Taxonomic Notes
The Korean Seahorse (Hippocampus haema) has commonly been confused with the High-crowned Seahorse (H. coronatus Temminck and Schlegel 1850) and the Sindo’s Seahorse (H. sindonis Jordan and Snyder 1901). However, Han et al. (2017) have described it as a distinct species based on morphological and molecular analyses.
Justification
The Korean Seahorse occurs in the Northwest Pacific from Soan Island to Ulleungdo Island in Korea and from Kagoshima Prefecture to Akita Prefecture in Japan. This seahorse inhabits areas dominated by Common Eelgrass (Zostera marina) and Sargassum seaweed beds at depths of 0–18 m. Common Eelgrass meadows are threatened by sea filling, eutrophication, aquaculture, fisheries, and climate change, and it is inferred that there has been an ongoing decline in Common Eelgrass cover within this seahorse’s range. Incidental catch in seine nets is a minor threat. Given the continuing declines in Common Eelgrass cover, it is suspected that there has been a reduction of 30–50% in this seahorse’s population. The Korean Seahorse is therefore assessed as Vulnerable A2c. Further research is needed on its population and habitat trends.
Geographic Range Information
The Korean Seahorse occurs in the Northwest Pacific. In Korea, it is found along the southern and southeastern coasts from Soan Island to Pohang, North Gyeongsang, and in Ulleungdo Island to the east of the Korean Peninsula (Han et al. 2017, GBIF 2023). In Japan, it is found along the western and northwestern coasts from Kagoshima Prefecture to Akita Prefecture (Han et al. 2017).
This seahorse was collected by Aizawa and Ikeda (2023) from the Koyadori Fishing Port in Miyagi Prefecture, Japan. However, given that only one individual was collected during the survey period (May–December 2022), the individual is thought to have been carried by ocean currents along with drifting seaweeds from Korea but did not become established in the region (Aizawa and Ikeda 2023).
Population Information
There is no range-wide population estimate for this seahorse. However, there are some local surveys and population data for this seahorse, mostly from Korea (Han et al. 2017).
Choi et al. (2012) found 555 individuals between 2003 and 2005 in Gamak Bay, Yeosu, with density ranging between 0–6.5 individuals/1,000 m² and a mean density of 2.9±0.6 individuals/1,000 m². Jung et al. (2007) found two individuals from the bay in 2004 and a density of 0.96 individuals/m². Kim et al. (2016) found 45 individuals from the shores near Yeosu in 2014, with a density of 2.7–61.2 individuals/1,000 m².
From other studies in Korea, 913 individuals were found in Geoje-Hansan Bay between 2015 and 2016 (Kim et al. 2018), 293 individuals were found in Soan Island between 2015 and 2016 (Cho et al. 2022), 164 individuals were found in Dongdae Bay between 2006 and 2007 (Huh et al. 2014), and a density of 19.4 juveniles/1,000 m3 were found in Gwangyang Bay in 2014 (Chu et al. 2019).
Given the extensive, ongoing degradation and decline in Common Eelgrass, it is suspected that there has been a population reduction of 30–50% over the last 10 years for the Korean Seahorse.
Habitat and Ecology Information
The Korean Seahorse is typically found in shallow coastal areas at depths of 0–18 m (Han et al. 2017), although two individuals have been found at a depth of 30 m (Kim et al. 2016). It has been found in areas dominated by the Common Eelgrass (Zostera marina) (Choi et al. 2012, Cho et al. 2022) and seaweed (Sargassum piluliferum) (Kim et al. 2018, Kim et al. 2022).
It mainly feeds on small crustaceans such as amphipods, copepods, isopods, and mysids (Huh et al. 2014, Kim et al. 2022). Huh et al. (2014) found ontogenetic changes in its diet, where smaller individuals consumed copepods and larger individuals consumed gammarid amphipods and mysids. Kim et al. (2022) found that the amphipod Caprella sp. was dominant in this seahorse’s diet in the summer, while the isopod Ianiropsis sp. was dominant in the winter, which suggest that its diet can vary depending on the seasonal availability of prey.
The maximum recorded height for this seahorse is 10 cm (Wibowo et al. 2017). Half of males and females are estimated to reach maturity at heights of 6.49 cm and 6.1 cm, respectively (Park and Kwak 2015). Its breeding season is estimated to occur between May and November, which may correlate with the higher water temperature during this period (Park and Kwak 2015, Kim et al. 2018). Brooding occurs in the male brood pouch, with each pouch containing 20–76 eggs (Cho et al. 2022). The average length at birth is around 1.1 cm (Park and Kwak 2015).
