Onshore investigation of intertidal to subtidal mass benthic mortality assemblage: Preliminary assessment of the rocky reef coastline uplifted by the 2024 Noto Peninsula Earthquake (M7.6)

Abstract

The sudden coastal uplift resulting from the 2024 Noto Peninsula earthquake exposed the previously subtidal and intertidal habitats, providing a unique opportunity to document the biotic community and immediate effects of geological disturbances on it. This study describes the characteristics of the benthic death assemblages around the Kaiso fishing port, which experienced approximately 3.6–3.9 m of uplift, with special attention to the vertical distribution of coastal benthos inhabiting Kaiso Reef. Our field surveys were initiated 66 days after the earthquake, integrating quadrat-based sampling with direct observation of emergent marine habitats. 92 molluscan and 5 echinoderm species were found in our quadrat investigation. The soft tissues of most molluscan individuals remained, indicating that their in situ life postures were undisturbed. Given this premise, species richness was estimated to have peaked between the pre-disaster middle to lower intertidal and uppermost subtidal zones, particularly in areas with reduced wave exposure. Additionally, the surveys identified several notable species at the Kaiso fishing port, including the Near-Threatened coral Oulastrea crispata and bivalve Pinna bicolor, both of which have their northernmost records in the Sea of Japan from the Noto area. The uplifted zone presents a rare opportunity to examine the subtidal fauna from terrestrial vantage points, yielding novel perspectives on marine biodiversity in the Sea of Japan. Also, these findings provide critical baseline data for monitoring post-uplift ecological succession against a backdrop of ongoing climate change.