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6 Recovery of Marine Ecosystems
Pages 147-180

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From page 147...
... Although the fraction of biomass carbon in the oceans is relatively small compared to that of terrestrial systems, the role of animals in biogeochemical cycles and ecosystem structure has garnered attention, especially in light of the widespread impact of human activities on the state of the oceans and the co-benefits of ecosystem recovery approaches. At the same time, studies of kelp and other macroalgae such as Sargassum, benthic algae, and phytoplankton, have increased our understanding of their potential role in the carbon cycle.
From page 148...
... and sequestration in the oceans, though considerable uncertainties remain, including the role of marine animals in nutrient cycles, the global areal extent of macroalgal and other ecosystems, and the fraction of carbon that is stored or sequestered during many of these ecological processes. See Section 1.4 for discussion of the ocean carbon cycle and the biological pump.
From page 149...
... The preindustrial ocean carbon cycle is thought to have been in approximate steady state, with the biological uptake and downward export of surface CO2 largely balanced by the return of respired CO2 from the deep sea by the physical circulation. Despite the large role of marine systems in the carbon cycle, our understanding of changes or perturbation in ocean CO2 storage from past degradation is not well constrained, and our knowledge of the effects on ocean C storage by restoring and protecting marine organisms, ecological functions, and ecosystems is still emerging.
From page 150...
... Although ecological processes have been well studied in terrestrial and coastal systems, the role of large marine animals and other organisms in the carbon cycle is still relatively new. One compelling question is whether animals and macroalgae have functional impacts that are disproportionate to their biomass, much as mat-forming mosses and lichens play important regulatory roles in the water cycle and inhibit microbial decomposition in some land ecosystems (Smith et al., 2015)
From page 151...
... TABLE 6.1  Selected Studies of Carbon Stored or Sequestered in Existing or Restored Ecosystems Mechanism System Region C Stored or Sequestered Reference Macroalgae flux to detritus Macroalgal–sediment systems UK 0.70 Tg/yr Queirós et al., 2019 Coralline algae growth and deposits C storage by coralline algae and the beds Global 1.6 × Gt C/yr van der Heijden and Kamenos, they create 2015 Potential C sequestered by global Export of C to the deep sea and burial in Global 173 Tg C/yr Krause-Jensen and Duarte, macroalgae coastal sediments 2016 Global ocean C export Biological pump, export of biogenic Global ~6 Pg C/yr Siegel et al., 2014 particles from surface waters to stratified interior Diel vertical migration of fish and Global C fluxes and sequestration by fish Global 5.2 Pg C/yr Pinti et al., 2021 other metazoans and metazoans due to respiration, fecal pellets, and deadfalls Gelatinous zooplankton C flows Sinking of jelly-falls and fecal matter Global 1.6–5.2 Pg C/yr Luo et al., 2020 below 100 meters Fish-based contributions to ocean Passive and active flux from fish feces Global 1.5 ± 1.2 Pg C/yr Saba et al., 2021 C flux and migration Recovery of marine vertebrates and Role of vertebrates in the ocean C cycle, Global No total provided Martin et al., 2021 increase of wild biomass including living biomass, deep-sea carcasses, and nutrient cycling Baleen whale biomass and carcasses Storage of C in living whales and Global 0.0089 Gt C/yr, with potential for Pershing et al., 2010 sequestration of C in deep-sea whale significant increase in restored carcasses populations Sea otter and kelp forest trophic Increase in C storage by kelp forests via Northwest North America 4.4–8.7 Tg C total stored Wilmers et al., 2012 cascade sea otter suppression of herbivorous sea urchins 151
From page 152...
... 152 FIGURE 6.2  Major components of the North American carbon cycle. North American coastal oceans, excluding tidal wetlands and estuaries, have a net uptake of 160 Tg C/yr.
From page 153...
... Proposed restoration techniques include afforestation through seeding of macroalgae; the reversal of trophic cascades through the protection of sea otters and other predators; and exclusion methods such as flexible fencing to reduce sea urchin densities (Sharma et al., 2021)
From page 154...
