Local oceanographic conditions link predator-prey dynamics from surface waters to the deep ocean

Abstract

Offshore pelagic environments are dynamic and rich in biodiversity, yet our understanding of these habitats is lacking as they are surveyed less frequently than coastal areas. We present results from one-year (October 2016i–October 2017) of comprehensive oceanographic mooring measures from a site located 150 nmi offshore Southern California in abyssopelagic waters, spanning water mass, nutrient, primary productivity, fish, and cetacean variables. We identified abrupt changes in water properties, bringing distinct biological communities to our site. Some examples were active acoustically observed backscatter from diel vertical migrators, present during parts of summer and throughout fall, coincided with passive acoustically measured night-time echolocation of common dolphins (Delphinus delphis). Risso’s (Grampus griseus) and Pacific white-sided dolphin (Lagenorhynchus obliquidens) echolocation was also coincident with near-surface backscatter but during winter and early spring. Backscatter during that time was predominantly from small pelagic fishes, as diel vertical migration was virtually absent. Echolocation from Cuvier’s beaked whales was prominent during winter and spring, associated with colder water from the California Current, but were absent in early summer when the water in the deep sea abruptly warmed. This study demonstrates how local oceanographic conditions link predator-prey dynamics from surface waters to the deep sea.