Putting the Pacific marine heatwave into perspective: The response of larval fish off southern California to unprecedented warming in 2014–2016 relative to the previous 65 years

Abstract

The 2014-2016 Northeast Pacific marine heatwave (MHW) induced the warmest 3year 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 to 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. Furthermore, whereas sardine abundance did not increase, larval anchovy abundance rose to near-record highs in summer 2016. Second, we hypothesized that fishes would spawn earlier during the MHW. Fishes did not spawn in an earlier season within a year, but five of six southern mesopelagic taxa spawned earlier than typical within winter and spring. Third, we predicted that species richness would increase moderately due to an influx of southern and exodus of northern species. Richness, however, was very high in all seasons and the highest ever during the summer as multiple species with primarily southern distributions were recorded spawning for the first time in southern California. The richness of northern species was also unexpectedly high during the MHW. Northern species likely persisted in the study area because in addition to the warm water, pockets of cold water were consistently present. If, as predicted, conditions similar to the MHW become more common as oceans warm, this unique and largely unexpected combination of fishes may reflect future biological conditions.

Message in a Bottle: Archived DNA Reveals Marine Heatwave-Associated Shifts in Fish Assemblages

“…However, our findings and others (Checkley et al, 2017;McClatchie, 2012;Nielsen et al, 2021;Thompson, Harvey, et al, 2019) suggest that the mechanisms that govern the population dynamics of these species are not a mere function of temperature, but that more complex factors drive recruitment dynamics of these species (Thompson et al, 2022a). For example, despite largely synchronous responses of fish assemblages to the marine heatwave, sardine declines were not consistent across the CCLME (Figure 3), with refugia of localized abundance in nearshore waters potentially driven by distinct, favorable conditions (Checkley et al, 2017;Sydeman et al, 2020;Thompson et al, 2022a).…”

“…Smith, and L.E. Eber, 1987; H. Moser et al, 2001; H. G. Moser et al, 1993; Thompson et al, 2022a) indicate the majority of species spawn in spring and the resulting ichthyoplankton closely track adult biomass (Hsieh et al, 2005). Hence, we expect the spring ichthyoplankton to reflect underlying changes in the local fish assemblages.…”

“…For example, ichthyoplankton assemblages differ among the colder and fresher California Current, warmer and saltier California Counter Current and Central Pacific water mass, and in upwelling conditions across the continental shelf (Asch, 2015; Lindegren et al, 2013; Smith & Moser, 2003; Snyder et al, 2003). Importantly, periods of elevated temperatures were historically associated with higher abundances of southern, mesopelagic species and Pacific Sardine while colder periods were associated with higher abundances of northern, mesopelagic species and Northern Anchovy ( Engraulis mordax ) (Chavez et al, 2003; Thompson et al, 2022)(Chavez et al, 2003; Thompson et al, 2022a). These insights into forage-fish community dynamics across decadal climatic regime shifts are vital to understanding the effects of climate change on the CCLME (Asch, 2015; Checkley et al, 2017; Lindegren et al, 2013).…”

Kelpwatch: A new visualization and analysis tool to explore kelp canopy dynamics reveals variable response to and recovery from marine heatwaves

“…Latitudinal trends in resistance and resilience were examined using Pearson correlations, a constant value of 1% was added, and values were log transformed to meet the assumptions of the model. To put the effects of the unprecedented marine heatwaves into historical perspective [9], mean kelp canopy area since the beginning of the heatwave events (2014 to 2021) was compared to the historical mean canopy area from 1984 to 2013 for each 10…”

Fisheries Surveys Are Essential Ocean Observing Programs in a Time of Global Change: A Synthesis of Oceanographic and Ecological Data From U.S. West Coast Fisheries Surveys

“…Species such as Pacific Sardine were observed spawning in the winter for the first time off Oregon (Auth et al, 2018). In central and southern California, abundances of southern, mesopelagic taxa were at record highs both in RREAS (Sakuma et al, 2016;Thompson et al, 2019b) and CalCOFI larval surveys (Thompson et al, 2021), which is consistent with past warm water events (Peabody et al, 2018). Atypically, Northern Anchovy (Thompson et al, 2019b) and multiple rockfishes (Schroeder et al, 2019) that previously flourished under cold conditions had extremely high recruitment from 2014 to 2016, and adult abundances of anchovy rose to record highs in subsequent years (Auth et al, 2018;Thompson et al, 2019b).…”