Floating objects in the open ocean: Unveiling modifications of the pelagic habitat induced by forest cover change and climate variations

Abstract

Natural floating objects (NLOGs) are a major component of the habitat of pelagic species. Since the 1990s, the number of floating objects in the open ocean has increased greatly as a result of the introduction of drifting fish aggregating devices (DFADs) by the industrial tropical tuna purse seine vessels. These changes, and their potential impacts on the species that associate with floating objects, remain poorly understood. If the habitat modifications induced by DFADs have been recently characterized and quantified, the impact of other human activities on the number of floating objects is poorly studied. Relying on lagrangian simulations at the scale of the whole Indian Ocean, from 2000 to 2019, we assess the potential modifications of the pelagic surface habitat that could originate from forest cover change and climate variations. We develop several scenarios, based on coastal and river forest cover, precipitations and river discharge, to simulate densities of NLOGs. Our results suggest no significant increase in average NLOG densities in the ocean and highlight important regional and seasonal variations of these densities driven by both forest cover change and precipitations. These preliminary findings underscore the limited understanding of this critical element of pelagic species habitat. Therefore, there is pressing need to intensify monitoring efforts for pelagic species habitat and raise awareness about potential impacts of habitat modifications on tuna and other pelagic species.