Cold Regime interannual variability of primary and secondary producer community composition in the southeastern Bering Sea.

Beth A Stauffer,Joaquim I Goes,Jennifer Miksis-Olds,Arga Chandrashekar Anil

doi:10.1371/journal.pone.0131246

Beth A Stauffer, Joaquim I Goes + Show 2 more

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https://doi.org/10.1371/journal.pone.0131246

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Abstract

Variability of hydrographic conditions and primary and secondary productivity between cold and warm climatic regimes in the Bering Sea has been the subject of much study in recent years, while interannual variability within a single regime and across multiple trophic levels has been less well-documented. Measurements from an instrumented mooring on the southeastern shelf of the Bering Sea were analyzed for the spring-to-summer transitions within the cold regime years of 2009–2012 to investigate the interannual variability of hydrographic conditions, primary producer biomass, and acoustically-derived secondary producer and consumer abundance and community structure. Hydrographic conditions in 2012 were significantly different than in 2009, 2010, and 2011, driven largely by increased ice extent and thickness, later ice retreat, and earlier stratification of the water column. Primary producer biomass was more tightly coupled to hydrographic conditions in 2012 than in 2009 or 2011, and shallow and mid-column phytoplankton blooms tended to occur independent of one another. There was a high degree of variability in the relationships between different classes of secondary producers and hydrographic conditions, evidence of significant intra-consumer interactions, and trade-offs between different consumer size classes in each year. Phytoplankton blooms stimulated different populations of secondary producers in each year, and summer consumer populations appeared to determine dominant populations in the subsequent spring. Overall, primary producers and secondary producers were more tightly coupled to each other and to hydrographic conditions in the coldest year compared to the warmer years. The highly variable nature of the interactions between the atmospherically-driven hydrographic environment, primary and secondary producers, and within food webs underscores the need to revisit how climatic regimes within the Bering Sea are defined and predicted to function given changing climate scenarios.

Highlights

The Bering Sea ecosystem is of significant economic importance as the source for over 40% of finfish and shellfish landings, in biomass, in the United States [1]
Signs of warming have become apparent in the northern Bering Sea and Arctic, with significant decreases observed in mean annual sea ice extent since 1979 and 1998 in the Chirikov Basin [4] and Arctic Ocean [5], respectively, and a 27% increase in annual mean open-water area since 1998 in the Arctic Ocean [6]
Multivariate cluster and multidimensional scaling (MDS) analyses indicate that the spring-summer environment in 2012 was significantly different (p < 0.05) from the environment in the other three years which were largely similar to one another (Fig 3)

Summary

Introduction

The Bering Sea ecosystem is of significant economic importance as the source for over 40% of finfish and shellfish landings, in biomass, in the United States [1]. Some of the major differences in Bering Sea ecosystem function during warm years (relative to cold) include: delayed timing of the spring phytoplankton bloom; shifts in zooplankton consumer populations with reduced populations of large copepods; and transport of the resulting biomass to pelagic rather than benthic fishery populations. These effects, among many others, were summarized by Hunt et al (2002) in the Oscillating Control Hypothesis (OCH) to explain the ecological dynamics associated with each climatic regime [7]. This hypothesis has been revised since its original inception to incorporate evidence for a lack of large zooplankton in warm years [1,8,11], despite increased primary production [12]

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