Ocean conservation boosts climate change mitigation and adaptation

Abstract

Marine protected areas (MPAs) are increasingly being promoted as an ocean-based climate solution. However, such claims remain controversial because of the diffuse and poorly synthesized literature on climate benefits of MPAs. To address this knowledge gap, we conducted a systematic literature review of 22,403 publications spanning 241 MPAs and analyzed these across 16 ecological and social pathways through which MPAs could contribute to climate change mitigation and adaptation. Our meta-analysis demonstrates that marine conservation can significantly enhance carbon sequestration, coastal protection, biodiversity, and the reproductive capacity of marine organisms as well as fishers’ catch and income. Most of these benefits are only achieved in fully or highly protected areas and increase with MPA age. Although MPAs alone cannot offset all climate change impacts, they are a useful tool for climate change mitigation and adaptation of social-ecological systems. Marine protected areas (MPAs) are increasingly being promoted as an ocean-based climate solution. However, such claims remain controversial because of the diffuse and poorly synthesized literature on climate benefits of MPAs. To address this knowledge gap, we conducted a systematic literature review of 22,403 publications spanning 241 MPAs and analyzed these across 16 ecological and social pathways through which MPAs could contribute to climate change mitigation and adaptation. Our meta-analysis demonstrates that marine conservation can significantly enhance carbon sequestration, coastal protection, biodiversity, and the reproductive capacity of marine organisms as well as fishers’ catch and income. Most of these benefits are only achieved in fully or highly protected areas and increase with MPA age. Although MPAs alone cannot offset all climate change impacts, they are a useful tool for climate change mitigation and adaptation of social-ecological systems. IntroductionClimate change has started to undermine human well-being and planetary health, generating a sense of urgency to identify effective mitigation and adaptation strategies.1IPCCClimate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.2022https://www.ipcc.ch/report/ar6/wg2/Google Scholar Recent years have seen a growing focus on the ocean’s central role in climate2IPCCIPCC Special Report on the Ocean and Cryosphere in a Changing Climate.2019https://www.ipcc.ch/srocc/Google Scholar as well as an increase in associated advocacy efforts. This is reflected, among other things, in the increasing inclusion of ocean issues in nationally determined contributions for climate mitigation and adaptation.3Gallo N.D. Victor D.G. Levin L.A. Ocean commitments under the Paris agreement.Nat. Clim. 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Horta e Costa B. Pike E.P. Kingston N. Laffoley D. Sala E. Claudet J. et al.The MPA Guide: a framework to achieve global goals for the ocean.Science. 2021; 373: eabf0861https://doi.org/10.1126/science.abf0861Google Scholar their ability to contribute to the resilience of marine social-ecological systems to climate change or to contribute to carbon sequestration remains highly controversial.10Roberts C.M. O’Leary B.C. McCauley D.J. Cury P.M. Duarte C.M. Lubchenco J. Pauly D. Sáenz-Arroyo A. Sumaila U.R. Wilson R.W. et al.Marine reserves can mitigate and promote adaptation to climate change.Proc. Natl. Acad. Sci. USA. 2017; 114: 6167-6175https://doi.org/10.1073/pnas.1701262114Google Scholar,11Hilborn R. Are MPAs effective?.ICES J. Mar. Sci. 2018; 75: 1160-1162https://doi.org/10.1093/icesjms/fsx068Google Scholar,12Bates A.E. Cooke R.S. Duncan M.I. Edgar G.J. Bruno J.F. Benedetti-Cecchi L. Côté I.M. Lefcheck J.S. Costello M.J. 