First report on occurrence and distributions of Typhlocarcinops decrescens Rathbun, 1914 and Quadrella reticulata Alcock, 1898, through long-term ecological surveys of the Korea Marine & Costal National Park in 2015–2020

Brachyuran crabs are important benthic invertebrates which occur in diverse habitats along Korean coastal waters, such as estuaries, tidal flats, and sandy shores. Recent six-years monitoring surveys along the Korea Marine & Coastal National Park provide new records of Typhlocarcinops descrescens Rathbun, 1914 and Quadrella reticulata Alcock 1898. Here, we described morphologies and distributions of both species in the Korean Peninsula. Typhlocarcinops descrescens occurred at 17 of 47 stations (Survey-I; 2015–2020) and 6 stations (additional collection), and generally inhabited seas of muddy substrates along the coasts. Quadrella reticulata was only detected at one station in Jeju among 32 islands (Survey-II; 2015–2019), indicating its recent introduction into Korean waters. The host species for Q. reticulata were four antipatharians found at a water depth of 25 m on Jeju Island. Interestingly, these four typical host species occurred at five stations in the southern sea of the Korean Peninsula during the five-year of Survey-II, but Q. reticulata was not recorded. At present, we propose the northern limit of the antipatharian-associated Q. reticulata is Jeju Island, showing its potential to disperse further north.