Paralarvae of the complex Sthenoteuthis oualaniensis-Dosidicus gigas (Cephalopoda: Ommastrephidae) in the northern limit of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean (April 2012)

The three-dimensional distribution of the paralarvae of the complex Sthenoteuthis oualaniensis-Dosidicus gigas (Cephalopoda: Ommastrephidae) was analyzed at the northern limit of the shallow oxygen minimum zone in the Eastern Tropical Pacific in April 2012. The upper limit of the oxygen minimum water (∼44 μmol/kg or 1 mL/L) rises from ∼100 m depth in the entrance of the Gulf of California to ∼20 m depth off Cabo Corrientes. Most of the paralarvae of this complex, dominated by D. gigas, were concentrated in the Gulf entrance, between the thermocline (∼20 to ∼50 m depth) and the sea surface, in the warmest (>19°C) oxygenated (>176 μmol/kg) layer. The highest abundance of paralarvae was detected in an anticyclonic eddy (∼120 km diameter and >500 m deep), which contained lower-salinity water (<35 g/kg), consistent with formation in the California Current. Lower paralarvae abundance was recorded further south off Cabo Corrientes, where hypoxic layers were elevated as water shoaled nearshore. Almost no paralarvae were found in the north of the study area beyond the strong salinity front (∼34.8-35.4 g/kg) that bounded the anticyclone. These results showed an affinity of the paralarvae for lower-salinity, oxygenated water, illustrated by the influence of the mesoscale anticyclonic eddy and the salinity front in their distribution. Based on this study, it can be concluded that the expansion of the depth range of hypoxic water observed in the Eastern Tropical Pacific may be increasing environmental stress on the paralarvae by vertically restricting their habitat, and so affecting their survival.