blue-lined octopus were gathered from web-sites in Korea and Japan, and every datum was used to create a large-scale geographical distribution map in the East/Japan Sea.
The East/Japan Sea is a semi-enclosed marginal sea sur-rounded by Korea, Japan, and Russia. It is connected to the ad-jacent ocean by shallow straits. Warm water originating from a branch of the Kuroshio Current, which is a strong warm cur-rent in the western North Pacific Ocean, flows into the East/Japan Sea through the Korea/Tsushima Strait and flows out through the other straits (Cho and Kim, 2000; Kim et al., 2001; Taegue et al., 2006; Na et al., 2009). The Northwest Pa-cific Ocean, especially the East/Japan Sea, the East China Sea, and the Kuroshio Current, are the most rapidly warming ma-rine environments in the world (Belkin, 2009). We designated the East/Japan Sea and adjacent waters as the survey area to determine changes in the distributional range of the blue-lined octopus in relation to climate change.
Four commercially available internet search engines were used to find records on the Internet. Daum ( http://www.daum.net/ ), Google Korea ( http://www.google.co.kr/ ), Naver (http://www.naver.com/), and Yahoo! Korea ( http://kr.yahoo.com/ ) were used for Korean information; goo (http://www.goo.ne.jp/), Google Japan ( http://www.google.co.jp/ ), MSN ( http://jp.msn.com/ ), and Yahoo! Japan ( http://www.yahoo.co.jp/ ) were used for Japanese information. The same search terms were entered in the search engines. Two words in the Korean language were entered at the same time in the Korean search engines because there is no common name for the blue-lined octopus (or the blue-ringed octopus) in Korea. One word (
Korean fishermen living on the southeast coast of Korea, such as Tongyeong and Geoje, and Ulleung Island located in the East/Japan Sea, were surveyed during July and August 2010. The questionnaire participants were 145 fishermen from Tongyeong, 53 fishermen from Geoje, and 42 fishermen from Ulleung Island. Before starting the survey, we explained, with photographs, the general characteristics of the blue-lined octo-pus including body size, change in body color and the brilliant iridescent blue lines or blue rings.
Internet reports of sightings of the blue-lined octopus around the East/Japan Sea are listed in Table 1; the locations were marked on a map and their geographical distribution is shown in Fig. 1. The circled numbers in Fig. 1 correspond to the place numbers in Table 1.
Overall, via the Internet, 32 sightings of the blue-lined octo-pus were found from 18 different regions in Korea and Japan. In Korea, there was some information on
In Japan, a total of 31 observation records of the blue-lined octopus were found on the Internet. Twenty-two cases were from the East/Japan Sea coast of Honshu Island, and nine cases were from the west coast of Kyushu Island (Table 2). The blue-lined octopus was first recorded along the Japanese coast of the East/Japan Sea in Maizuru Bay in 2004 (number 16 in Table 1 and Fig. 1). After this observation, the octopus was found in various regions on the East/Japan Sea side of Japan. The northern distributional boundary of the blue-lined octopus in the East/Japan Sea was off Sakai, Fukui Prefecture, Japan (around latitude 36°10' N). Based on information from four websites, the blue-lined octopus was observed 14 times on Omi Island (numbers 11 to 24 in the Appendix 1), Yama-guchi Prefecture, located on the southwest coast of Honshu, Japan (number 10 in Fig. 1). Although observed depths and water temperatures were not recorded in every case, the blue-lined octopus was found to a maximum depth of 19 m and in a water temperature range of 12-18℃. Furthermore, a blue-lined octopus, while brooding her eggs, was photographed four times on Omi Island from February to April 2009. These observations provide evidence of reproduction of the octopus in the East/Japan Sea. The blue-lined octopus was observed in all months of the year except September and October, but was found most frequently in April around the East/Japan Sea
(Table 2). We found that the blue-lined octopus was distribut-ed extensively around the East/Japan Sea side of Japan. To the best of our knowledge, this is the first report on the large-scale geographical distribution of the blue-lined octopus around the East/Japan Sea.
The Internet is a widespread source of information and its use is prevalent in Korea and Japan. In 2008, the percentage of households with access to the Internet in Korea and Japan was 94.3% and 79.8%, respectively (International Telecom-munication Union, 2010). Many observation records of the blue-lined octopus around the East/Japan Sea were gathered via the Internet. The Internet search method used here is not comparable to common systematic fisheries survey methods, such as fishing data or visual survey techniques (Pierce and Guerra, 1994; Hill and Wilkinson, 2004; Leite et al., 2009). A systematic survey of the blue-lined octopus over wide geo-graphical regions is not easy because of its small size and be-cause its skin color makes it almost invisible. Moreover, col-lection of accurate fishing data is difficult because there is no commercial fishery for the blue-lined octopus (Norman, 1998) and very little is known about its population density in specific areas. The results of our survey may not be sufficient as part of a public safety program, although they can provide useful information to warn of possible food poisoning or bites.
Through this study, we proved the usefulness of the Internet for a large-scale survey of the blue-lined octopus. In many cases, the date and place of observation or photos taken in the field of the blue-lined octopus were gathered. Species-specific features of the blue-lined octopus, such as iridescent blue lines on the dorsal mantle, can be observed in most of the octopus photos posted on the Internet. Country-specific commercial search engines were used in Korea and Japan. Some records were found by all search engines, while others were found only by some search engines. Several search engines were needed because different search engines provided different re-sults. Similar results have been reported by other investigators who have compared the usefulness of Internet search engines for finding health information (Wu and Li, 1999; Merion et al., 2000).
