Doliolid (Tunicata, Thaliacea) Blooms in the Southeastern Gulf of Alaska as a Result of the Recent Marine Heat Wave of 2014–2016

Alexei I Pinchuk,Sonia D Batten,Wesley W Strasburger

doi:10.3389/fmars.2021.625486

Abstract

The eastern North Pacific experienced a prolonged heat wave in 2014–2016 manifested by high sea surface temperature anomalies in the south-central Gulf of Alaska (GOA). The event provided a natural experiment on the response of the southern GOA ecosystem to a dramatic change in sea temperature. Spatial and temporal variability in zooplankton communities following the culmination of the heat wave was investigated as a part of the NOAA Eastern GOA Ecosystem Assessment program in 2016–2017. Here, for the first time in the GOA, we report consistent observations of doliolid (Dolioletta tritonis) swarms observed in the upper mixed layer beyond the shelf break during both years, with the maximal density of 3,847 ind m–3recorded in August 2016 and coinciding with the location of an offshore cyclonic mesoscale eddy. Doliolid density was significantly lower on the shelf. The long-term Continuous Plankton Recorder (CPR) data indicated that doliolid blooms in the south-central GOA may have occurred in the past two decades during El-Nino events. Coincidentally, doliolids prevailed in the diets of juvenile sablefish collected along the eastern coast of GOA both during the 2014–2016 heat wave and during 1997–1998 El Nino. Thus, we speculate that warming trends may increase the importance of doliolids in the GOA pelagic food web.

Highlights

Ecological impacts of climate change have become increasingly apparent affecting the organizational hierarchy of species and communities with marine ecosystems (Walther et al, 2002)
For the first time in the Gulf of Alaska (GOA), we report consistent observations of doliolid (Dolioletta tritonis) swarms observed in the upper mixed layer beyond the shelf break during both years, with the maximal density of 3,847 ind m−3 recorded in August 2016 and coinciding with the location of an offshore cyclonic mesoscale eddy
We report the first observation of intense D. tritonis bloom in the southeastern GOA during the 2016–2017 heat wave and utilize long-term data sets and historical data to link doliolid emergence in the southeastern GOA to climate variability

Summary

Introduction

Ecological impacts of climate change have become increasingly apparent affecting the organizational hierarchy of species and communities with marine ecosystems (Walther et al, 2002). The ecosystem impacts of these climate events can be severe resulting in shifts in geographical distributions and seasonal cycles and production of marine organisms, adversely affecting human activities (Uye, 2008; Purcell, 2012; Mills et al, 2015). Such extreme events can be viewed as climate change “stress-tests,” providing insight into possible changes in ecosystem structure, species’ abundance and distribution, and the frequency and strength of ecosystem disruptions. In order to maintain resilient and sustainable marine ecosystems, it is imperative that management and conservation strategies are developed to mitigate and/or adapt to these impacts.

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Conclusion