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1. Ocean acidification alters morphology of all otolith types in Clark’s anemonefish ( Amphiprion clarkii )

   https://doi.org/10.7717/peerj.6152  

   Holmberg, Robert J. ; Wilcox-Freeburg, Eric ; Rhyne, Andrew L. ; Tlusty, Michael F. ; Stebbins, Alan ; Nye Jr., Steven W. ; Honig, Aaron ; Johnston, Amy E. ; San Antonio, Christine M. ; Bourque, Bradford ; et al ( January 2019 , PeerJ)

   Ocean acidification, the ongoing decline of surface ocean pH and [CO${}_{3}^{2-}$] due to absorption of surplus atmospheric CO 2 , has far-reaching consequences for marine biota, especially calcifiers. Among these are teleost fishes, which internally calcify otoliths, critical elements of the inner ear and vestibular system. There is evidence in the literature that ocean acidification increases otolith size and alters shape, perhaps impacting otic mechanics and thus sensory perception. Here, larval Clark’s anemonefish, Amphiprion clarkii (Bennett, 1830), were reared in various seawater pCO 2 /pH treatments analogous to future ocean scenarios. At the onset of metamorphosis, all otoliths were removed from each individual fish and analyzed for treatment effects on morphometrics including area, perimeter, and circularity; scanning electron microscopy was used to screen for evidence of treatment effects on lateral development, surface roughness, and vaterite replacement. The results corroborate those of other experiments with other taxa that observed otolith growth with elevated pCO 2 , and provide evidence that lateral development and surface roughness increased as well. Both sagittae exhibited increasing area, perimeter, lateral development, and roughness; left lapilli exhibited increasing area and perimeter while right lapilli exhibited increasing lateral development and roughness; and left asterisci exhibited increasing perimeter, roughness, and ellipticity with increasing pCO 2 . Right lapilli and left asterisci were only impacted by the most extreme pCO 2 treatment, suggesting they are resilient to any conditions short of aragonite undersaturation, while all other impacted otoliths responded to lower concentrations. Finally, fish settlement competency at 10 dph was dramatically reduced, and fish standard length marginally reduced with increasing pCO 2 . Increasing abnormality and asymmetry of otoliths may impact inner ear function by altering otolith-maculae interactions. 

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2. Ocean acidification alters morphology of all otolith types in Clark’s anemonefish (Amphiprion clarkii)

   Robert Holmberg, Eric Wilcox-Freeburg ( July 2018 , PeerJ preprints)

   Ocean acidification, the ongoing decline of surface ocean pH and [CO32-] due to absorption of surplus atmospheric CO2, has far-reaching consequences for marine biota, especially calcifiers. Among these are teleost fishes, which internally calcify otoliths, critical elements of the inner ear and vestibular system. There is evidence in the literature that ocean acidification increases otolith size and alters shape, perhaps impacting otic mechanics and thus sensory perception. However, existing analyses of otolith morphological responses to ocean acidification are limited to 2-dimensional morphometrics and shape analysis. Here, we reared larval Clark’s anemonefish, Amphiprion clarkii (Bennett, 1830), in various seawater pH treatments analogous to future ocean scenarios in a 3x-replicated experimental design. Upon settlement, we removed all otoliths from each individual fish and analyzed them for treatment effects on morphometrics including area, perimeter, and circularity; further, we used scanning electron microscopy to screen otoliths visually for evidence of treatment effects on lateral development, surface roughness, and vaterite replacement. Our results corroborate those of other experiments with other taxa that observed otolith growth with elevated pCO2, and provide evidence that lateral development and surface roughness increased as well; we observed at least one of these effects in all otolith types. Finally, we review previous work investigating ocean acidification impacts on otolith morphology and hypotheses concerning function, placing our observations in context. These impacts may have consequences teleost fitness in the near-future ocean 

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3. Understanding the Metabolic Capacity of Antarctic Fishes to Acclimate to Future Ocean Conditions

   https://doi.org/10.1093/icb/icaa121  

   Todgham, Anne E ; Mandic, Milica ( August 2020 , Integrative and Comparative Biology)

   null (Ed.)

