Contrasting diversity patterns using Autonomous Reef Monitoring Structures deployed in pelagic vs. benthic environments

Abstract

Recent developments of data-driven standardized sampling tools have reduced knowledge gaps on benthic biodiversity and larval dispersal patterns. Here, we present a new application to estimate benthic spatial biodiversity patterns and evaluate potential larval dispersal from nearshore coast to the pelagic environment. To do so, we combined DNA metabarcoding and imagery on Autonomous Reef Monitoring Structures (ARMS) deployed in pelagic and nearshore benthic systems across the Bay of Biscay's Basque Coast. Results reveal a remarkably lower biodiversity in pelagic relative to benthic ARMS as well as strong spatial patterns in community composition with the pelagic ARMS greatly differing to the benthic ones according to both metabarcoding (ANOSIM R = 0.82; p = 0.002) and image analysis (ANOSIM R = 0.87; p = 0.001). We also show that a large portion of the larvae inhabiting the pelagic domain (83.5\%) probably originates from benthic habitats, while the benthic community shared across pelagic and benthic habitats is considerably lower (24.9\%). Further, we also analyzed which benthic species successfully use the pelagic environment to disperse across the ocean from nearshore coast, and found that the unique benthic taxa inhabiting the pelagic ARMS consist of organisms with typically larger dispersal distances relative to strictly sessile taxa with direct larvae development found only in rock-attached benthic ARMS. Overall, these findings suggest that the benthic system acts as population source delivering species towards a less diverse pelagic domain. Taken together, this novel application of ARMS deployed in pelagic systems has the potential to identify the often overlooked yet critically important benthic community structure, as well as to unveil how dispersal pathways across benthic and pelagic habitats can shape biodiversity patterns of coastal ecosystems