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Gelatinous zooplankton are prominent fauna in the deep ocean, especially in the water column associated with the sea floor. This interface zone, the benthic boundary layer, is critical to biogeochemical exchanges between pelagic and benthic communities. A conspicuous member of this benthic boundary layer community in the abyssal Northeast Pacific (Sta. M; 4000 m depth) is the hydrozoan medusa, Benthocodon pedunculata. A 3-year time-series study was conducted of B. pedunculata from October 2014 to November 2017 using an autonomous time-lapse camera system and acoustic current meter deployed on the sea floor. Remotely operated vehicle benthic video transects and collections were also conducted during six servicing cruises for the long-term instruments. Over three years, a total of 123,887 B. pedunculata were recorded in hourly images with densities ranging from 0 to a high of 33 individuals m−3 in March 2016. Density of B. pedunculata was highest when current speeds were low, and declined precipitously as speed increased beyond ~1 cm s−1. Movement of B. pedunculata was parallel to the continental margin in northwest and southeast directions. The large numbers of B. pedunculata observed over this 3-year study suggests their ecological importance in the benthic boundary layer food web at Sta. M.

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 25 m to 3971 m. 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 2000 m, 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.

Since its founding, the Monterey Bay Aquarium Research Institute (MBARI) has pioneered unique capabilities for accessing the deep ocean and its inhabitants through focused peer relationships between scientists and engineers. This focus has enabled breakthroughs in our understanding of life in the sea, leading to fundamental advances in describing the biology and the ecology of open-ocean and deep-sea animals. David Packard’s founding principle was the application of technological advances to studying the deep ocean, in part because he recognized the critical importance of this habitat in a global context. Among other fields, MBARI’s science has benefited from applying novel methodologies in molecular biology and genetics, imaging systems, and in situ observations. These technologies have allowed MBARI’s bioluminescence and biodiversity laboratory and worldwide collaborators to address centuries-old questions related to the biodiversity, behavior, and bio-optical properties of organisms living in the water column, from the surface into the deep sea. Many of the most interesting of these phenomena are in the midwater domain—the vast region of ocean between the sunlit surface waters and the deep seafloor.

A study was conducted on the impacts of the presence of the Acoustic Thermometry of Ocean Climate (ATOC)/Pioneer Seamount cable on the benthos from nearshore waters adjacent to its origin at Pillar Point Air Force Station in Half Moon Bay, California to its terminus 95 km along its length on Pioneer Seamount. The coaxial Type SD cable was installed, unburied on the seafloor in 1995. Thirteen sites along the cable route were surveyed using the Monterey Bay Aquarium Research Institute (MBARI) ROVs Ventana and Tiburon equipped with cable-tracking tools. Quantitative comparisons of biological communities and seafloor features between cable and control sites were performed at nine stations. Forty-two hours of video footage and 138 push cores were collected over 15.1 km of seafloor. Approximately 12.1 km of the cable was observed (13% of the cable route). This study documents the appearance and condition of the cable and the underlying seafloor, and the effects of the cable on biological communities along its route. Limited self-burial of the cable has occurred during the 8-year deployment, particularly over the continental shelf and upper slope. Cable strumming by nearshore wave action has incised rocky siltstone outcrops. Several observations of kinks and snags in the cable on the upper slope (∼240 m depth) suggest contact with trawling gear. Few changes in the abundance or distribution of benthic fauna were detectable from video observations (epifaunal) and sediment core samples (infauna). Of 17 megafaunal groups and 19 infaunal taxa, no tests evaluating the overall effect of the cable were statistically significant. While these results indicate that the biological impacts of the cable are minor at most, three megafaunal groups exhibited cable-related changes at one or more stations. Actiniarians (sea anemones) colonized the cable when it was exposed on the seafloor, and were therefore generally more abundant on the cable than in surrounding, sediment-dominated seafloor habitats. Some fishes were also more abundant near the cable, apparently due to the higher habitat complexity provided by the cable. The study also documents general changes in the benthos across the Central California continental margin.