Long-term coastline monitoring on a coral reef island (Moorea, French Polynesia)

Abstract

While many monitoring programs on coral reefs (for lagoons and outer slopes) exist in the South Pacific, there are no observatories dedicated to monitoring the coastline, a small strip of land and sea upon which many environmental and economic issues coincide. The present study compares the extent of coastline modification at Moorea Island (French Polynesia) between 1977 and 2018. Our coastal monitoring highlighted a strong increase in artificial embankments, and a decrease in beach-dominated coast from 1977 to 2009. From 2009 to 2018, the percentage of embankments have been relatively stable. However, we observed 20% of beach-dominated coast without high vegetation in 2009 and only 10% in 2018. Furthermore, we found that 12% of beach-dominated coast with coarse mud and detrital substrate in 2009 and 22% in 2018. These findings highlighted that anthropogenic factors were principal drivers of coastline changes at Moorea Island. In order to inform conservation and management strategies for coastlines in the South Pacific Islands, it is imperative to conduct ongoing monitoring of coastlines through the creation of dedicated coastline observatories. This work will enhance our understanding of the impact of human-induced environmental changes on this ecologically, economically and culturally important ecosystem.