skip to main content


Title: 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.

 
more » « less
Award ID(s):
1524377
NSF-PAR ID:
10415365
Author(s) / Creator(s):
 ;  ;  ;  
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
More Like this
  1. 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.

     
    more » « less
  2. Abstract

    In an era of global change, the fate and form of reef habitats will depend on shifting assemblages of organisms and their responses to multiple stressors. Multiphyletic assemblages of calcifying and bioeroding species contribute to a dynamic balance between constructive and erosive processes, and reef‐framework growth occurs only when calcium‐carbonate deposition exceeds erosion. Each contributing species exhibits a unique combination of environmental sensitivities, trophic needs, and competitive abilities, making the net outcome of their habitat‐altering behavior difficult to predict. In this study, standardized blocks of clean, massivePoriteswere placed at six reef sites in the eastern tropical Pacific, in the strongly and more‐weakly upwelling Gulfs of Panamá (GoP) and Chiriquí (GoC), respectively. Sites were chosen to characterize the unique thermal and carbonate‐chemistry conditions of each gulf. Satellite products were used to examine differences in sea‐surface productivity, and surveys were conducted to quantify the abundance of important grazing taxa. After two years in situ, thePoritesblocks were collected and scanned using high‐resolution computed tomography to volumetrically quantify both endolithic and epilithic habitat alteration. Scan‐volumes were further classified into functional groups according to morphology to quantify external bioerosion by fish and sea urchins, as well as the calcifying and bioeroding activity of crustose coralline algae, scleractinian corals, mollusks, annelids, and barnacles. The GoP, which has higher productivity, cooler temperatures, and periodically lower pH conditions, had higher rates of macroboring, but also higher rates of calcification. These unexpectedly higher rates of calcification in the GoP were a result of high recruitment of suspension‐feeding taxa, particularly barnacles and vermiform fauna that have poor reef‐forming potential. External bioerosion by grazers was the dominant process influencing these dead coral substrates across both gulfs, contributing to higher rates of net erosion in the GoC and underscoring the important roles that urchins and fish play in not just removing algae on reefs, but also eroding reef habitat. Ultimately these findings reveal that the trophic requirements of habitat‐altering taxa are closely tied to reef‐framework stability, and that environmental conditions conducive to carbonate precipitation are not necessarily those that will lead to habitat persistence.

     
    more » « less
  3. Upwelling provides high amounts of nutrients that support primary production in coastal habitats, including giant kelp Macrocystis pyrifera forests. Growth and recruitment of kelp forests are controlled by environmental conditions, including temperature, nutrient availability, and storms, as well as biotic interactions. However, our understanding of juvenile persistence in the field is extremely limited, particularly the effects of grazing on the survival of early kelp stages and how environmental variability associated with upwelling dynamics may modulate grazing effects. We quantified herbivore impacts on juvenile M. pyrifera by deploying thirteen 24 h caging experiments approximately every 2 wk throughout the upwelling season in a giant kelp forest in Monterey Bay, CA, USA. Experiments spanned a range of natural environmental variation in oxygen, pH, and temperature, conditions known to affect grazer physiology and that are projected to become more extreme under global climate change. Overall, the herbivore community had a large effect on kelp survival, with 68.5% of juvenile kelp removed on average across experiments. Grazing increased throughout the season, which was most strongly correlated with decreasing monthly oxygen variance and weakly correlated with decreasing monthly pH variance and increasing temperature. This suggests that large swings in oxygen during peak kelp recruitment in spring may provide a temporal refuge from grazing, allowing kelp to reach larger sizes by late summer and fall when upwelling has relaxed. This study highlights the potential of current environmental variability, and its predicted increase under future scenarios, to mediate species interactions and habitat persistence. 
    more » « less
  4. Griffen, Blaine D. (Ed.)
    Ocean acidification (OA) represents a serious challenge to marine ecosystems. Laboratory studies addressing OA indicate broadly negative effects for marine organisms, particularly those relying on calcification processes. Growing evidence also suggests OA combined with other environmental stressors may be even more deleterious. Scaling these laboratory studies to ecological performance in the field, where environmental heterogeneity may mediate responses, is a critical next step toward understanding OA impacts on natural communities. We leveraged an upwelling-driven pH mosaic along the California Current System to deconstruct the relative influences of pH, ocean temperature, and food availability on seasonal growth, condition and shell thickness of the ecologically dominant intertidal mussel Mytilus californianus. In 2011 and 2012, ecological performance of adult mussels from local and commonly sourced populations was measured at 8 rocky intertidal sites between central Oregon and southern California. Sites coincided with a large-scale network of intertidal pH sensors, allowing comparisons among pH and other environmental stressors. Adult California mussel growth and size varied latitudinally among sites and inter-annually, and mean shell thickness index and shell weight growth were reduced with low pH. Surprisingly, shell length growth and the ratio of tissue to shell weight were enhanced, not diminished as expected, by low pH. In contrast, and as expected, shell weight growth and shell thickness were both diminished by low pH, consistent with the idea that OA exposure can compromise shell-dependent defenses against predators or wave forces. We also found that adult mussel shell weight growth and relative tissue mass were negatively associated with increased pH variability. Including local pH conditions with previously documented influences of ocean temperature, food availability, aerial exposure, and origin site enhanced the explanatory power of models describing observed performance differences. Responses of local mussel populations differed from those of a common source population suggesting mussel performance partially depended on genetic or persistent phenotypic differences. In light of prior research showing deleterious effects of low pH on larval mussels, our results suggest a life history transition leading to greater resilience in at least some performance metrics to ocean acidification by adult California mussels. Our data also demonstrate “hot” (more extreme) and “cold” (less extreme) spots in both mussel responses and environmental conditions, a pattern that may enable mitigation approaches in response to future changes in climate. 
    more » « less
  5. ABSTRACT

    In upwelling systems, fluctuations in seawater pH, dissolved oxygen (DO), and temperature can expose species to extremes that differ greatly from the mean conditions. Understanding the nature of this exposure to extremes, including how exposure to low pH, low DO concentrations, and temperature varies spatiotemporally and in the context of other drivers, is critical for informing global change biology. Here, we use a 4‐yr time series of coupled pH, DO, and temperature observations at six nearshore kelp forest sites spanning the coast of California to characterize the variability and covariance among these drivers. We further compare observed properties to those derived from a high‐resolution coupled physical‐biogeochemical simulation for the central California current system. We find the intensity, duration, and severity of exposure to extreme conditions beyond heuristic, biologically relevant pHT(< 7.7), and DO (< 4.6 mg L−1) values were greatest at sites with strong upwelling. In contrast, sites with relatively weaker upwelling had little exposure to pH or DO conditions below these heuristic values but had higher and more variable temperature. The covariance between pH, DO, and temperature was highest in sites with strong upwelling and weakest in sites with limited upwelling. These relationships among pH, DO, and temperature at the observation locations were mirrored in the model, and model output highlighted geographic differences in exposure regimes across the California marine protected area network. Together, these results provide important insight into the conditions marine ecosystems are exposed to relevant to studies of global change biology.

     
    more » « less