Combined effect of pCO2 and temperature levels on the thermal niche in the early benthic ontogeny of a keystone species

Mar 4, 2020The Science of the total environment

Combined effects of carbon dioxide and temperature on the early development temperature range of a key species

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Abstract

Exposure to extreme temperatures significantly affected physiological stress in juvenile Concholepas concholepas as indicated by increased HSP70 transcript levels.

HSP70 transcript levels were significantly higher after exposure to extreme temperatures of 10 °C and 25 °C, indicating physiological stress.
Oxygen consumption rates increased from 10 °C to 20 °C but decreased at 25 °C, regardless of pCO levels.
Juveniles showed similar thermal tolerance under present-day and near-future pCO levels at 20 °C.
Thermal tolerance polygon areas were narrower at 25 °C and broader at 10 °C due to changes in critical thermal limits.
Temperature impacted growth, oxygen consumption, and HSP70 transcription in juveniles, while elevated pCO levels did not affect these at normal temperatures.

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We evaluated the effects of projected, near future ocean acidification (OA) and extreme events of temperature (warming or cooling) on the thermal tolerance of Concholepas concholepas, a coastal benthic keystone species. Three separate trials of an experiment were conducted by exposing juvenile C. concholepas for 1 month to one of two contrasting pCOlevels (~500 and ~1200 μatm). In addition, each pCOlevel was combined with one of four temperature treatments. The control was 15 °C, whilst the other temperatures were 10 °C (Trial 1), 20 °C (Trial 2) and 25 °C (Trial 3). At the end of each trial, we assessed Critical Thermal maximum (CTmax) and minimum (CTmin) via self-righting success, calculated partial thermal tolerance polygons, measured somatic growth, determined transcription of Heat Shock Proteins 70 (HSP70) and measured oxygen consumption rates. Regardless of pCOlevel, HSP70 transcript levels were significantly higher in juveniles after exposure to extreme temperatures (10 °C and 25 °C) indicating physiological stress. Oxygen consumption rates increased with increasing temperature from 10 °C to 20 °C though showed a decrease at 25 °C. This rate was not affected by pCOor the interaction between temperature and pCO. Juveniles exposed to present-day and near future pCOlevels at 20 °C showed similar thermal tolerance polygonal areas; whilst changes in both CTmin and CTmax at 25 °C and 10 °C caused narrower and broader areas, respectively. Temperature affected growth, oxygen consumption and HSP70 transcription in small juvenile C. concholepas. Exposure to elevated pCOdid not affect thermal tolerance, growth or oxygen consumption at temperatures within the thermal range normally experienced by this species in northern Chile (15-20 °C). At elevated pCOconditions, however, exposure to warmer (25 °C) or colder (10 °C) temperatures reduced or increased the thermal area, respectively. This study demonstrates the importance of examining the thermal-tolerance edges to better understand how OA and temperature will combine to physiologically challenge inter-tidal organisms. 2 2 2 2 2 2 2 2

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Combined effect of pCO2 and temperature levels on the thermal niche in the early benthic ontogeny of a keystone species

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