Challenges in assessing intertidal habitats in temperate estuaries and coasts in Japan.

Abstract

This paper addresses future challenges related to the quantitative assessment of intertidal habitats, particularly tidal flats and salt marshes, with the aim of conserving estuarine and coastal biodiversity in Japan. Approximately 40% of tidal flats in Japan have been lost since 1945, and the decline has been mainly observed in the foreshore. Quantification of the tidal flats in riverine areas has not performed in depth and is necessary. Intertidal habitats covered with gravelly sediments formed in riverine areas have unique estuarine ecosystems based on the topographic and basin characteristics of Japanese small islands. However, these habitats may be overlooked in the quantification via the habitat assessment system developed recently. Although salt marshes, including reed beds, have been severely degraded and lost due to anthropogenic impacts, this decline throughout Japan has not been assessed. Therefore, we must first address the lack of fundamental data on salt marshes for their effective conservation and restoration planning. Small patches of salt marshes located in small basins should be quantitatively assessed because no significant positive correlation was observed between the area of salt marshes and species richness; i.e., these patches are expected to contribute to biodiversity conservation. Furthermore, adequate biodiversity assessment is difficult using a single evaluation item, such as “tidal flats” or “reed marshes”, because the biota in intertidal habitats is diversified according to biotic and abiotic factors. Developing field-applicable survey methods with simple, rapid, and inexpensive techniques is needed to quantify intertidal habitats or evaluate the current status of a threatened species in more detail. The study of new survey gears and analytical techniques will support this development.