Marine clean-up dives remove more than just marine litter

Ecological transformation is underway on Caribbean reefs, including the flattening of structural complexity and shifts in species assemblages. As marine litter accumulates faster than it can be removed, marine organisms increasingly use litter for shelter and substrate. This study used commercial litter removal dives to assess the cryptofauna most affected by such activities. Following state and federal protocols, displaced taxa were recorded from marine litter retrieved during 18 dive events. Mobile organisms, stony corals, and soft corals were classified, with polychaete worms, Scleractinia corals, and crustaceans (e.g., Mithracidae crabs) comprising over 58% of all taxa observed. Taxa exhibited various interactions with specific litter types. Dives with more diverse litter types yielded significantly higher cryptofauna richness. Biomass estimates were calculated using length- or width-weight relationships for taxa found on the four most abundant litter types (plastic, cloth, metal, processed wood). Using medians and best-fit models for 21 identified taxa, the 18 dives removed an estimated total biomass of 1.34 kg. This equates to roughly 0.0014 kg of fauna per kilogram of litter. When scaled to PADI AWARE Dive Against Debris® removals specific to coral reef environments within the Florida Keys National Marine Sanctuary, we estimate that over 94 kg of biomass of taxa may have been removed over the past decade. These values likely underestimate the true impact especially once scaled to the many clean-up dives that occur each year. We recommend that conservation and management practices account for these largely understudied taxa. Further observations of litter-cryptofauna interactions will improve our ability to include taxon-specific impact estimates in past and future marine litter removal efforts.