Denise L. Breitburg

Planetary boundaries represent thresholds in major Earth system processes that are sensitive to human activity and control global-scale habitability and stability. These processes are interconnected such that movement of one planetary boundary process can alter the likelihood of crossing other boundaries. Here we argue that the observed deoxygenation of the Earth’s freshwater and marine ecosystems represents an additional planetary boundary process that is critical to the integrity of Earth’s ecological and social systems, and both regulates and responds to ongoing changes in other planetary boundary processes. Research on the rapid and ongoing deoxygenation of Earth’s aquatic habitats indicates that relevant, critical oxygen thresholds are being approached at rates comparable to other planetary boundary processes. Concerted global monitoring, research and policy efforts are needed to address the challenges brought on by rapid deoxygenation, and the expansion of the planetary boundaries framework to include deoxygenation as a boundary helps to focus those efforts.

Climate change is having substantial impacts on organism fitness and ability to deliver critical ecosystem services, but these effects are often examined only in response to current environments. Past exposure to stress can also affect individuals via carryover effects, and whether these effects scale from individuals to influence ecosystem function and services is unknown. We explored within‐generation carryover effects of two coastal climate change stressors—hypoxia and warming—on oyster (Crassostrea virginica) growth and nitrogen bioassimilation, an important ecosystem service. Oysters were exposed to a factorial combination of two temperature and two diel‐cycling dissolved oxygen treatments at 3‐months‐old and again 1 year later. Carryover effects of hypoxia and warming influenced oyster growth and nitrogen storage in complex and context‐dependent ways. When operating, carryover effects of single stressors generally reduced oyster nitrogen bioassimilation and relative investment in tissue versus shell growth, particularly in warm environments, while early life exposure to multiple stressors generally allowed oysters to perform as well as control oysters. When extrapolated to the reef scale, carryover effects decreased nitrogen stored by modeled oyster reefs in most conditions, with reductions as large as 41%, a substantial decline in a critical ecosystem service. In some scenarios, however, carryover effects increased nitrogen storage by modeled oyster reefs, again highlighting the complexity of these effects. Hence, even brief exposure to climate change stressors early in life may have persistent effects on an ecosystem service 1 year later. Our results show for the first time that within‐generation carryover effects on individual phenotypes can impact processes at the ecosystem scale and may therefore be an overlooked factor determining ecosystem service delivery in response to anthropogenic change.

Climate change is having substantial impacts on organism fitness and ability to deliver critical ecosystem services, but these effects are often examined only in response to current environments. Past exposure to stress can also affect individuals via carryover effects, and whether these effects scale from individuals to influence ecosystem function and services is unclear. We explored carryover effects of two coastal climate change stressors – hypoxia and warming – on oyster ( Crassostrea virginica ) growth and nitrogen bioassimilation, an important ecosystem service. Oysters were exposed to a factorial combination of two temperature and two diel-cycling dissolved oxygen treatments at three-months-old and again one year later. Carryover effects of hypoxia and warming influenced oyster growth and nitrogen storage, with early life stress generally reducing nitrogen storage and relative tissue growth, particularly in warm environments. When extrapolated to the reef scale, carryover effects reduced estimated nitrogen storage by a restored oyster reef by as much as 41%, a substantial decline in a critical ecosystem service. Even brief exposure to climate change stressors early in life has persistent, negative effects on an ecosystem service one year later. Carryover effects on individuals impact processes at the ecological scale and must be considered in assessments of and management plans for species and ecosystems threatened by anthropogenic change. Significance Statement: Anthropogenic change threatens organisms’ ability to provide ecosystem services through effects on individual phenotypes. Past experiences with anthropogenic stress can have delayed, persistent impacts on organisms via carryover effects, but how carryover effects scale to influence ecosystem function and services is not yet established. In marine systems, foundation species such as oysters mitigate effects of eutrophication by storing nutrients like nitrogen in their tissue and shell. We show that past exposure to two interacting climate change stressors (hypoxia and warming) reduces nitrogen stored by oysters by as much as 41% one year after initial exposure. Our results reveal carryover effects as a novel pathway through which climate change affects ecosystem processes that should be incorporated into conservation and management plans.

Beneath the waves, oxygen disappears: As plastic waste pollutes the oceans and fish stocks decline, unseen below the surface another problem grows: deoxygenation. Breitburg et al. review the evidence for the downward trajectory of oxygen levels in increasing areas of the open ocean and coastal waters. Rising nutrient loads coupled with climate change—each resulting from human activities—are changing ocean biogeochemistry and increasing oxygen consumption. This results in destabilization of sediments and fundamental shifts in the availability of key nutrients. In the short term, some compensatory effects may result in improvements in local fisheries, such as in cases where stocks are squeezed between the surface and elevated oxygen minimum zones. In the longer term, these conditions are unsustainable and may result in ecosystem collapses, which ultimately will cause societal and economic harm. Science , this issue p. eaam7240