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Some argue that the increases in abundance, biomass, and biodiversity of fished populations occurring in MPAs15Zupan M. Fragkopoulou E. Claudet J. Erzini K. Horta e Costa B. Gonçalves E.J. Marine partially protected areas: drivers of ecological effectiveness.Front. Ecol. Environ. 2018; 16: 381-387https://doi.org/10.1002/fee.1934Google Scholar,16Lester S. Halpern B. Grorud-Colvert K. Lubchenco J. Ruttenberg B. Gaines S. Airamé S. Warner R. Biological effects within no-take marine reserves: a global synthesis.Mar. Ecol. Prog. Ser. 2009; 384: 33-46https://doi.org/10.3354/meps08029Google Scholar,17Giakoumi S. Scianna C. Plass-Johnson J. Micheli F. Grorud-Colvert K. Thiriet P. Claudet J. Di Carlo G. Di Franco A. Gaines S.D. et al.Ecological effects of full and partial protection in the crowded Mediterranean Sea: a regional meta-analysis.Sci. Rep. 2017; 7: 8940https://doi.org/10.1038/s41598-017-08850-wGoogle Scholar promote other ecological outcomes, such as reproductive output, genetic diversity, or ecosystem stability,10Roberts C.M. O’Leary B.C. McCauley D.J. Cury P.M. Duarte C.M. Lubchenco J. Pauly D. Sáenz-Arroyo A. Sumaila U.R. Wilson R.W. et al.Marine reserves can mitigate and promote adaptation to climate change.Proc. Natl. Acad. Sci. USA. 2017; 114: 6167-6175https://doi.org/10.1073/pnas.1701262114Google Scholar ultimately contributing to the adaptive potential of marine ecosystems to climate change.18O’Leary J.K. Micheli F. Airoldi L. Boch C. De Leo G. Elahi R. Ferretti F. Graham N.A.J. Litvin S.Y. Low N.H. et al.The resilience of marine ecosystems to climatic disturbances.BioScience. 2017; 67: 208-220https://doi.org/10.1093/biosci/biw161Google Scholar,19Miller D.D. Ota Y. Sumaila U.R. Cisneros-Montemayor A.M. Cheung W.W.L. Adaptation strategies to climate change in marine systems.Glob. Chang. Biol. 2018; 24: e1-e14https://doi.org/10.1111/gcb.13829Google Scholar,20Bernhardt J.R. Leslie H.M. Resilience to climate change in coastal marine ecosystems.Ann. Rev. Mar. Sci. 2013; 5: 371-392https://doi.org/10.1146/annurev-marine-121211-172411Google ScholarHowever, few studies have directly tested the effects of MPAs on climate change adaptative potential, and the existing literature shows contrasting results.21Freedman R.M. Brown J.A. Caldow C. Caselle J.E. Marine protected areas do not prevent marine heatwave-induced fish community structure changes in a temperate transition zone.Sci. Rep. 2020; 10: 21081https://doi.org/10.1038/s41598-020-77885-3Google Scholar,22Mellin C. Aaron MacNeil M. Cheal A.J. Emslie M.J. Julian Caley M. Marine protected areas increase resilience among coral reef communities.Ecol. Lett. 2016; 19: 629-637https://doi.org/10.1111/ele.12598Google Scholar A great amount of literature has shown that MPAs failed to protect coral reefs from bleaching during heat waves.23Bruno J.F. Côté I.M. Toth L.T. Climate change, coral loss, and the curious case of the parrotfish paradigm: why don’t marine protected areas improve reef resilience?.Ann. Rev. Mar. Sci. 2019; 11: 307-334https://doi.org/10.1146/annurev-marine-010318-095300Google Scholar In some instances, coral loss has even been shown to be greater in MPAs than in unprotected areas. This phenomenon, referred to as the “protection paradox,”12Bates A.E. Cooke R.S. Duncan M.I. Edgar G.J. Bruno J.F. Benedetti-Cecchi L. Côté I.M. Lefcheck J.S. Costello M.J. Barrett N. et al.Climate resilience in marine protected areas and the ‘Protection Paradox.Biol. Conserv. 