The role of bioerosion in the coastal dynamics of a small Maldivian island

The Maldives Archipelago is currently facing a precarious phase marked by significant coastal modifications resulting from the impacts of tourism and local development. The escalating climate crisis further exacerbates the negative consequences of these coastal alterations, particularly in terms of coral bleaching events and sea level rise. This research specifically delves into the evaluation of coastal dynamics, including bioerosive processes, at Vavvaru Island in the Lhaviyani Atoll, North Province, Maldives, serving as a pilot study. The small Vavvaru Island is grappling with pronounced coastal dynamics. The northeast side, exposed to the open ocean, is undergoing rapid and continuous physical erosion, coupled with substantial sand displacement during the monsoon inversion. The northeastern reef features a substantial amount of coral rubble, hosting a well-organized community of endolithic bioeroders, extensively examined within the lagoon. More than 80% of coral fragments longer than 20 cm exhibit the presence of boring organisms. Sponges, molluscs, and worms exhibit differing temporal scales of colonization, hinting at the potential age of the fragments. Originating from the external reef crest, a gradient in the composition of the borer community is evident from the crest to the shore. Sponges and worms consistently inhabit the fragments, while molluscs gain importance closer to the island where coral fragments are more stable due to reduced water movement and minimal rolling of rubble. Our analysis emphasises the pivotal role of sponges, particularly evident in the examination of chips and spicules containing sediments. In the fine fraction of sediments, chips constitute approximately 2-10% of the total sediment. Both physical and biological disturbances impact the structure of the reef surrounding the island. The results highlight how sand movements are part of long-term dynamics affecting coral reef integrity and triggering an intense bioerosive activity. Understanding these pronounced erosive processes is fundamental for the conservation of Maldivian reefs.