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Abstract Climate change is altering the intensity and variability of environmental stress that organisms and ecosystems experience, but effects of changing stress regimes are not well understood. We examined impacts of constant and variable sublethal hypoxia exposures on multiple biological processes in the sea urchinStrongylocentrotus purpuratus, a key grazer in California Current kelp forests, which experience high variability in physical conditions. We quantified metabolic rates, grazing, growth, calcification, spine regeneration, and gonad production under constant, 3-hour variable, and 6-hour variable exposures to sublethal hypoxia, and compared responses for each hypoxia regime to normoxic conditions. Sea urchins in constant hypoxia maintained baseline metabolic rates, but had lower grazing, gonad development, and calcification rates than those in ambient conditions. The sublethal impacts of variable hypoxia differed among biological processes. Spine regrowth was reduced under all hypoxia treatments, calcification rates under variable hypoxia were intermediate between normoxia and constant hypoxia, and gonad production correlated negatively with continuous time under hypoxia. Therefore, exposure variability can differentially modulate the impacts of sublethal hypoxia, and may impact sea urchin populations and ecosystems via reduced feeding and reproduction. Addressing realistic, multifaceted stressor exposures and multiple biological responses is crucial for understanding climate change impacts on species and ecosystems.
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Coupled changes in pH, temperature, and dissolved oxygen impact the physiology and ecology of herbivorous kelp forest grazers
Abstract Understanding species’ responses to upwelling may be especially important in light of ongoing environmental change. Upwelling frequency and intensity are expected to increase in the future, while ocean acidification and deoxygenation are expected to decrease the pH and dissolved oxygen (DO) of upwelled waters. However, the acute effects of a single upwelling event and the integrated effects of multiple upwelling events on marine organisms are poorly understood. Here, we use in situ measurements of pH, temperature, and DO to characterize the covariance of environmental conditions within upwelling‐dominated kelp forest ecosystems. We then test the effects of acute (0–3 days) and chronic (1–3 months) upwelling on the performance of two species of kelp forest grazers, the echinoderm,Mesocentrotus franciscanus, and the gastropod,Promartynia pulligo. We exposed organisms to static conditions in a regression design to determine the shape of the relationship between upwelling and performance and provide insights into the potential effects in a variable environment. We found that respiration, grazing, growth, and net calcification decline linearly with increasing upwelling intensity forM.francicanusover both acute and chronic timescales.Promartynia pulligoexhibited decreased respiration, grazing, and net calcification with increased upwelling intensity after chronic exposure, but we did not detect an effect over acute timescales or on growth after chronic exposure. Given the highly correlated nature of pH, temperature, and DO in the California Current, our results suggest the relationship between upwelling intensity and growth in the 3‐month trial could potentially be used to estimate growth integrated over long‐term dynamic oceanographic conditions forM.franciscanus. Together, these results indicate current exposure to upwelling may reduce species performance and predicted future increases in upwelling frequency and intensity could affect ecosystem function by modifying the ecological roles of key species.
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- Award ID(s):
- 1524377
- PAR ID:
- 10415365
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 28
- Issue:
- 9
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 3023-3039
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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