The blue-lined octopus is found along the Pacific Coast of Honshu Island and the southern islands of Japan (Kubodera, 1994), but very little is known about the geographical distribu-tion of the octopus on the East/Japan Sea coast of the country. Global warming is expected to cause migration of the blue-lined octopus from existing habitats, much the same as for fish (Walther et al., 2002; Parmesan and Yohe, 2003; Perry et al., 2005; Dulvy et al., 2008). Evidence of the spread of this octo-pus in the East/Japan Sea and adjacent waters was gathered in Korea and Japan. There was little evidence to suggest that this octopus occupies the Korean coast of the East/Japan Sea, con-trary to expectations. However, considerable evidence sup-porting the existence of blue-lined octopus in the East/Japan Sea was collected from Japan. In addition to the records listed in Table 1, more data that lacked objective evidence, such as an observation date or location, were excluded from the Japan data. The excluded data did not affect the northern distribu-tional boundary of the species because most of the incomplete data were obtained from regions south of southwestern Hon-shu Island, Japan.
We found four photos of a blue-lined octopus brooding eggs taken at Yamaguchi, Japan, on a website. This is obvi-ous evidence that the blue-lined octopus is reproducing in the southern East/Ja-pan Sea. We suggest that the southern East/Japan Sea has become a favorable reproductive environment for the blue-lined octopus. Brooding blue-lined octopuses were found at water temperatures between 13℃ and 16℃ (Table 1). Tranter and Augustine (1973) reported that the embryonic de-velopment time of the blue-lined octopus was about 2 months at seawater temperatures of 20.8-22.5℃. The embryonic de-velopmental period of
Although biotic and abiotic factors affect the distribution of octopuses in the natural environment (Mather, 1982; Boyle, 1990; Collins, 2002; Semmens et al., 2004; Pierce et al., 2008; Leite et al., 2009; Chedia et al., 2010), the geographical distri-bution of the blue-lined octopus in the southern part of Japan is strongly influenced by the Kuroshio Current (Kubodera, 1994). The East/Japan Sea is also influenced by the Tsushima Warm Current, which is a branch of the Kuroshio Current. The distribution of the blue-lined octopus around the East/Japan Sea most likely corresponds to the flow of the Tsushima Warm Current along the Japanese coast (Fig. 1). The Tsushima Warm Current flows into the East/Japan Sea through the Korea/Tsu-shima Strait and then separates into two or three branches. One branch, called the East Korean Warm Current, flows along the east coast of Korea and one branch flows along the Japanese coast, while the offshore branch is seasonally variable (Kaw-abe, 1982; Cho and Kim, 2000). Southeast regions, such as Tongyeong, Geoje, and Ulleung Island in Korea, are also in-fluenced by the Tsushima Warm Current, but no evidence of blue-lined octopus was collected from either Internet searches or questionnaires administered to local fishermen. Although the Tsushima Warm Current flows along the coasts of both Korea and Japan, there was a considerable difference in the distribution of the blue-lined octopus between the countries. We suggest that either the blue-lined octopus has received little attention in Korea or that there is another factor inter-rupting its settlement along the Korean coast.
The spread of the blue-lined octopus via water currents would be difficult because the octopus produces relative-ly large eggs and lacks a planktonic stage in its life history (Tranter and Augustine, 1973; Kubodera, 1994). Nevertheless, blue-lined octopus were found in large regions around the East/Japan Sea. This means that a part of the East/Japan Sea and adjacent waters may have changed to provide a suitable habitat for the blue-lined octopus, which originated in tropical and subtropical waters. The East/Japan Sea and the East China Sea around Korea and Japan are rapidly warming large marine ecosystems (Kim et al., 2001; Belkin, 2009). The net sea sur-face temperature increase in the East/Japan Sea and the East China Sea between 1982 and 2006 was 1.09℃ and 1.22℃, respectively (Belkin, 2009). The widespread distribution of the blue-lined octopus in the East/Japan Sea, originating from tropical or subtropical waters, is presumed to be caused by sea warming that occurred over a long period. Generally, pelagic species, especially fishes, are more sensitive to environmental change (including climate change) than benthos and demersal fish (Hiscock et al., 2004; Megrey et al., 2009; Rijnsdorp et al., 2009). Although the blue-lined octopus is a demersal spe-cies, the octopus was found at the relatively high northern lati-tude of 36°10' N. We suggest that sea warming has contributed to a slow northward shift in the distribution of the blue-lined octopus. Models predict that the surface water temperature in the East/Japan Sea will be 1-6℃ warmer in 2060 than at pres-ent (Murazaki et al., 2005). If the East/Japan Sea continues to warm, the blue-lined octopus will likely become more wide-spread, including along the Korean coast, especially along the southeast coast of the Korean Peninsula where it is signifi-cantly affected by the Tsushima Warm Current.
Recent sea warming is expected to cause migration of ma-rine organisms from adjacent subtropical waters to the East/Japan Sea. As we expected, the blue-lined octopus is widely distributed along the Japanese coast around the East/Japan Sea. Expansion of the range of the poisonous and venomous blue-lined octopus may increase human health risks. Invasion of the blue-lined octopus into the East/Japan Sea will increase concerns over health and food safety in Korea and Japan. Health and food safety authorities should educate the public on preventing food poisoning or envenomation by the blue-lined octopus.