Posts Tagged 'oxygen'

Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth

Highlights

• Elevated CO2 and reduced dissolved oxygen have opposite effects on otolith (earstone) development in juvenile copper and blue rockfish.

• Increased CO2 levels resulted in otoliths being larger in area for a relative fish body size in blue rockfish.

• Reduced dissolved oxygen levels results in otoliths being smaller in area for a relative fish body size in both species.

Abstract

Climate change is predicted to alter ocean chemistry through warming temperatures, increases in CO2 (i.e., ocean acidification), and reductions in dissolved oxygen (DO) (i.e., hypoxia). Past research has shown that early life stages of marine fishes are sensitive to all three stressors, but with sometimes different directions of response. In this study, we examined the separate effects of ocean acidification and hypoxia on otolith growth in two species of juvenile rockfish (copper rockfish, Sebastes caurinus, and blue rockfish, Sebastes mystinus). Fishes were collected at settlement stage from kelp forests on the central California coast and reared in the laboratory for up to 6 months in 4 separate pH treatments (pH = 7.3, 7.6, 7.8, and a control of 8.0), simulating the effects of ocean acidification through the addition of CO2, and 4 separate dissolved oxygen treatments (DO = 2.2, 4.1, 6.0, and a control of 8.7 mg/L), simulating the effects of hypoxia. For both species, otoliths were smaller for a given fish length in response to hypoxia but were larger (trend was non-significant for copper rockfish) in response to elevated CO2. The results suggest that otolith growth may respond differently to ocean acidification and hypoxia for some species, which has implications for sensory development, ecological performance, and interpretations of the permanent record of fish growth in hard parts such as otoliths.

Continue reading ‘Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth’

Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga

Ecological impact of global change is generated by multiple synchronous or asynchronous drivers which interact with each other and with intraspecific variability of sensitivities. In three near-natural experiments, we explored response correlations of full-sibling germling families of the seaweed Fucus vesiculosus towards four global change drivers: elevated CO2 (ocean acidification, OA), ocean warming (OW), combined OA and warming (OAW), nutrient enrichment and hypoxic upwelling. Among families, performance responses to OA and OW as well as to OAW and nutrient enrichment correlated positively whereas performance responses to OAW and hypoxia anti-correlated. This indicates (i) that families robust to one of the three drivers (OA, OW, nutrients) will also not suffer from the two other shifts, and vice versa and (ii) families benefitting from OAW will more easily succumb to hypoxia. Our results may imply that selection under either OA, OW or eutrophication would enhance performance under the other two drivers but simultaneously render the population more susceptible to hypoxia. We conclude that intraspecific response correlations have a high potential to boost or hinder adaptation to multifactorial global change scenarios.

Continue reading ‘Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga’

Stress across life stages: impacts, responses and consequences for marine organisms

Highlights

• The published data were analysed to assess carry-over effects on marine organisms.

• The capacity of larvae to recover from early starvation and hypoxia was tested.

• Food limitation is the main driver of negative carry-over effects on juvenile growth.

• Larvae can recover from the early stress without negative imprints as juveniles.

• Carry-over effects depend on the duration of stress relative to larval period.

Abstract

Population dynamics of marine organisms are strongly driven by their survival in early life stages. As life stages are tightly linked, environmental stress experienced by organisms in the early life stage can worsen their performance in the subsequent life stage (i.e. carry-over effect). However, stressful events can be ephemeral and hence organisms may be able to counter the harmful effects of transient stress. Here, we analysed the published data to examine the relative strength of carry-over effects on the juvenile growth of marine organisms, caused by different stressors (hypoxia, salinity, starvation, ocean acidification and stress-induced delayed metamorphosis) experienced in their larval stage. Based on 31 relevant published studies, we revealed that food limitation had the greatest negative carry-over effect on juvenile growth. In the laboratory, we tested the effects of short-term early starvation and hypoxia on the larval growth and development of a model organism, polychaete Hydroides elegans, and assessed whether the larvae can accommodate the early stress to maintain their performance as juveniles (settlement and juvenile growth). Results showed that early starvation for 3 days (∼50% of normal larval period) retarded larval growth and development, leading to subsequent reduced settlement rate and juvenile growth. When the starvation period decreased to 1 day, however, the larvae could recover from early starvation through compensatory growth and performed normal as juveniles (c.f. control). Early exposure to hypoxia did not affect larval growth (body length) and juvenile growth (tube length), but caused malformation of larvae and reduced settlement rate. We conclude that the adverse effects of transient stress can be carried across life stages, but depend on the duration of stressful events relative to larval period. As carry-over effects are primarily driven by energy acquisition, how food availability varies over time and space is fundamental to the population dynamics of marine organisms.

Continue reading ‘Stress across life stages: impacts, responses and consequences for marine organisms’

The dynamics and impact of ocean acidification and hypoxia: insights from sustained investigations in the Northern California Current Large Marine Ecosystem

Coastal upwelling ecosystems around the world are defined by wind-generated currents that bring deep, nutrient-rich waters to the surface ocean where they fuel exceptionally productive food webs. These ecosystems are also now understood to share a common vulnerability to ocean acidification and hypoxia (OAH). In the California Current Large Marine Ecosystem (CCLME), reports of marine life die-offs by fishers and resource managers triggered research that led to an understanding of the risks posed by hypoxia. Similarly, unprecedented losses from shellfish hatcheries led to novel insights into the coastal expression of ocean acidification. Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) scientists and other researchers in the CCLME responded to the rise of OAH with new ocean observations and experiments. This work revealed insights into the expression of OAH as coupled environmental stressors, their temporal and spatial variability, and impacts on species, ecological communities, and fisheries. Sustained investigations also deepened the understanding of connections between climate change and the intensification of hypoxia, and are beginning to inform the ecological and eco-evolutionary processes that can structure responses to the progression of ocean acidification and other pathways of global change. Moreover, because the severity of the die-offs and hatchery failures and the subsequent scientific understanding combined to galvanize public attention, these scientific advances have fostered policy advances. Across the CCLME, policymakers are now translating the evolving scientific understanding of OAH into new management actions.