2019; 236: 305-314https://doi.org/10.1016/j.biocon.2019.05.005Google Scholar has fueled much of the opposition in advocating MPAs as a tool for climate adaptation.The effects of marine conservation on social adaptive potential are another contentious topic because millions of livelihoods directly depend on fisheries for income and food security. Although MPAs have been shown to provide benefits to fisheries because of spillover of fish from protected to fished areas,24Di Lorenzo M. Guidetti P. Di Franco A. Calò A. Claudet J. Assessing spillover from marine protected areas and its drivers: a meta-analytical approach.Fish Fish. 2020; 21: 906-915https://doi.org/10.1111/faf.12469Google Scholar controversy remains regarding the overall costs and benefits to fishing communities.25Ban N.C. Gurney G.G. Marshall N.A. Whitney C.K. Mills M. Gelcich S. Bennett N.J. Meehan M.C. Butler C. Ban S. et al.Well-being outcomes of marine protected areas.Nat. Sustain. 2019; 2: 524-532https://doi.org/10.1038/s41893-019-0306-2Google Scholar,26Hilborn R. Policy: marine biodiversity needs more than protection.Nature. 2016; 535: 224-226https://doi.org/10.1038/535224aGoogle Scholar,27Cinner J. Huchery C. A comparison of social outcomes associated with different fisheries Co-management institutions: fisheries co-management.Conserv. Lett. 2014; 7: 224-232https://doi.org/10.1111/conl.12057Google Scholar Because coastal populations are among the most vulnerable to climate change,1IPCCClimate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.2022https://www.ipcc.ch/report/ar6/wg2/Google Scholar,2IPCCIPCC Special Report on the Ocean and Cryosphere in a Changing Climate.2019https://www.ipcc.ch/srocc/Google Scholar it is paramount to identify solutions that will not further negatively impact their adaptive capacity.28Cinner J.E. Adger W.N. Allison E.H. Barnes M.L. Brown K. Cohen P.J. Gelcich S. Hicks C.C. Hughes T.P. Lau J. et al.Building adaptive capacity to climate change in tropical coastal communities.Nat. Clim. Chang. 2018; 8: 117-123https://doi.org/10.1038/s41558-017-0065-xGoogle Scholar,29Mora C. Wei C.-L. Rollo A. Amaro T. Baco A.R. Billett D. Bopp L. Chen Q. Collier M. Danovaro R. et al.Biotic and human vulnerability to projected changes in ocean biogeochemistry over the 21st century.PLoS Biol. 2013; 11: e1001682https://doi.org/10.1371/journal.pbio.1001682Google Scholar However, no synthesis of the literature examining how MPAs impact social adaptive potential exists, casting doubt on whether marine conservation can be used as a holistic tool that benefits marine ecosystems and coastal communities.30Cinner J.E. Zamborain-Mason J. Gurney G.G. Graham N.A.J. MacNeil M.A. Hoey A.S. Mora C. Villéger S. Maire E. McClanahan T.R. et al.Meeting fisheries, ecosystem function, and biodiversity goals in a human-dominated world.Science. 2020; 368: 307-311https://doi.org/10.1126/science.aax9412Google ScholarThe debate has also centered on the ability of MPAs to provide climate mitigation benefits, notably through increased carbon sequestration from rebuilt fish populations or from undisturbed sediments from trawling bans.13Epstein G. Middelburg J.J. Hawkins J.P. Norris C.R. Roberts C.M. The impact of mobile demersal fishing on carbon storage in seabed sediments.Glob. Chang. Biol. 2022; 28: 2875-2894https://doi.org/10.1111/gcb.16105Google Scholar,31Mariani G. Cheung W.W.L. Lyet A. Sala E. Mayorga J. Velez L. Gaines S.D. Dejean T. Troussellier M. Mouillot D. Let more big fish sink: fisheries prevent blue carbon sequestration—half in unprofitable areas.Sci. Adv. 2020; 6: eabb4848https://doi.org/10.1126/sciadv.abb4848Google Scholar Clarity regarding how ocean conservation contributes to ecological adaptation, social adaptation, and climate change mitigation is urgently needed to ensure that effective ocean-based strategies are adopted in climate change policies.To address these knowledge gaps, we identified the potential pathways through which MPAs could contribute to climate change mitigation and adaptation (hereafter referred to as “climate pathways”). A layered typology was used to classify these climate pathways: first along mitigation and adaptation dimensions and then distinguishing