   Synopsis Antarctic fishes have evolved under stable, extreme cold temperatures for millions of years. Adapted to thrive in the cold environment, their specialized phenotypes will likely render them particularly susceptible to future ocean warming and acidification as a result of climate change. Moving from a period of stability to one of environmental change, species persistence will depend on maintaining energetic equilibrium, or sustaining the increased energy demand without compromising important biological functions such as growth and reproduction. Metabolic capacity to acclimate, marked by a return to metabolic equilibrium through physiological compensation of routine metabolic rate (RMR), will likely determine which species will be better poised to cope with shifts in environmental conditions. Focusing on the suborder Notothenioidei, a dominant group of Antarctic fishes, and in particular four well-studied species, Trematomus bernacchii, Pagothenia borchgrevinki, Notothenia rossii, and N. coriiceps, we discuss metabolic acclimation potential to warming and CO2-acidification using an integrative and comparative framework. There are species-specific differences in the physiological compensation of RMR during warming and the duration of acclimation time required to achieve compensation; for some species, RMR fully recovered within 3.5 weeks of exposure, such as P. borchgrevinki, while for other species, such as N. coriiceps, RMR remained significantly elevated past 9 weeks of exposure. In all instances, added exposure to increased PCO2, further compromised the ability of species to return RMR to pre-exposure levels. The period of metabolic imbalance, marked by elevated RMR, was underlined by energetic disturbance and elevated energetic costs, which shifted energy away from fitness-related functions, such as growth. In T. bernacchii and N. coriiceps, long duration of elevated RMR impacted condition factor and/or growth rate. Low growth rate can affect development and ultimately the timing of reproduction, severely compromising the species’ survival potential and the biodiversity of the notothenioid lineage. Therefore, the ability to achieve full compensation of RMR, and in a short-time frame, in order to avoid long term consequences of metabolic imbalance, will likely be an important determinant in a species’ capacity to persist in a changing environment. Much work is still required to develop our understanding of the bioenergetics of Antarctic fishes in the face of environmental change, and a targeted approach of nesting a mechanistic focus in an ecological and comparative framework will better aid our predictions on the effect of global climate change on species persistence in the polar regions. 

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4. Multi‐Decadal Coastal Acidification in the Northern Gulf of Mexico Driven by Climate Change and Eutrophication

   https://doi.org/10.1029/2023GL106300  

   Jiang, Zong‐Pei ; Qin, Cao ; Pan, Yiwen ; Le, Chengfeng ; Rabalais, Nancy ; Turner, Robert Eugene ; Fennel, Katja ; Wang, Kui ; Cai, Wei‐Jun ( March 2024 , Geophysical Research Letters)

   Coastal waters often experience enhanced ocean acidification due to the combined effects of climate change and regional biological and anthropogenic activities. Through reconstructing summertime bottom pH in the northern Gulf of Mexico from 1986 to 2019, we demonstrated that eutrophication‐fueled respiration dominated bottom pH changes on intra‐seasonal and interannual timescales, resulting in recurring acidification coinciding with hypoxia. However, the multi‐decadal acidification trend was principally driven by rising atmospheric CO₂and ocean warming, with more acidified and less buffered hypoxic waters exhibiting a higher rate of pH decline (−0.0023 yr⁻¹) compared to non‐hypoxic waters (−0.0014 yr⁻¹). The cumulative effect of climate‐driven decrease in pH baseline is projected to become more significant over time, while the potential eutrophication‐induced seasonal exacerbation of acidification may lessen with decreasing oxygen availability resulting from ocean warming. Mitigating coastal acidification requires both global reduction in CO₂emissions and regional management of riverine nutrient loads.

    

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5. Going with the flow: the role of ocean circulation in global marine ecosystems under a changing climate

   https://doi.org/10.1111/gcb.13586  

   van Gennip, Simon J. ; Popova, Ekaterina E. ; Yool, Andrew ; Pecl, Gretta T. ; Hobday, Alistair J. ; Sorte, Cascade J. B. ( January 2017 , Global Change Biology)

   Ocean warming, acidification, deoxygenation and reduced productivity are widely considered to be the major stressors to ocean ecosystems induced by emissions ofCO₂. However, an overlooked stressor is the change in ocean circulation in response to climate change. Strong changes in the intensity and position of the western boundary currents have already been observed, and the consequences of such changes for ecosystems are beginning to emerge. In this study, we address climatically induced changes in ocean circulation on a global scale but relevant to propagule dispersal for species inhabiting global shelf ecosystems, using a high‐resolution global ocean model run under theIPCC RCP8.5 scenario. The ¼ degree model resolution allows improved regional realism of the ocean circulation beyond that of availableCMIP5‐class models. We use a Lagrangian approach forced by modelled ocean circulation to simulate the circulation pathways that disperse planktonic life stages. Based on trajectory backtracking, we identify present‐day coastal retention, dominant flow and dispersal range for coastal regions at the global scale. Projecting into the future, we identify areas of the strongest projected circulation change and present regional examples with the most significant modifications in their dominant pathways. Climatically induced changes in ocean circulation should be considered as an additional stressor of marine ecosystems in a similar way to ocean warming or acidification.

    

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