Mudflats as ecosystem services hotspots
- Nakatsu, Oita, Japan

The importance of mudflats and their need for protection: a case study from Nakatsu mudflat, Japan

The term mudflat refers to the land near a water body that is regularly flooded by tides and is usually barren (without any vegetation). Also known as tidal flats, mudflats are formed by the deposition of mud carried by tides or rivers onto the shore. This coastal landform usually occurs in sheltered areas of the coast, like bays, coves, lagoons, estuaries, etc. Since are large proportion of mudflats are within the intertidal zone, they experience daily cycles of submersion under water and exposure to the air. They are important in helping to dissipate wave energy and so reduce the risk of eroding saltmarshes. This helps to prevent stress on coastal defenses and protect low-lying land from flooding. They also have an intrinsic natural beauty, adding to the unique landscape and seascape. Mudflats attract many migratory shorebirds. These intertidal areas also house several species of crabs, fish, and mollusks which form the food base for the migratory birds. Thus, mudflats are often significant bird-watching spots. However, mudflats across the world are in danger of destruction and under extreme threat from coastal developmental activities. Dredging for navigational needs, chemical pollution, etc., are threatening mudflat habitats. Also, climate change induced extreme weather conditions that trigger sea level rise are submerging substantial sections of mudflats. The loss of these tidal flats will make coastal areas vulnerable to the forces of erosion and floods. More than two thirds of the mudflats around the Yellow Sea have been destroyed over the past 50 years.

There are ten mudflats in Japan and Nakatsu mudflat, Oita Prefecture, is the second largest mudflat on Kyushu island. It has a long history of producing bountiful coastal resources (seaweeds, seagrass, fishes, crabs, etc.), which is reflected in the socio-economic activities and traditions of the area. It is reported that Nakatsu mudflat hosts 655 species of biota, out of which 229 are listed as endangered species in Japan. Because of the abundance of food resources, each year many migratory birds, like sandpipers, plovers, dunlin, Saunders's gull, and Falcated duck, visit the Nakatsu mudflats from various parts of the world (Akimoto, 2016).

Local people have lived in harmony with this precious mudflat for a long time. However, due to population decline (hence loss of local and traditional knowledge), climate change induced frequent extreme weather conditions, and land-use land-cover changes (industrialization and concretization), the harmony between the people and seascape, with special focus on the mudflat, is under threat. This has resulted in a decline in the aesthetic value of the mudflat as well as loss of income, from fisheries and tourism, for the local people.

After realizing the consequences of the disappearance of this vital natural resource, government agencies and all relevant stakeholders in Japan are taking the following major steps:

• Scientific investigations were conducted to assess the status quo of this ecosystem and to trace the key factors responsible for its fragmentation. Several key threats were identified: a) changes in fishing practices, including using nets with different but inappropriate mesh sizes; b) loss of the value system for the mudflat in the younger generation of local people; c) habitat encroachment through dredging and concretization; d) dredging and concretization of the shoreline for development activities; e) overexploitation of natural resources due to the evolution of technology and increases in the price of different produce; f) surface runoff from nearby agricultural fields; g) habitat destruction due to mariculture of seaweed; and h) climate change, which might be changing patterns of storms, including typhoons. Rainfall during storms has been observed to be taking place more suddenly and typhoons, which were identified as natural disturbances needed to mix the shallow seas around the mudflat, have decreased over the past decade (large typhoons come to Nakatsu once every three years or so).
• Local communities and all relevant stakeholders are being made aware of the above-mentioned issues. Different means are being taken by decision makers to increase awareness about the importance of this fragile mudflat ecosystem as well as the Do’s and Don’ts to help preserve it.
• A ‘sato-umi’ landscape approach is being adopted. In Japanese, "sato" means the area where people live, and "umi" means the sea. Nearshore and shallow marine environments that are directly linked to the wellbeing of coastal communities have recently been referred to as ‘sato-umi’ in Japan, and this approach has the potential to preserve the coastal areas as common seas. Under this approach, both biological productivity and biodiversity can increase because of better human interaction with nature. This includes the promotion of indigenous local knowledge in combination with the use of the latest valuable technologies like remote sensing and Geographical Information Systems.
• At present, very few local people prefer to eat fish over meat, which contributes to a lack of motivation to preserve this mudflat. Hence, revitalizing Japanese traditional culture, where fish is given equal dietary importance to meat, is crucial. Also, it is very important to make people aware of the sociocultural values of the Nakatsu mudflat. Studies have shown that the mudflat is of high importance in terms of ecosystem services such as aesthetic appeal, local food culture, spiritual and religious beliefs, education and knowledge (cultural ecosystem services), biomass production, water purification, sediment formation and retention, and habitat for endangered species (regulating and supporting ecosystem services).

In summary, mudflats are an ideal NbS for environmental protection against various climatic hazards, as well as serving as hotspots for biodiversity conservation, and providing recreational value and socio-economic well-being. Both institutional and policy reforms are needed to conserve tidal flat/mudflat ecosystems around the globe. Some of the key measures to achieve this could include mudflat-based tourism activities, conservation activities, seascape management, diligent monitoring, and participatory management.