Low NHN and Micheli F (2020), Short- and long-term impacts of variable hypoxi...

ECB-ART-48581

Sci Rep 2020 Feb 14;101:2632. doi: 10.1038/s41598-020-59483-5.

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Short- and long-term impacts of variable hypoxia exposures on kelp forest sea urchins.

Low NHN , Micheli F .

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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 urchin Strongylocentrotus 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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Genes referenced: impact LOC100887844

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	Figure 1. (A) Dissolved oxygen concentrations (mg/L) over time in each treatment. (B) Sea urchin metabolic rates as a proportion of their baseline (±SE). The dashed line indicates baseline (ambient) metabolic rates. Dots (.) and asterisks (*) denote values that were different from the baseline at the α = 0.1 and α = 0.05 significance levels respectively, based on one-sample t-tests.
	Figure 2. Mass-specific kelp grazing rates (g/g/day) of sea urchins in each dissolved oxygen treatment, measured over a three-day experimental period. Error bars represent the standard error of the mean. Letters indicate differences in mass-specific kelp grazing based on Tukey HSD tests.
	Figure 3. Cumulative kelp consumption (g) of sea urchins in ambient dissolved oxygen (DO) conditions, constant exposure to low DO, 3-hour variable exposure to low DO, and 6-hour variable exposure to low DO over the 64-day experiment. Error bars represent the standard error of the mean. Letters indicate differences in mean final cumulative kelp consumption based on Tukey HSD tests.
	Figure 4. Growth, calcification, and reproductive investment of purple sea urchins in each dissolved oxygen treatment. (A) Percentage wet mass growth after 65 days; (B) Length of regrown spines after 30 days; (C) Percentage buoyant mass growth after 65 days; (D) Final gonad index after 65 days. Error bars represent the standard error of the mean and letters indicate differences in mass-specific kelp grazing based on Tukey HSD tests.

References [+] :

Bates, Biologists ignore ocean weather at their peril. 2018, Pubmed