among ecological and social dimensions of adaptation. We then carried out a systematic literature review and summarized the results of all empirical studies documenting MPA outcomes on these climate pathways using vote counting and a meta-analytical approach. Vote counting (i.e., calculating the fraction of studies reporting positive, negative, or neutral outcomes) allows us to synthesize results from both qualitative and quantitative studies and to overcome some publication biases associated with meta-analysis. For these reasons, it is commonly used in social science,25Ban N.C. Gurney G.G. Marshall N.A. Whitney C.K. Mills M. Gelcich S. Bennett N.J. Meehan M.C. Butler C. Ban S. et al.Well-being outcomes of marine protected areas.Nat. Sustain. 2019; 2: 524-532https://doi.org/10.1038/s41893-019-0306-2Google Scholar,32Mascia M.B. Claus C.A. Naidoo R. Impacts of marine protected areas on fishing communities.Conserv. Biol. 2010; 24: 1424-1429https://doi.org/10.1111/j.1523-1739.2010.01523.xGoogle Scholar as well as in ecology.33Wittmann A.C. Pörtner H.O. Sensitivities of extant animal taxa to ocean acidification.Nat. Clim. Chang. 2013; 3: 995-1001https://doi.org/10.1038/nclimate1982Google Scholar,34Leung J.Y.S. Zhang S. Connell S.D. Is ocean acidification really a threat to marine calcifiers? A systematic review and meta-analysis of 980+ studies spanning two decades.Small. 2022; 18: 2107407https://doi.org/10.1002/smll.202107407Google Scholar When sufficient quantitative data were available to perform meta-analysis, we also quantified the direction, magnitude, and uncertainty of MPA outcomes on climate pathways. Because previous analyses have shown that high levels of protection are required to achieve ecological15Zupan M. Fragkopoulou E. Claudet J. Erzini K. Horta e Costa B. Gonçalves E.J. Marine partially protected areas: drivers of ecological effectiveness.Front. Ecol. Environ. 2018; 16: 381-387https://doi.org/10.1002/fee.1934Google Scholar and social35Turnbull J.W. Johnston E.L. Clark G.F. Evaluating the social and ecological effectiveness of partially protected marine areas.Conserv. Biol. 2021; 35: 921-932https://doi.org/10.1111/cobi.13677Google Scholar outcomes, we also investigated whether this was a necessary condition for MPAs to produce climate mitigation and adaptation benefits.Our literature review found that marine conservation enhances most ecological and social climate pathways. Meta-analyses showed that MPAs significantly increase carbon sequestration, coastal protection, biodiversity, and the reproductive capacity of marine organisms as well as fishers’ catch and income. However, these benefits were only achieved under full or high levels of protection. Our study provides evidence that MPAs constitute an effective solution for climate change mitigation and adaptation of the intertwined components of social-ecological systems.MPA mitigation and adaptation pathwaysSixteen pathways through which MPAs could contribute to climate change mitigation and adaptation were identified by drawing on reviews of social and ecological outcomes of MPAs10Roberts C.M. O’Leary B.C. McCauley D.J. Cury P.M. Duarte C.M. Lubchenco J. Pauly D. Sáenz-Arroyo A. Sumaila U.R. Wilson R.W. et al.Marine reserves can mitigate and promote adaptation to climate change.Proc. Natl. Acad. Sci. USA. 2017; 114: 6167-6175https://doi.org/10.1073/pnas.1701262114Google Scholar,12Bates A.E. Cooke R.S. Duncan M.I. Edgar G.J. Bruno J.F. Benedetti-Cecchi L. Côté I.M. Lefcheck J.S. Costello M.J. Barrett N. et al.Climate resilience in marine protected areas and the ‘Protection Paradox.Biol. Conserv. 2019; 236: 305-314https://doi.org/10.1016/j.biocon.2019.05.005Google Scholar,20Bernhardt J.R. Leslie H.M. Resilience to climate change in coastal marine ecosystems.Ann. Rev. Mar. Sci. 2013; 5: 371-392https://doi.org/10.1146/annurev-marine-121211-172411Google Scholar,25Ban N.C. Gurney G.G. Marshall N.A. Whitney C.K. Mills M. Gelcich S. Bennett N.J. Meehan M.C. Butler C. Ban S. et al.Well-being outcomes of marine protected areas.Nat. Sustain. 