Continue reading ‘The dynamics and impact of ocean acidification and hypoxia: insights from sustained investigations in the Northern California Current Large Marine Ecosystem’

Ocean acidification and hypoxia alter organic carbon fluxes in marine soft sediments

Anthropogenic stressors can alter the structure and functioning of infaunal communities, which are key drivers of the carbon cycle in marine soft sediments. Nonetheless, the compounded effects of anthropogenic stressors on carbon fluxes in soft benthic systems remain largely unknown. Here, we investigated the cumulative effects of ocean acidification (OA) and hypoxia on the organic carbon fate in marine sediments, through a mesocosm experiment. Isotopically labelled macroalgal detritus (13C) was used as a tracer to assess carbon incorporation in faunal tissue and in sediments under different experimental conditions. In addition, labelled macroalgae (13C), previously exposed to elevated CO2, were also used to assess the organic carbon uptake by fauna and sediments, when both sources and consumers were exposed to elevated CO2. At elevated CO2, infauna increased the uptake of carbon, likely as compensatory response to the higher energetic costs faced under adverse environmental conditions. By contrast, there was no increase in carbon uptake by fauna exposed to both stressors in combination, indicating that even a short‐term hypoxic event may weaken the ability of marine invertebrates to withstand elevated CO2 conditions. In addition, both hypoxia and elevated CO2 increased organic carbon burial in the sediment, potentially affecting sediment biogeochemical processes. Since hypoxia and OA are predicted to increase in the face of climate change, our results suggest that local reduction of hypoxic events may mitigate the impacts of global climate change on marine soft‐sediment systems.

Continue reading ‘Ocean acidification and hypoxia alter organic carbon fluxes in marine soft sediments’

Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)

Highlights

  • Marine fishes will be exposed to multiple stressors under climate change.
  • Hypoxia and high pCO2 are both expected to cause shifts in energy metabolism.
  • No signs of energetic shifts were observed at transcriptomic or enzymatic levels.
  • Multiple stressor transcriptomes are not predictable based on responses to single stressors.
  • Blue rockfish may be relatively tolerant to intensified upwelling conditions.

Abstract

Global climate change is predicted to increase the co-occurrence of high pCO2 and hypoxia in upwelling zones worldwide. Yet, few studies have examined the effects of these stressors on economically and ecologically important fishes. Here, we investigated short-term responses of juvenile blue rockfish (Sebastes mystinus) to independent and combined high pCO2 and hypoxia at the molecular level, using changes in gene expression and metabolic enzymatic activity to investigate potential shifts in energy metabolism. Fish were experimentally exposed to conditions associated with intensified upwelling under climate change: high pCO2 (1200 μatm, pH~7.6), hypoxia (4.0 mg O2/L), and a combined high pCO2/hypoxia treatment for 12 h, 24 h or two weeks. Muscle transcriptome profiles varied significantly among the three treatments, with limited overlap among genes responsive to both the single and combined stressors. Under elevated pCO2, blue rockfish increased expression of genes encoding proteins involved in the electron transport chain and muscle contraction. Under hypoxia, blue rockfish up-regulated genes involved in oxygen and ion transport and down-regulated transcriptional machinery. Under combined high pCO2 and hypoxia, blue rockfish induced a unique set of ionoregulatory and hypoxia-responsive genes not expressed under the single stressors. Thus, high pCO2 and hypoxia exposure appears to induce a non-additive transcriptomic response that cannot be predicted from single stressor exposures alone, further highlighting the need for multiple stressor studies at the molecular level. Overall, lack of a major shift in cellular energetics indicates that blue rockfish may be relatively resistant to intensified upwelling conditions in the short term.

Continue reading ‘Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)’

Hypoxia aggravates the effects of ocean acidification on the physiological energetics of the blue mussel Mytilus edulis

Highlights

• Combined effects of ocean acidification and hypoxia are investigated in mussels.

• Physiological activities of mussels are inhibited by low pH and hypoxia.

• OA and hypoxia exert additive effects on the physiological metabolism of mussels.

Abstract

Apart from ocean acidification, hypoxia is another stressor to marine organisms, especially those in coastal waters. Their interactive effects of elevated CO2 and hypoxia on the physiological energetics in mussel Mytilus edulis were evaluated. Mussels were exposed to three pH levels (8.1, 7.7, 7.3) at two dissolved oxygen levels (6 and 2 mg L−1) and clearance rate, absorption efficiency, respiration rate, excretion rate, scope for growth and O: N ratio were measured during a14-day exposure. After exposure, all parameters (except excretion rate) were significantly reduced under low pH and hypoxic conditions, whereas excretion rate was significantly increased. Additive effects of low pH and hypoxia were evident for all parameters and low pH appeared to elicit a stronger effect than hypoxia (2.0 mg L−1). Overall, hypoxia can aggravate the effects of acidification on the physiological energetics of mussels, and their populations may be diminished by these stressors.

Continue reading ‘Hypoxia aggravates the effects of ocean acidification on the physiological energetics of the blue mussel Mytilus edulis’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book