Larval fish abundances off southern California from 1951 to 2016

The 2014-2016 Northeast Pacific Marine Heatwave (MHW) induced the warmest 3-year period on record in the California Current Ecosystem. We tested whether larval fish assemblage structure, phenology and diversity dynamics were comparable to past warming events from 1951-2013. First, we hypothesized, based on past observations of biological effect of warming, that mesopelagic species with southern distributions relative to southern California and Pacific sardine Sardinops sagax (a coastal pelagic species) would increase during the MHW while northern mesopelagics and northern anchovy Engraulis mordax (coastal pelagic) abundances would decline. Similar to past warming, southern mesopelagics increased and northern mesopelagics decreased. Unexpectedly, however, a common southern mesopelagic, Mexican lampfish Triphoturus mexicanus, was approximately three times more abundant than the previous annual high. Further, whereas sardine abundance did not increase, larval anchovy abundance rose to near...