Interannual response of euphausiid community abundance during the anomalous warming period (2014–2016) in the Gulf of California

El Niño in the northeast Pacific and Gulf of California typically causes a decrease in euphausiid abundance (biomass), and modifies their latitudinal biogeographic distributions, but the effect of recent marine heat waves (or their combined effect with El Niño) are less understood. The interannual response of euphausiid community structure and abundance were investigated during the cold–warm transition period (June) of six years (2013–2019, except 2015) in the central Gulf of California, Mexico. Abundance in June 2013–2019 was compared with historical baseline for euphausiid abundance made in June 1957 from a California Cooperative Oceanic Fisheries Investigation cruise, just before El Niño 1957–1958. During 2014–2019 two anomalously warm events occurred: the marine heat wave of 2014 (MHW 2014) and El Niño 2015–2016 (May 2015–May 2016). We tested the hypothesis that the numerically dominant subtropical neritic species Nyctiphanes simplex and temperate oceanic Nematoscelis difficilis significantly decrease in abundance in response to the prolonged warming that occurred during 2014–2016 and that tropical euphausiid species could increase in relative abundance during this period. Ten euphausiid species were collected accounting for < 3% of total relative abundance of 34 zooplankton taxonomic groups collected during June 2013–2014, 2016, 2018 and between 7 and 22.4% during 2017 and 2019. N. simplex and Ne. difficilis accounted for > 80% of euphausiid total abundance during June 2013–2019, with considerably lower abundance during 2013, the MHW 2014, and El Niño 2015–2016 than in June 2017, 2018, and 2019. Mean euphausiid abundance in 2017 and 2019 was slightly higher than that recorded in June 1957. Tropical species increased their relative abundances during El Niño 2015–2016 event, but they were always < 15% of total euphausiid relative abundance during 2013–2019. We estimated that it took at least 3 years for the euphausiid species abundance in the gulf to slowly recover from the unfavorable conditions associated with MHW 2014, and El Niño 2015–2016 to attain highest mean abundance in 2019. Multi–variated ordination analyses showed that the prolonged warming and anomalously low Chl-a concentrations recorded in 2014–2016 negatively influenced euphausiid abundance, a proxy for euphausiid biomass available for pelagic predators in the Gulf of California.