Debris in the deep: Using a 22-year video annotation database to survey marine litter in Monterey Canyon, central California, USA

Anthropogenic marine debris is an increasing concern because of its potential negative impacts on marine ecosystems. This is a global problem that will have lasting effects for many reasons, including: (1) the input of debris into marine environments is likely to continue (commensurate with population increase and globalization), (2) accumulation, and possibly retention, of debris will occur in specific areas due to hydrography and geomorphology, and (3) the most common types of debris observed to date will likely persist for centuries. Due to the technical challenges and prohibitive costs of conducting research in the deep sea, little is known about the abundance, types, sources, and impacts of human refuse on this vast habitat, and the extreme depths to which this debris is penetrating has only recently been exposed. We reviewed 1149 video records of marine debris from 22 years of remotely operated vehicle deployments in Monterey Bay, covering depths from 25m to 3971m. We characterize debris by type, examine patterns of distribution, and discuss potential sources and dispersal mechanisms. Debris was most abundant within Monterey Canyon where aggregation and downslope transport of debris from the continental shelf are enhanced by natural canyon dynamics. The majority of debris was plastic (33%) and metal (23%). The highest relative frequencies of plastic and metal observations occurred below 2000m, indicating that previous studies may greatly underestimate the extent of anthropogenic marine debris on the seafloor due to limitations in observing deeper regions. Our findings provide evidence that submarine canyons function to collect debris and act as conduits for debris transport from coastal to deep-sea habitats.