Anthropogenic decline of the peculiar fauna of estuarine mudflats in Japan

Abstract

Mudflats are formed in the upper littoral zones in estuaries, especially in the innermost part of macro-tidal embayments (upper reaches of estuaries), providing a habitat for peculiar fauna and flora. The peculiar fauna and flora of estuarine mudflats appear to have been extirpated in many estuaries in Japan, along with the mudflats that have been damaged or destroyed by thoughtless and drastic coastal reclamation. At present, Ariake Bay, which constitutes the largest area of mudflats remaining in Japan, also has the greatest variety of species. The mudflat-specific species are almost or completely restricted to Ariake Bay, while populations of the same (or closely related) species are distributed along Asian continental coasts, which suggests they are continental relicts. Some of the mudflat-specific species now restricted to Ariake Bay (e.g.,the bivalve, Tegillarca granosa, the polychaete, Hediste japonica, the salt marsh plant, Suaeda japonica) previously enjoyed a wide distribution in Japan. Even within Ariake Bay, huge mudflats in Isahaya Bay were recently lost to a reclamation project there. The high productivity of benthic organisms in mudflats seems to benefit carnivores such as birds and fishes (e.g., Japanese eel). Conservation and restoration of mudflats are needed to conserve endangered species and to maintain traditional human fisheries and culture. From this aspect, restoration of the largest mudflats in Isahaya Bay in Ariake Bay is highly desirable.

Fishing bait worm supplies in Japan in relation to their physiological traits

“…However, large parts of the sandy and muddy intertidal flats of the Japanese coast, including areas used by bait collectors, have disappeared because of anthropogenic coastal developments (e.g., reclamation, seawall construction) (Sato, 2010). To satisfy the demand of Japanese anglers, two species of nereid and eunicid worm have been imported from Korea since 1969, although the main source country shifted to China after the 1990s with an annual supply of approximately 1000 t and an increasing number of bait species (Hayashi, 2001).…”

Molecular evidence for the existence of five cryptic species within the Japanese species of <i>Marphysa</i> (Annelida: Eunicidae) known as “Iwa-mushi”

“…The distribution of Marphysa sp. B suggests that it may be a potentially relict species that was isolated from the original Asian continental coast population by geohistorical events and has existed only in the Ariake Sea, a semi-closed shallow sea with a large tidal flat and macro-tidal environment similar to the Bohai and Yellow Sea (Sato & Takita 2000, Sato 2010, 2017.…”

Differences in conservation candidate tidal rivers by cross‐taxon analysis in the Japanese temperate zone

“…Japanese coastal areas have some of the richest biodiversity in the world (Fujikura, Lindsay, Kitazato, Nishida, & Shirayama, 2010); however, more than 40% of its estuarine environments have been lost since the 1940s (Sato, 2010). One reason for this decline is the anthropogenic impact, caused by levee revetments, barrages, waterways, saline barriers, training levees, and the coastal protection work carried out against coastal erosion and tidal waves in the middle and lower stream regions of Japanese rivers from the 1950s (Takahasi & Uitto, 2004).…”