Gauging oxygen risk and tolerance for the megafauna of the Southern California shelf based on in situ observation, species mobility, and seascape

Oxygen decline poses increasing risks to global shelf communities. This study was conducted to measure species oxygen exposures in situ and to assess risks of low oxygen based on the hypothesis that species risk varies spatially and is dependent on the interaction of shelf oxygen dynamics with habitat pattern, species mobility, and tolerance to low oxygen. Here, we report concomitant observations of oxygen, depth, and habitat for the most common benthic and epibenthic megafauna on the southern California shelf (30-125 m). The study was conducted when oxygen concentrations were the lowest observed within the previous 30 years off southern California (2012-2014), yet hypoxic conditions (<1.42 ml l(-1)) were not observed. No significant oxygen exposure differences were observed among highly mobile, mobile, and sessile species due to the dynamic nature of the oxycline. Habitat affinities for the most abundant benthic megafauna (53 taxa) were discriminated among four different habitats. Highly mobile rockfish (Sebastidae) exhibited distributions suggesting less tolerance to low oxygen than most other taxa. Given the mosaic of consolidated and coarse-grained habitats that rockfish prefer, the onset of hypoxic conditions near the shelf break (similar to 90-120m) would likely compress local rockfish populations into less favourable habitat in a non-linear fashion.