Threats Information
The Korean Seahorse may be caught incidentally in seine nets (Choi et al. 2012), but it is primarily threatened by habitat loss and degradation.
In Japan, Common Eelgrass cover has declined since the 1960s mainly due to sea filling. It was estimated that Common Eelgrass beds have declined by more than 30% in Ariake Bay and Kagoshima Bay between 1978 and 1991 (Aioi and Nakaoka 2003). In the Seto Inland Sea, more than 70% of Common Eelgrass beds was estimated to have disappeared since 1977 due to pollution and trawling (Aioi and Nakaoka 2003).
In Korea, 50–80% of seagrass cover was estimated to have been lost since the 1970s due to sea filling, eutrophication, pollution (industrial pollutants), aquaculture (oyster and seaweed farms), fisheries (trawling, clamming), and boat traffic (Lee and Lee 2003, Lee et al. 2018). In the Nakdong River Estuary, a large area of Common Eelgrass meadows had disappeared due to sea filling projects in the 1980s, although partial recovery has been observed in the estuary (Park et al. 2009).
There is no indication of sea-filling slowing down in Japan or Korea, and thus the threat and subsequent habitat loss and degradation are ongoing.
Algal blooms are becoming more frequent along the Korean coasts (Lee et al. 2018). Common Eelgrass beds in Jindong Bay nearly disappeared due to a reduction in light availability and suffocation from the thick layer of mucus secreted by the algae (Lee et al. 2007).
Seagrass beds are also negatively affected by climate change. Kim et al. (2020) found a significant decrease in shoot density, biomass, and productivity of the Common Eelgrass with sudden increases in water temperature, while Qin et al. (2020) found reduced sexual reproduction of Common Eelgrass under high water temperatures. Climate change can also increase the frequency and intensity of typhoons, which have caused die-offs in Common Eelgrass beds in Jangheung Bay, Korea (Kim et al. 2015, Lee et al. 2018).
Given the ongoing pressure on seagrasses, it is inferred that there has been an ongoing decline in Common Eelgrass cover within the Korean Seahorse’s range.
Use and Trade Information
The Korean Seahorse has not been recorded in trade.
Seahorses in general are traded live for display in aquaria or dried for use in traditional medicine or as curios (Vincent et al. 2011). In Korea, the High-crowned Seahorse (Hippocampus coronatus)—potentially a misidentification of the Korean Seahorse—is known to have high medicinal value in traditional medicine and may be used as a material for cosmetics (Lee et al. 2011, 2012), or consumed as health food (Wei 2020).
The High-crowned Seahorse has been involved in live trade, with around 1,200 wild-sourced individuals being officially reported in the CITES trade database between 1997 and 2004 before the listing of all seahorses in CITES Appendix II (UNEP-WCMC 2022). However, this quantity only reflects seahorse imports into EU member states before the genus was listed on CITES (Foster et al. 2021).
After the CITES Appendix II listing in 2004, there were fewer trades of the High-crowned Seahorse officially reported in the CITES database. Two live trades involving 100 wild-sourced (source code W) and 15 captive-born (F1 generation; source code F) individuals were reported in 2005 and 2014, respectively, and one dried trade involving 52 seized specimens were reported in 2016 (UNEP-WCMC 2022). The dried trade volume may be an underestimate, given that most of the dried trade of seahorses is illegal and unreported (Foster et al. 2019), and the seahorse is potentially used as traditional medicine, cosmetics, or health food in Korea.
The Korean Seahorse may be involved in trade based on trades involving the similar-looking High-crowned Seahorse, but the level at which this seahorse is traded is unclear.
Conservation Actions Information
There are no species-specific management or conservation measures in place for the Korean Seahorse. However, all seahorses are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), meaning that seahorse exports are to be sustainable, legal, and monitored (Vincent et al. 2011).
This seahorse occurs in several marine protected areas in Korea and Japan, such as the Gamak Bay Marine Reserve and Wakasa Wan Quasi-National Park (UNEP-WCMC and IUCN 2023).
Further research is needed on its population size and trends, along with habitat trends. Regulating sea filling projects and monitoring habitat quality and trade are necessary for the continued persistence of this seahorse.
