Responses of ichthyoplankton assemblages to the recent marine heatwave and previous climate fluctuations in several Northeast Pacific marine ecosystems

Abstract

The effects of climate warming on ecosystem dynamics are widespread throughout the world's oceans. In the Northeast Pacific, large‐scale climate patterns such as the El Niño/Southern Oscillation and Pacific Decadal Oscillation, and recently unprecedented warm ocean conditions from 2014 to 2016, referred to as a marine heatwave (MHW), resulted in large‐scale ecosystem changes. Larval fishes quickly respond to environmental variability and are sensitive indicators of ecosystem change. Categorizing ichthyoplankton dynamics across marine ecosystem in the Northeast Pacific can help elucidate the magnitude of assemblage shifts, and whether responses are synchronous or alternatively governed by local responses to regional oceanographic conditions. We analyzed time‐series data of ichthyoplankton abundances from four ecoregions in the Northeast Pacific ranging from subarctic to subtropical: the Gulf of Alaska (1981–2017), British Columbia (2001–2017), Oregon (1998–2017), and the southern California Current (1981–2017). We assessed the impact of the recent (2014–2016) MHW and how ichthyoplankton assemblages responded to past major climate perturbations since 1981 in these ecosystems. Our results indicate that the MHW caused widespread changes in the ichthyoplankton fauna along the coast of the Northeast Pacific Ocean, but impacts differed between marine ecosystems. For example, abundances for most dominant taxa were at all‐time lows since the beginning of sampling in the Gulf of Alaska and British Columbia, while in Oregon and the southern California Current species richness increased as did abundances of species associated with warmer waters. Lastly, species associated with cold waters also increased in abundances close to shore in southern California during the MHW, a pattern that was distinctly different from previous El Niño events. We also found several large‐scale, synchronized ichthyoplankton assemblage composition shifts during past major climate events. Current climate projections suggest that MHWs will become more intense and thus our findings can help project future changes in larval dynamics, allowing for improved ecosystem management decisions.

Tracking and forecasting community responses to climate perturbations in the California Current Ecosystem

“…Several studies have documented myriad biological responses to this event. For example, within the California Current Ecosystem (CCE), there were mass strandings of marine mammals [17], increased whale entanglements due to shifting prey sources [18], mass mortality events for marine seabirds [17,19,20], a record-breaking domoic acid outbreak [21], shifts in pelagic macronekton and micronekton communities and species richness [22][23][24], irruptions of previously rare fishes and invertebrates throughout the California Current [25][26][27][28], and extraordinarily high recruitment of rockfishes (genus Sebastes) [29,30] and northern anchovy (Engraulis mordax) [31]. Yet, to date, there have been few quantitative studies of how the marine heatwave impacted the broader CCE community at multiple trophic levels, and therefore the importance of this extreme event for communitywide patterns of variability, and the persistence of the community response, remains largely unknown.…”

Physiological acclimatization in high‐latitude zooplankton

“…It had devastating effects on fisheries and wildlife along the entire Gulf of Alaska, Bering Sea and even the southern California Current System (Peterson et al, 2015). The weather‐induced environmental changes cascaded through the entire food web with reports of low primary productivity, unusual harmful algal blooms, warm‐water copepod species invading the subarctic, low larval fish recruitment, and high mortality in salmon, sea birds, whales and sea lions (Auth et al, 2018; Gomez‐Ocampo et al, 2018; Nielsen et al, 2021; Piatt et al, 2020; Rogers et al, 2021; Suryan et al, 2021; Zhu et al, 2017). However, an analysis of abundance data of the pelagic community collected over a 20‐year period in the Gulf of Alaska underscored the difficulty of understanding causal effects.…”

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

“…The unprecedented physical oceanographic anomalies associated with the CCE 2014-2016 MHW induced biological changes at multiple trophic levels (Cavole et al, 2016). For example, there was a large increase in harmful algal blooms (McCabe et al, 2016;Ryan et al, 2017); decreased primary production (Kahru et al, 2018;Morrow et al, 2018); and abrupt changes in phytoplankton (Du & Peterson, 2018), zooplankton (Brodeur et al, 2019;Peterson et al, 2017), pelagic invertebrate (Brodeur et al, 2019;Van Noord & Dorval, 2017), ichthyoplankton (Auth et al, 2018;Nielsen et al, 2021) and recently recruited fish (Basilio et al, 2017;Santora et al, 2017;Schroeder et al, 2019) assemblages. At higher trophic levels, top predators displayed emaciated body condition and/or increased mortality (Laake et al, 2018;S.…”

“…McClatchie et al, 2016;Piatt et al, 2020;Robinson et al, 2018). In addition to impacting the CCE, the MHW greatly affected the Gulf of Alaska as larval abundances of most fishes were very low (Nielsen et al, 2021), the body size of a key forage fish, Pacific sand lance Ammodytes personatus was much reduced relative to recent cool years (von Biela et al, 2019), and adult abundance of ecologically and commercially important Pacific cod Gadus microcephalus plummeted immediately following the MHW (Barbeaux et al, 2020). Although these studies help elucidate biological changes during the 2014-2016 MHW, it is difficult to evaluate the degree to which these occurrences were unusual because the temporal duration of analyzed time series ranged only from 2 to 32 years prior to 2016.…”

“…Based on observations of the impacts of warming events on fish larvae in the CCE (Auth et al, 2018;Nielsen et al, 2021) and around the world (Catalan et al, 2006;Keane & Neira, 2008), we developed specific hypotheses regarding responses of assemblage structure, phenology, and richness to the MHW. First, taxa that have similar spatial distributions and/or adult habitat often respond similarly to changes in oceanographic conditions (Hsieh et al, 2009;Thompson et al, 2012).…”