Coastal shoreline hardening is intensifying due to human population growth and sea level rise. Prior studies have emphasized shoreline-hardening effects on faunal abundance and diversity; few have examined effects on faunal biomass and size structure or described effects specific to different functional groups. We evaluated the biomass and size structure of mobile fish and crustacean assemblages within two nearshore zones (waters extending 3 and 16 m from shore) adjacent to natural (native wetland; beach) and hardened (bulkhead; riprap) shorelines. Within 3 m from shore, the total fish/crustacean biomass was greatest at hardened shorelines, driven by greater water depth that facilitated access to planktivore (e.g., bay anchovy) and benthivore-piscivore (e.g., white perch) species. Small-bodied littoral-demersal species (e.g., Fundulus spp.) had greatest biomass at wetlands. By contrast, total biomass was comparable among shoreline types within 16 m from shore, suggesting the effect of shoreline hardening on fish biomass is largely within extreme nearshore areas immediately at the land/water interface. Shoreline type utilization was mediated by body size across all functional groups: small individuals (≤60 mm) were most abundant at wetlands and beaches, while large individuals (>100 mm) were most abundant at hardened shorelines. Taxonomic diversity analysis indicated natural shoreline types had more diverse assemblages, especially within 3 m from shore, although relationships with shoreline type were weak and sensitive to the inclusion/exclusion of crustaceans. Our study illustrates how shoreline hardening effects on fish/crustacean assemblages are mediated by functional group, body size, and distance from shore, with important applications for management.

Acidification research has exploded in recent years, however, experiments testing effects of co‐cycling hypoxia and pH on ecological and physiological processes are rare, despite the pervasiveness and potential importance of co‐varying fluctuations in these parameters. Co‐cycling dissolved oxygen (DO) and pH are difficult to precisely control, as gases used for manipulation influence both parameters. We successfully developed a LabVIEW™‐based system capable of monitoring and controlling co‐varying DO and pH in raw seawater flow‐through aquaria. Using feedback from Oxyguard DO probes and Honeywell ion sensitive field effect transistor Durafet pH sensors, our system controls ratios of nitrogen, oxygen, carbon dioxide, atmospheric air, and CO₂‐stripped air within a total gas flow rate through mass flow controllers, to achieve target co‐cycling DO and pH values in five treatments. Our system performed well in two long‐term experiments investigating effects of diel‐cycling hypoxia and pH on eastern oyster (Crassostrea virginica)feeding, growth, fecundity,Perkinsussp. (Dermo) infection dynamics and immune response. In our 2013 adult oyster experiment, the severe low DO treatment averaged only 0.04 mg L⁻¹higher than the 0.50 mg L⁻¹target, and the moderate hypoxia averaged only 0.05 mg L⁻¹higher than the 1.30 mg L⁻¹target over 48 d of cycles. Mean pH for the hypercapnia plateau was within 0.02 above the 7.00 target. In our 2013 spat experiment, daily minimum DO in the severe and moderate hypoxia treatments were both within 0.06 mg L⁻¹of the 0.50 and 1.3 mg L⁻¹targets, respectively; hypercapnia plateau pH values were within 0.01 of our 7.00 target.

Publisher's PDF.Oceanic and coastal waters are acidifying due to processes dominated in the open ocean by increasing atmospheric CO2 and dominated in estuaries and some coastal waters by nutrient-fueled respiration. The patterns and severity of acidification, as well as its effects, are modified by the host of stressors related to human activities that also influence these habitats. Temperature, deoxygenation, and changes in food webs are particularly important co-stressors because they are pervasive, and both their causes and effects are often mechanistically linked to acidification. Development of a theoretical underpinning to multiple stressor research that considers physiological, ecological, and evolutionary perspectives is needed because testing all combinations of stressors and stressor intensities experimentally is impossible. Nevertheless, use of a wide variety of research approaches is a logical and promising strategy for improving understanding of acidification and its effects. Future research that focuses on spatial and temporal patterns of stressor interactions and on identifying mechanisms by which multiple stressors affect individuals, populations, and ecosystems is critical. It is also necessary to incorporate consideration of multiple stressors into management, mitigation, and adaptation to acidification and to increase public and policy recognition of the importance of addressing acidification in the context of the suite of other stressors with which it potentially interacts.University of Delaware. School of Marine Science and Policy

Diel-cycling hypoxia is widespread in shallow portions of estuaries and lagoons, especially in systems with high nutrient loads resulting from human activities. Far less is known about the effects of this form of hypoxia than deeper-water seasonal or persistent low dissolved oxygen. We examined field patterns of diel-cycling hypoxia and used field and laboratory experiments to test its effects on acquisition and progression of Perkinsus marinus infections in the eastern oyster, Crassostrea virginica, as well as on oyster growth and filtration. P. marinus infections cause the disease known as Dermo, have been responsible for declines in oyster populations, and have limited success of oyster restoration efforts. The severity of diel-cycling hypoxia varied among shallow monitored sites in Chesapeake Bay, and average daily minimum dissolved oxygen was positively correlated with average daily minimum pH. In both field and laboratory experiments, diel-cycling hypoxia increased acquisition and progression of infections, with stronger results found for younger (1-year-old) than older (2-3-year-old) oysters, and more pronounced effects on both infections and growth found in the field than in the laboratory. Filtration by oysters was reduced during brief periods of exposure to severe hypoxia. This should have reduced exposure to waterborne P. marinus, and contributed to the negative relationship found between hypoxia frequency and oyster growth. Negative effects of hypoxia on the host immune response is, therefore, the likely mechanism leading to elevated infections in oysters exposed to hypoxia relative to control treatments. Because there is considerable spatial variation in the frequency and severity of hypoxia, diel-cycling hypoxia may contribute to landscape-level spatial variation in disease dynamics within and among estuarine systems.