2019; 2: 524-532https://doi.org/10.1038/s41893-019-0306-2Google Scholar,28Cinner J.E. Adger W.N. Allison E.H. Barnes M.L. Brown K. Cohen P.J. Gelcich S. Hicks C.C. Hughes T.P. Lau J. et al.Building adaptive capacity to climate change in tropical coastal communities.Nat. Clim. Chang. 2018; 8: 117-123https://doi.org/10.1038/s41558-017-0065-xGoogle Scholar (Table S1). Two climate pathways contributed to climate mitigation (carbon sequestration and local acidity buffering) and 14 to climate adaptation (Figure 1). Social adaptation pathways were derived from the five pillars of social adaptive capacity28Cinner J.E. Adger W.N. Allison E.H. Barnes M.L. Brown K. Cohen P.J. Gelcich S. Hicks C.C. Hughes T.P. Lau J. et al.Building adaptive capacity to climate change in tropical coastal communities.Nat. Clim. Chang. 2018; 8: 117-123https://doi.org/10.1038/s41558-017-0065-xGoogle Scholar: assets, flexibility, agency, learning, and social organization, to which was added food security.30Cinner J.E. Zamborain-Mason J. Gurney G.G. Graham N.A.J. MacNeil M.A. Hoey A.S. Mora C. Villéger S. Maire E. McClanahan T.R. et al.Meeting fisheries, ecosystem function, and biodiversity goals in a human-dominated world.Science. 2020; 368: 307-311https://doi.org/10.1126/science.aax9412Google Scholar Ecological pathways were derived from climate adaptation pathways described previously:10Roberts C.M. O’Leary B.C. McCauley D.J. Cury P.M. Duarte C.M. Lubchenco J. Pauly D. Sáenz-Arroyo A. Sumaila U.R. Wilson R.W. et al.Marine reserves can mitigate and promote adaptation to climate change.Proc. Natl. Acad. Sci. USA. 2017; 114: 6167-6175https://doi.org/10.1073/pnas.1701262114Google Scholar,12Bates A.E. Cooke R.S. Duncan M.I. Edgar G.J. Bruno J.F. Benedetti-Cecchi L. Côté I.M. Lefcheck J.S. Costello M.J. Barrett N. et al.Climate resilience in marine protected areas and the ‘Protection Paradox.Biol. Conserv. 2019; 236: 305-314https://doi.org/10.1016/j.biocon.2019.05.005Google Scholar,20Bernhardt J.R. Leslie H.M. Resilience to climate change in coastal marine ecosystems.Ann. Rev. Mar. Sci. 2013; 5: 371-392https://doi.org/10.1146/annurev-marine-121211-172411Google Scholar connectivity, phenotypic plasticity, genetic diversity, biodiversity, stability, reproductive output, body condition, and coastal protection. Up to two indicators were selected to measure each pathway based on the most common indicators used in the reviewed studies. Additional indicators were also investigated when they allowed us to quantify aspects of the studied pathways not yet captured by the first two indicators (Table S2; Figure S4). The definition of each pathway and the units used to measure each indicator are detailed in Table S2. For two pathways (carbon sequestration and coastal protection), we also included all studies comparing exploited and preserved marine areas even when not officially labeled MPAs. This was done because the literature documenting the effect of preservation initiatives, comparable with MPAs, is abundant, whereas almost no study directly documenting MPAs is available.The systematic literature review on MPA effects on climate pathways generated a total of 22,403 publications, of which 378 were included in vote counting, providing insights from 241 different MPAs. Publications were unevenly distributed among continents (Figures 1B–1D), with most ecological adaptation pathways studied in Europe and most mitigation and social adaptation pathways studied in Asia (Figure S2). We found empirical evidence documenting the effects of MPAs on all climate pathways except acidity buffering, connectivity, and phenotypic plasticity (Figure 1). Eight climate pathways had sufficient quantitative data (n > 3) to perform a meta-analysis.Marine conservation contributes to carbon sequestrationWe investigated the effects of marine conservation on the carbon (C) sequestration capacity of six marine C sinks: three blue C ecosystems (mangrove, tidal marshes, and seagrass), which have already been recognized by the Intergovernmental Panel on Climate Change (IPCC) for C accounting schemes,36Groupe d’experts intergouvernemental sur l’évolution du climat2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands: Methodological Guidance on Lands with Wet and Drained Soils, and Constructed Wetlands for Wastewater Treatment. Intergovernmental Panel on Climate Change, 2014Google Scholar as well as sediments, macroalgae, and fish.31Mariani G. Cheung W.W.L. Lyet A. Sala E. Mayorga J. Velez L. Gaines S.D. Dejean T. Troussellier M. Mouillot D. Let more big fish sink: fisheries prevent blue carbon sequestration—half in unprofitable areas.Sci. Adv. 2020; 6: eabb4848https://doi.org/10.1126/sciadv.abb4848Google Scholar,37Krause-Jensen D. Lavery P. Serrano O. Marbà N. Masque P. Duarte C.M. Sequestration of macroalgal carbon: the elephant in the Blue Carbon room.Biol. Lett. 2018; 14: 20180236https://doi.org/10.1098/rsbl.2018.0236Google Scholar C sequestration was defined as organic C stored for over 100 years.38Griscom B.W. Adams J. Ellis P.W. Houghton R.A. Lomax G. Miteva D.A. Schlesinger W.H. Shoch D. Siikamäki J.V. Smith P. et al.Natural climate solutions.Proc. Natl. Acad. Sci. USA. 2017; 114: 11645-11650https://doi.org/10.1073/pnas.1710465114Google Scholar Mean effect sizes (log response ratios [lnRR], 95% confidence interval) indicated significant increases in C sequestration in preserved or restored seagrass (lnRR = 0.76 ± 0.34) and mangrove (lnRR = 0.75 ± 0.14) ecosystems in comparison with similar areas undergoing human pressure (e.g., thinning, anchoring, conversion to plantations). Similarly, sediments in untrawled seabed sequestered significantly more C than areas exposed to trawling (lnRR = 0.13 ± 0.10). Conservation had no effect on C sequestered by tidal marshes (Figure 2D ), mostly because conversion of unprotected marsh into agricultural land increased C sequestered in plant biomass and in the soil.39Yang W. Xia L. Zhu Z. Jiang L. Cheng X. An S. Shift in soil organic carbon and nitrogen pools in different reclaimed lands following intensive coastal reclamation on the coasts of eastern China.Sci. Rep. 2019; 9: 5921https://doi.org/10.1038/s41598-019-42048-6Google Scholar Partial (e.g., thinning, anchoring) or full (e.g., clear cutting, excavating) degradation of mangroves and seagrass resulted in similar decreases of sequestered C, indicating that even low levels of human impact result in important C emissions (Figure S6). No studies documented the effect of protection on the quantity of sequestered C originating from fish or macroalgae biomass. However, many studies have shown that MPAs significantly increase fish biomass (lnRR = 1.10 ± 0.58),16Lester S. Halpern B. Grorud-Colvert K. Lubchenco J. Ruttenberg B. Gaines S. Airamé S. Warner R. Biological effects within no-take marine reserves: a global synthesis.Mar. Ecol. Prog. Ser. 2009; 384: 33-46https://doi.org/10.3354/meps08029Google Scholar which can serve as a proxy for C sequestration because a portion of that biomass undergoes exportation and is subsequently sequestered in the deep sea.40Saba G.K. Burd A.B. Dunne J.P. Hernández-León S. Martin A.H. Rose K.A. Salisbury J. Steinberg D.K. Trueman C.N. Wilson R.W. et al.Toward a better understanding of fish-based contribution to ocean carbon flux.Limnol. Oceanogr. 