Small pelagics in a changing ocean: biological responses of sardine early stages to warming.

Filipa Faleiro,Maria Rita Pegado,Mário S Diniz,Regina Bispo,Marta Pimentel,Rui Rosa,Ana Rita Lopes

doi:10.1093/conphys/cow017

Abstract

Small pelagic fishes are known to respond rapidly to changes in ocean climate. In this study, we evaluate the effects of future environmental warming (+2°C) during the early ontogeny of the European sardine, Sardina pilchardus. Warming reduced the survival of 30-day-old larvae by half. Length at hatching increased with temperature as expected, but no significant effect was observed on the length and growth at 30 days post-hatching. Warming did not significantly affect the thermal tolerance of sardine larvae, even though the mean lethal temperature increased by 1°C. In the warm conditions, sardine larvae showed signs of thermal stress, indicated by a pronounced increase in larval metabolism (Q 10 = 7.9) and a 45% increase in the heat shock response. Lipid peroxidation was not significantly affected by the higher temperature, even though the mean value doubled. Warming did not affect the time larvae spent swimming, but decreased by 36% the frequency of prey attacks. Given the key role of these small pelagics in the trophic dynamics off the Western Iberian upwelling ecosystem, the negative effects of warming on the early stages may have important implications for fish recruitment and ecosystem structure.

Highlights

The importance of small pelagic fishes in marine ecosystems goes far beyond what their size would suggest
In order to understand how sardine early stages may respond to future changes in ocean temperature, we evaluated the impact of warming (+2°C) on the survival, growth, metabolism, thermal tolerance, behaviour, heat shock response and lipid peroxidation in sardine larvae
The distribution and abundance of S. pilchardus is well known to fluctuate with seawater temperature (e.g. Coombs et al, 2006; Planque et al, 2007; Bellido et al, 2008; Alheit et al, 2012; Santos et al, 2013; Montero-Serra et al, 2015), but it remains unclear how higher temperatures affect the biology of this species

Summary

Introduction

The importance of small pelagic fishes in marine ecosystems goes far beyond what their size would suggest. The lower and higher trophic levels contain a higher species richness than intermediate levels, which are dominated by only one or a few small pelagic fish species (Bakun, 1996) These small and planktotrophic fishes play a crucial role in the trophic dynamics of marine ecosystems, either by top-down controlling planktonic organisms or bottom-up controlling predators (Cury et al, 2000). Besides their important ecological role, small pelagic fishes are a valuable component of fisheries all over the world, representing over a third of the global yield of marine fishes and contributing significantly to the economy of many countries (Hunter and Alheit, 1995; Pikitch et al, 2014).

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