... The calcification process also reduces seawater alkalinity and increases the partial pressure of CO2, reducing the CDR efficacy of calcifying algae. Animals and the Carbon Cycle It has been suggested that conserving and restoring large marine vertebrates and other animals could provide an ecologically sound alternative to more intensive ocean CDR schemes such as iron
From page 155...
... (It does not, however, include echinoderms, one of the most diverse groups of marine animals, and is thus likely an underestimate.) Although we could not find total estimates for marine mammals, marine arthropods comprise about 1.0 Gt C, and fish (freshwater and marine)
From page 156...
... 156 A RESEARCH STRATEGY FOR OCEAN-BASED CARBON DIOXIDE REMOVAL AND SEQUESTRATION FIGURE 6.5  Animal influence on the marine carbon cycle.
From page 157...
... The recovery of historic numbers of marine animals presents an opportunity in terms of biomass, deadfall carbon (see below) , and the restoration of zoogeochemical pathways in the carbon cycle (Schmitz et al., 2018)
From page 158...
... assumed that about 75 percent of the total iron defecated by sperm whales persists in the photic zone, with iron in the beaks of cephalopod prey sinking. This nutrient contribution can enhance new production, increasing net uptake of CO2 from the atmosphere and C export to the deep ocean, though the amount of carbon that is stored, sequestered, or released back into the surface waters remains an area of active debate (for a review of marine vertebrates in the carbon cycle, see Martin et al., 2021; Roman et al., 2021)
From page 159...
... A variety of measures, including reduction of direct and indirect take, expansion of protected areas, and improved enforcement have helped many of these species, and dedicated efforts have the potential to restore the diversity of marine life. Although the overriding theme of this chapter is CDR in the ocean, it would be counterproductive to ignore the role of marine conservation efforts to protect current stores and flows in the carbon cycle.
From page 160...
... Protected areas can also play direct and indirect roles in the many processes discussed in this chapter: promoting the storage of carbon in biomass and carcasses, protecting the seafloor from trawling and mining, protecting and restoring food webs and reversing human-induced trophic cascades, and reducing the pressures of overharvesting. The push to protect more of the oceans was adopted by the IUCN World Conservation Congress in 2016, calling for 30 percent protection by 2030.
From page 161...
... Methods can include the control of herbivores, such as sea urchins (see Reversing Trophic Cascades and Restoring Food Webs below) and the seeding of macroalgae, including techniques such as "green gravel," small rocks seeded with kelp (Fredriksen et al., 2020)
From page 162...
... . Several new studies have estimated the potential role of rebuilding fish populations in the ocean carbon cycle.
From page 163...
... The restoration of large marine organisms, through fisheries management and mitigation, MPAs, pollution reduction, and other protective policies, can result in increased biomass, deadfall carbon, and nutrient transfer and subsidies. Reversing Trophic Cascades and Restoring Food Webs Animals perform a complex set of trophic and nontrophic interactions that can cascade through food webs and affect carbon processes (e.g., Schmitz et al., 2018)
From page 164...
... The production of CH4 or N2O, or the release of CO2, through respiration should also be accounted for. Additionality Restoring marine ecosystems offers two clear and overlapping benefits: reducing biodiversity loss and restoring the role of marine organisms in the carbon cycle.
From page 165...
... 2001) Whale pump Blue whale (Balaenoptera Southern Ocean 1.3 × 108 t C/yr 2.8 × 106 t C/yr (5.2 × 103, Stored Lavery et al., 2014 musculus)
From page 166...
... All of the remote technologies and data products could be made available for long-term, site-specific ecosystem health monitoring of deep-ocean and seamount MPAs. Regional-scale monitoring Management of other deep-ocean ecosystems requires monitoring of regional-scale threats, such as marine heat waves and ocean deoxygenation, in addition to sitespecific monitoring.
From page 167...
