Lander Lab #2: Small Autonomous Landers for Studying the Community Ecology of Nearshore Submarine Canyons
Lander Lab will routinely feature field work by researchers from around the world using ocean landers. We begin with the 2021 Scripps Institution of Oceanography/UCSD work of Ashley Nicoll, currently a PhD student at Stony Brook University, Stony Brook, Long Island, New York. Click here to see Ashley’s full Master’s Thesis paper, “Nicoll Thesis 2021.pdf”.
Nearshore submarine canyons are unique features that bring the deep sea close to shore, potentially functioning as highways connecting shallow and deep-sea ecosystems. To study their ecology, we adapted two autonomous lander systems: a Global Ocean Design® LLC 2-sphere Picolander® for exploratory deployments ( 1 week). Both landers were outfitted with a novel self-recording digital camera and LED lights system plus a Zebra-Tech® environmental sensor to collect paired physical and biological time series. Eleven lander deployments were completed ranging in length from 1-13 days at depths of 90-500 m, allowing assessment of how seafloor community diversity and composition changed with depth and time of day.
This study also aimed to document the number and area of small submarine canyons off the coast of California. Small canyons are defined as features with a minimum depth of 200m and incised 100m into the slope. Applying this, 23 small canyons were identified, with features concentrated on the Central and Southern coast. By area, 27% of large canyons and 23% of small canyons are protected, with the inshore reaches of canyons receiving more protection than offshore.
Because landers collect paired biological and physical data in hard to access areas, they may serve as powerful tools to inform management of these poorly studied deep-water habitats.
About Submarine Canyons
Scripps professor Francis Shepard defined submarine canyons as “steep-walled, sinuous valleys with V-shaped cross sections, axes sloping outwards as continuously as river-cut land canyons and relief comparable to even the largest of land canyons.” Submarine canyons throughout the U.S. Exclusive Economic Zone (EEZ) and beyond are typically understudied because they are difficult areas to access due to their depths, narrow structure, and proximity to shore. Despite being understudied, these are not rare ecosystems. Professor Ulla Fernandez-Arcaya, Centre Oceanogràfic de Balears, Instituto Español de Oceanografía, Palma, Spain, identified over 9,000 large canyons that cover approximately 11.2% of continental slopes globally. One may presume smaller canyons are more prolific. On the Pacific coast of North America, submarine canyons cut over 20% of the continental shelf on average, and approach 50% at latitudes north of 45 degrees.
Methodology to Study Submarine Canyons
Traditional deep-sea study methods include ROVs, towed cameras on sleds, or trawls, which typically require a medium or a large vessel equipped with an A-frame plus a winch with a slip ring and hundreds of meters of EM cable. The usage of such vessels is costly, time consuming, and logistically complicated when close to shore.
The biology of the deep-sea is traditionally studied using trawls. Because canyons are constricted areas with significant relief, trawls are both destructive and subject to getting caught in rocky outcroppings. In order to avoid dangers associated with trawling complex underwater features, autonomous lander systems can be used to collect environmental and biological data in small nearshore submarine canyons with greatly reduced costs and environmental impact.
This study aims to use the La Jolla Canyon as a testbed for using ocean landers as a tool to study nearshore submarine canyons.
Landers
Two low-cost, spatially flexible autonomous lander systems were used: a Global Ocean Design® LLC Nanolander® Deep Ocean Vehicle (DOV) BEEBE and Picolander® DOV LEVIN (Fig. 2). The Nanolander has three spherical housings containing a camera system, an EdgeTech® BART© (Burnwire Acoustic Release Transmitter) acoustic communication system. A Zebra-Tech™