How do ocean acidification and warming affect global fisheries?

Ocean acidification and ocean warming—direct results of increased atmospheric CO₂—are profoundly altering marine ecosystems, with deeply consequential impacts on global fisheries. These stressors act independently and synergistically, affecting fish physiology, species distributions, food webs, and the socioeconomic foundation of fisheries-dependent communities.

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Ocean Acidification: Mechanisms and Biological ImpactsOcean acidification refers to the ongoing decrease in oceanic pH and carbonate ion concentrations due to absorption of atmospheric CO₂, which has already lowered global surface pH by more than 0.1 units since preindustrial times, and is projected to decrease by an additional 0.10–0.35 units by 2100 if emissions continue unabated [1][2]. This shift in ocean chemistry has cascading biological effects:

• Calcifying organisms—including mollusks, crustaceans, sea urchins, and corals—are directly threatened. Reduced carbonate saturation impedes shell and skeleton formation, weakening organisms that underpin both ecosystems and fisheries. Mollusks, which make up much of global aquaculture and are vital to benthic food webs, are notably vulnerable throughout their life cycles, with observed reductions in survival, growth, and calcification under acidified conditions [3][4][5][6]. For shellfish aquaculture (e.g., abalone, oysters), population-specific physiological traits can confer resilience, but overall industry viability is at risk without selection for tolerant strains [6].

• Early life stages of calcifiers and some non-calcifying fish species experience elevated developmental abnormalities, increased larval mortality, and reduced fertilization rates when exposed to acidified conditions, particularly in multi-stressor scenarios or with low genetic diversity [3][5][6][7]. The magnitude of sensitivity can vary across taxa and populations, but lower rates of successful recruitment in affected species may reduce stock sizes and ecosystem productivity [3][4][5].

• Indirect ecosystem effects occur as declines in primary producers (certain plankton) and changes in competitive dynamics propagate through food webs, potentially reducing the availability of prey for commercially important fish [2][3][7][8].

• Sensory and behavioral effects have also been documented in finfish, including impaired predator detection and altered navigation, which may increase mortality rates in both juvenile and adult stages [3].

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Ocean Warming: Drivers of Change in FisheriesWarming oceans, another major outcome of accumulated greenhouse gases, directly affect fish and marine ecosystems through physiological and ecological pathways:

• Poleward and depth-related shifts in species distributions are now well-established. As water temperatures rise, many fish species shift toward cooler, higher-latitude waters or to deeper habitats, disrupting traditional fishing grounds and challenging existing management frameworks [8][9].

• Changing productivity and food web structure results as ocean warming enhances stratification, reducing nutrient upwelling and thus limiting new primary production in many regions. Reduced primary productivity decreases energy availability for higher trophic levels, leading to declines in aggregate fish community biomass—projected at up to 30% by 2100 in some models [8]. These impacts are especially pronounced in lower-latitude and upwelling-dependent systems.

• Phenological shifts and biological mismatches may arise as the timing of migration, reproduction, and larval development alter, leading to mismatches between spawning and optimal food availability or habitat conditions, impacting recruitment success [9][10][11].

• Disease and metabolic stress are exacerbated by rising temperatures, increasing susceptibility to pathogens and harmful algal blooms, while also elevating metabolic demands, which may not be met under reduced food supply or in hypoxic conditions [8][9][12].

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Synergistic and Cumulative Effects: Multiple StressorsCrucially, ocean acidification and warming interact in complex, often non-additive ways. Experimental and meta-analytical studies show that the negative effects of acidification can be amplified when organisms are concurrently exposed to elevated temperatures [3][13]. For instance:

• Coral reefs, critical for fisheries, suffer major declines in carbonate accretion under both acidification and warming, with projections indicating that, by 2100 under high-emission scenarios, most reefs will be unable to maintain positive growth or provide their ecological functions, including critical habitat and nursery areas for fish [14][15][16].

• Juvenile stages of some benthic invertebrates and sea urchins show resilience to current conditions but significant impairment in growth, development, or survival under co-occurring higher pCO₂ and warming scenarios, especially at projected end-of-century levels [3][13]. Such compounded stresses threaten the persistence of keystone species and alter competitive balances within communities [3][13][17].

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Socioeconomic and Management ImplicationsFisheries not only support food security and livelihoods but also anchor the economies and cultural identities of many coastal communities. The combined impacts of acidification and warming have profound societal consequences:

• Food security and employment may be jeopardized by shifts in species distributions, decreased productivity, and the collapse of shellfish and reef-associated fisheries [18][19]. Vulnerable communities—often in developing countries with limited adaptive capacity—are likely to be most affected, due to their dependence on local fisheries and lack of economic alternatives [18][19].

• Management challenges include reconciling shifting stock ranges with static political boundaries, implementing adaptive, ecosystem-based management, and integrating climate projections into stock assessments and international agreements [2][9][18].

• Potential for adaptation exists, particularly through selective breeding of resilient aquaculture species, improved management practices, and socioeconomic diversification [6]. However, the pace and scope of environmental change may outstrip the ability of many species and societies to adapt, especially under high-emission scenarios [2][14][15].

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Concluding SynthesisOcean acidification and warming represent intersecting, intensifying threats to global fisheries. Acidification impairs the biology of calcifying shellfish and reef builders, undermining the base of many marine food webs and directly jeopardizing shellfish aquaculture and reef-based fishery resources [3][4][6][14][16]. Warming precipitates shifts in species distributions, decreases aggregate fish biomass through altered productivity and increased mortality, and magnifies disease risks [8][9]. When combined, these stressors erode the resilience of marine ecosystems—disrupting food webs, diminishing the capacity of fisheries to support human communities, and challenging the sustainability of resource management [2][3][8][9][14][15][18].

Future resilience of global fisheries will depend both on decisive mitigation efforts to curb greenhouse gas emissions and on proactive adaptation to an ocean that is simultaneously warmer and more acidic than at any point in modern human history [8][14][15][18].