... provide a historic framework for understanding long-term ocean change in areas where these surveys take place. Marine mammal activity in remote protected areas Cabled and autonomous mooring networks can deliver marine mammal monitoring solutions, using underwater hydrophone systems that record whale sounds and ship noise, and AIS data that track vessel movements with a focus on data products that inform long-term management by reporting on monthly and annual levels of marine mammal and large vessel activity in MPAs.
From page 168...
... 6.4 SCALABILITY It is well accepted that oceanic biological processes are an important component in the global carbon cycle (Table 6.1)
From page 169...
... As C emissions approach net zero, a diverse portfolio of marine conservation efforts may have the potential to contribute to global CDR approaches. (See the section on Durability for further discussion of temporal aspects of C sequestration under current and future scenarios.)
From page 170...
... Co-benefits Unlike some of the other ocean-based approaches considered in this report, there are considerable co-benefits in restoring ocean ecosystems, including biodiversity conservation and the restoration of many ecological functions and ecosystem services damaged by human activities such as pollution and overfishing. The recovery of kelp forests, for example, has C, biodiversity, and fisheries benefits (Duarte et al., 2020)
From page 171...
... Energy As is true with costs, under most of the scenarios presented here, the energy required for research activities would be restricted to measuring and monitoring CDR associated with ecosystem and species recovery. These studies would likely be focused on research cruises and equipment necessary to measure marine biogeochemistry and changes in the carbon cycle.
From page 172...
... similarly recognizes that certain "marine mammals are, or may be, in danger of extinction or depletion as a result of man's activi ties" (16 U.S.C.
From page 173...
... For each of these systems, there is a need for research to help understand historical baselines in the context of the carbon cycle, past habitat degradation and organism losses due to human activities, and the potential changes to the characteristics of these systems as a result of climate perturbation and ocean acidification. It would be helpful to estimate the current and historical contribution of different species across the entire size spectrum in terms of annual C flux.
From page 174...
... Kelp forest storage (low, medium, high) restoration, marine protected areas, fisheries management, and restoring marine vertebrate carbon are promising tools.
From page 175...
... By quantifying the human perturbations of C flux in the ocean, we can estimate the potential role of a restored ocean in the carbon cycle (see, e.g., Regnier et al., 2013)
From page 176...
... Social science research can help us understand the institutions, policies, and cultural practices that lead to community support and engagement in marine ecosystem recovery. It can also help determine why efforts sometimes fail and what can make them successful.
From page 177...
... Marine Animals and Carbon Dioxide Removal Given the many uncertainties surrounding CDR and marine animals, quantifying the direct and indirect roles of marine fauna in the carbon cycle is a priority for further research (Stafford et al., 2021)
From page 178...
... Nutrient Cycling The role of iron and nitrogen in the ocean carbon cycle has been well established, yet much of the focus on nutrient fertilization has been on open-ocean iron addition experiments and a few macronutrient (nitrogen and phosphorus) studies or schemes (see Chapter 3)
From page 179...
... Although the CDR potential of ecosystem recovery in the oceans is relatively small in comparison to present greenhouse gas emissions, this is perhaps more a reflection of the magnitude of current global emissions than a diminished role in the seas. As emission rates come down, ocean CDR could rise in importance.
From page 180...
... 2050 6.3 Macroalgae: Carbon measurements, Improve our understanding of the fate of macroalgal carbon, the Low 5 10 global range, and levers of protection range of different species and habitats, and the socioeconomic levers and costs of restoring kelp and other macroalgal habitats 6.4 Benthic communities: disturbance and Improve our understanding of the impacts of human disturbance on Low 5 5 restoration benthic communities and the potential rate of change under different protection scenarios 6.5 Marine animals and CDR Carbon interactions and outcomes have been estimated for only a Low 5 10 few marine species. Efforts will improve our understanding of the direct and indirect impacts of marine animals on CDR, including biomass, deadfall carbon, nutrient transfer, and trophic cascades 6.6 Animal nutrient-cycling Test of models of movement of iron (vertical)


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