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 for M. francicanus over both acute and chronic timescales. Promartynia pulligo exhibited 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 for M. 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.

The Diversity and Functional Capacity of Microbes Associated with Coastal Macrophytes

“…At larger scales, canopy forming kelps elevate daytime dissolved oxygen (DO) levels in seawater within kelp forest stands compared to the surrounding water column ( 17 ). At night, however, the DO levels in these kelp forests may drop to between 2 to 10 mg L −1 ( 18 ). Similarly, diel fluctuations that range an order of magnitude have been measured in rocky shore tidepools that include the surfgrass Phyllospadix scouleri ( 19 , 20 ).…”

Upwelling‐level acidification and pH/pCO2 variability moderate effects of ocean acidification on brain gene expression in the temperate surfperch, Embiotoca jacksoni

“…The contrast of our results may reflect the transgenerational and evolutionary exposure history of E. jacksoni populations to naturally acidic environments. While A. polyacanthus on coral reefs may experience diurnal p CO 2 fluctuations on the scale of ±50–150 μatm (Schunter et al, 2021 and references therein), E. jacksoni in upwelling regions are likely to regularly experience prolonged increases in p CO 2 (days to weeks) from as low as ~300 to >1000 μatm (Chavez et al, 2018; Donham et al, 2022). Those living in estuaries can experience even greater shifts in carbonate chemistry over even shorter timescales (Duarte et al, 2013; Hofmann et al, 2011).…”

Population-specific vulnerability to ocean change in a multistressor environment

“…To measure the standard metabolic rates of individuals, we followed methods outlined by Donham et al. ( 30 ). Briefly, we placed individual sea urchins into polycarbonate respirometry chambers (either ~100 or ~230 ml, depending on the size of the urchin) with seawater from their respective treatment.…”

“…Forty-eight hours before grazing assays, we removed kelp from sea urchin cages and starved individuals to reduce the potential effects of digestive status on metabolism measurements. To measure the standard metabolic rates of individuals, we followed methods outlined by Donham et al (30). Briefly, we placed individual sea urchins into polycarbonate respirometry chambers (either ~100 or ~230 ml, depending on the size of the urchin) with seawater from their respective treatment.…”

“…Therefore, predicted changes in the mean due to climate change and OA (increases in temperature but decreases in pH and DO) will also alter their covariance. The covariance between temperature, pH, and DO is especially strong during upwelling season ( 30 ). Therefore, regions within the CCS that are more influenced by upwelling are also likely to experience greater deviations in the covariance structure of these three environmental drivers in response to global change compared to regions where environmental conditions are less influenced by upwelling.…”