Resumen del producto

The present state of deoxygenation in the northern limits of the shallow oxygen minimum zoneoff Mexico is examined in order to detect its effects on larval fish habitats and consider the sensitivity of fishlarvae to decreased dissolved oxygen. A series of cruises between 2000 and 2017 indicated a significantvertical expansion of low oxygen waters. The upper limit of suboxic conditions (<4.4 µmol/kg) has risen~100 m at 19.5°N off Cabo Corrientes and ~50 m at 25°N in the mouth of the Gulf of California. The larvalhabitat distribution was related to the geographic variability of dissolved oxygen and water masses betweenthese two latitudes. One recurrent larval habitat, with Bregmaceros bathymaster larvae as the indicatorspecies, extended throughout the water column off Cabo Corrientes from Subtropical Subsurface Water(suboxic conditions) to the surface (220 µmol/kg). The second recurrent habitat was located between theoxycline (>44 µmol/kg) and the surface in association with the Gulf of California Water, with Benthosemapanamense as the indicator species. During the warm El Niño event of 2015–2016, a tropical larval fishhabitat (Auxis spp.) associated with Tropical Surface Water appeared to change the larval habitatdistributions. These results indicate that some species are resilient to changes of dissolved oxygen andtemperature generated by El Niño events and by continuing deoxygenation, although other species withmore limited environmental windows could be affected by deoxygenation, probably leading to a change ofthe pelagic ecosystem over time.

Palabras clave: Fish Larvae Habitats; deoxygenation; Minimum oxygen zone off Mexico

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