2021; 66: 1639-1664https://doi.org/10.1002/lno.11709Google Scholar This is supported by several studies that calculated large impacts of fisheries on C sequestration from fish biomass removal.31Mariani G. Cheung W.W.L. Lyet A. Sala E. Mayorga J. Velez L. Gaines S.D. Dejean T. Troussellier M. Mouillot D. Let more big fish sink: fisheries prevent blue carbon sequestration—half in unprofitable areas.Sci. Adv. 2020; 6: eabb4848https://doi.org/10.1126/sciadv.abb4848Google Scholar,41Martin S.L. Ballance L.T. Groves T. An ecosystem services perspective for the oceanic eastern tropical pacific: commercial fisheries, carbon storage, recreational fishing, and biodiversity.Front. Mar. Sci. 2016; 3https://doi.org/10.3389/fmars.2016.00050Google Scholar However, this remains an indirect measurement of C sequestration, and more research is needed to quantify the exportation rates of organic C from fish biomass toward sediments.42Stafford R. Boakes Z. Hall A.E. Jones G.C.A. The role of predator removal by fishing on ocean carbon dynamics.Anthr. Sci. 2022; 1: 204-210https://doi.org/10.1007/s44177-021-00005-xGoogle Scholar Although macroalgae are increasingly being advocated as significant actors in marine C sequestration,37Krause-Jensen D. Lavery P. Serrano O. Marbà N. Masque P. Duarte C.M. Sequestration of macroalgal carbon: the elephant in the Blue Carbon room.Biol. Lett. 2018; 14: 20180236https://doi.org/10.1098/rsbl.2018.0236Google Scholar,43Ortega A. Geraldi N.R. Alam I. Kamau A.A. Acinas S.G. Logares R. Gasol J.M. Massana R. Krause-Jensen D. Duarte C.M. Important contribution of macroalgae to oceanic carbon sequestration.Nat. Geosci. 2019; 12: 748-754https://doi.org/10.1038/s41561-019-0421-8Google Scholar major knowledge gaps remain regarding how marine conservation affects their living biomass and, thus, their contribution to C sequestration.Figure 2Effects of marine protected areas (MPAs) on climate change mitigation and adaptation pathwaysShow full caption(A–C) Climate pathways (A) and direction of reported MPA effects from studies included in the vote-counting analysis (B) and magnitude of outcomes from studies included in the meta-analysis (C). In (B), the x axis indicates the cumulative number of studies reporting positive outcomes (right side of the bar plot, green) and ambiguous, negative, or neutral outcomes (left side of the bar plot). In (C), the x axis indicates the log-transformed ratio of indicators between MPAs and controls. In the case of coastal protection, the effect size was calculated as the Euclidian difference between MPAs and controls, hence the separate scale provided. Values are presented as mean values ± 95% confidence interval. Black dots indicate effect sizes that do not overlap zero and white dots those that overlap zero. Sample sizes (i.e., number of studies) of vote counting and meta-analysis results are indicated by n values. ∗In the case of C sequestration from fish biomass, the effect size was calculated from three previous meta-analyses, representing data from many more individual studies.(D–F) Effect of habitat type (D), protection level (E), and presence of a fully protected area (F) on the capacity of MPAs to provide climate benefits. Colors, sample size, and x axis have the same meaning as in (C). †Effects of full protection on C sequestration (fish biomass only) are reported from Lester et al.16Lester S. Halpern B. Grorud-Colvert K. Lubchenco J. Ruttenberg B. Gaines S. Airamé S. Warner R. Biological effects within no-take marine reserves: a global synthesis.Mar. Ecol. Prog. Ser. 2009; 384: 33-46https://doi.org/10.3354/meps08029Google Scholar ‡Effects of high and low protection on C sequestration (fish biomass only) are reported from Zupan et al.15Zupan M. Fragkopoulou E. Claudet J. Erzini K. Horta e Costa B. Gonçalves E.J. Marine partially protected areas: drivers of ecological effectiveness.Front. Ecol. Environ. 2018; 16: 381-387https://doi.org/10.1002/fee.1934Google ScholarView Large Image Figure ViewerDownload Hi-res image