Small autonomous landers for studying the community ecology of nearshore submarine canyons

Abstract

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 developed two autonomous lander systems: a 2-sphere Picolander for exploratory deployments (< 3 days) and a 3-sphere Nanolander for longer deployments (> 1 week). Both landers were outfitted with a camera and lights system and a ZebraTech environmental sensor and collected 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. We found that communities at 100 and 500 m were distinct from all other depths while the 300 m community was transitional between these depths and had the highest diversity, despite unexpectedly high turbidity. Additionally, we recorded clear diurnal patterns in fishes deeper than 300 m, as well as vertical migration of larval flatfish. This study also aimed to document the number and area of small submarine canyons off the coast of California and determine the extent of government protection of both large and small canyons. Small canyons were defined as features with a minimum depth of 200 m and incised 100 m 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 were 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