Abstract
AbstractIncreasing water temperatures are predicted around the globe, with high amplitudes of warming in Subarctic and Arctic regions where Atlantic cod (Gadus morhua) populations currently flourish. We reconstructed oxygen isotope and temperature chronologies from Icelandic cod otoliths, one of the largest cod stocks in the world, to determine if cod moved or migrated over the last 100 years to avoid increasing water temperatures. For δ18Ootolith analysis, individual annual growth increments from immature and mature life history stages were micromilled from adult otoliths, which were collected in southern Iceland. Linear mixed-effect models confirmed that stable oxygen isotope time series of immature and mature cod differ significantly between both life stages (p < 0.001). Overall, cod otolith δ18O was significantly correlated with water temperature (sea surface temperature: p < 0.001, temperature at 200 m depth: p < 0.01), indicating that Atlantic cod were exposed to fluctuating water temperatures during the past 100 years and did not move as a response to increasing ocean temperatures. All of the alternate physical factors that were considered for the isotope-based variation in the temperature exposure of Icelandic cod were rejected.
Highlights
Global warming is causing a rise in sea level, decrease in sea ice cover in polar regions, and range shifts across all taxa (e.g. IPCC, 2013)
The d18Ootolith of our samples was significantly correlated with measured water temperatures, suggesting that cod were exposed to water temperature variations over the past century and did not move to avoid it
The mean ambient temperature reconstructed for Icelandic cod is 4.8C, well within physiological tolerances
Summary
Global warming is causing a rise in sea level, decrease in sea ice cover in polar regions, and range shifts across all taxa (e.g. IPCC, 2013). Rising water temperatures will force many taxa of marine aquatic organisms to move to areas outside their current distribution area. Some marine mammals such as the narwhal (Monodon monoceros) or the polar bear (Ursus maritimus) are dependent on sea ice and cannot change their habitat (Simmonds and Isaac, 2007). Rising water temperatures have already led to distributional changes on several different scales in marine ecosystems In the North Sea, cod, anglerfish (Lophius piscatorius), and snake blenny (Ophidion barbatum) showed climate-related latitudinal changes >25 years, but fish can change their depth range rather than their latitudinal distribution [e.g. plaice (Pleuronectes platessa) in the North Sea; Perry et al, 2005]
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