Tagged tuna graphic by Nancy Hulbirt, SOEST Illustration.

PFRP Oceanography Projects

Ocean Acidification Impacts on Tropical Tuna Populations

Progress Reports: FY 2012, FY 2011

Project Summary

The unaccounted impacts of ocean acidification (and warming) upon tuna stocks in the Pacific (and globally) represent a serious risk to the achievement of sustainability based management objectives for both Regional Fisheries Management Organisations (RFMOS) and for the policies of sovereign states responsible for tuna fisheries management in the Pacific region. Research has demonstrated that the early life history stages of some fish species (and numerous other marine organisms) are sensitive to ocean acidification levels that are projected to occur by the end of this century. Those findings have significant implications for future recruitment success and population levels for those species. Utilising the long established expertise and unique facilities at the IATTC’s Achotines Laboratory in Panama, the first year of this project aims to elucidate the impacts of projected ocean acidification levels upon processes and life history stages of yellowfin tuna (Thunnus albacores) that are considered critical to recruitment success: sperm motility, fertilisation rates, embryonic development, hatching rates, condition, development, growth and survival in pre- and post-feeding larvae. Empirical results from the laboratory trials will then be used, in conjunction with physical oceanographic data from ocean acidification projection models, to parameterise the SEAPODYM model and evaluate the impact of ocean acidification upon the distribution and abundance of yellowfin tuna in the Pacific Ocean. The outputs from this project will reduce uncertainty regarding future stock trends as provided to tuna RFMOs in the Pacific, increasing the likelihood that these organisations can make decisions that ultimately achieve sustainability based management objectives.

Potential Impacts of Ocean Acidification upon Tuna Populations

Changes in water chemistry associated with increased CO2 are expected to impact upon tuna populations, and this sensitivity is expected to vary depending on the specific developmental stage. For productive species like tuna, the rate of survival typically increases as fish develop and mature, and the environmental processes that significantly affect recruitment numbers act primarily upon the early life history stages (Pepin, 1991; Ferron and Leggett, 1994). Only a small proportion of larvae survive through to adulthood, with the consequence that even a tiny change in the mortality rate during these stages can have orders of magnitude greater effect on the number of recruits added to the adult population (Pepin, 1991; Buckley et al., 1999). Small changes have large implications for fisheries and their ability to gain maximum yields from stock while not compromising the reproductive capacity of the populations.

In the only known relevant experiment involving tuna, Kikkawa and colleagues (2003) found that 100% mortality of eggs of Eastern little tuna (Euthynnus affinis) occurred within 24 hours of exposure to elevated pCO2 levels. However, the levels tested far exceeded those predicted using IPCC scenarios and these results cannot be used to confidently imply responses under projected ocean acidification levels.

However, concern over the potential impacts of ocean acidification on tuna populations arises from the rapidly growing body of evidence indicating significant negative effects on the physiology, growth and survival of a diverse range of other fish and marine organisms, in response to elevated CO2 levels (Fabry et al. 2008; Guinotte and Fabry, 2008; Raven et al., 2005). There are two main mechanisms by which elevated pCO2 and associated changes in ocean chemistry (including decreased pH) adversely impact marine organisms, these being via decreased carbonate saturation state, which directly affects calcification rates, and via disturbance to acid–base physiology (Fabry et al. 2008; Guinotte and Fabry, 2008). Indirect impacts upon a given organism or population are also expected to occur due to direct impacts upon other species within the ecosystems they are part of.

The reduction in the availability of carbonate ions (reduced carbonate saturation) due to increased CO2 and lowered pH (Feeley et al. 2004) makes calcification processes much more difficult for organisms which build skeletons, shells or other structures out of CaCO3, and in undersaturated waters, dissolution of CaCO3 is favoured (Guinotte and Fabry, 2008). Decreased calcification in response to the reduced carbonate saturation state has been demonstrated in numerous species of coral, coccolithophores, molluscs, echinoderms and other calcifying organisms (e.g. Raven et al., 2005).

However, little attention has been given to the potential impacts on the development/growth of fish otoliths, which play a critical role in fish balance and hearing, and which are in large part comprised of aragonite, a form of calcium carbonate. The only known study, that of Checkley et al (2009), surprisingly found that larval white sea bass, grown under elevated CO2 conditions, produced significantly larger otoliths compared to fish of the same size/age grown under control conditions. However, the impact of abnormally large otoliths (for size) upon fish condition and survival is still unknown (Checkley et al., 2009) and the impact of ocean acidification on otolith formation may depend on species specific capacity for acid-base regulation in the tissues surrounding the otoliths (Fabry et al 2008). Given the importance of otoliths to fish movement and behaviour determining potential impacts on tuna is a priority.

Acid base metabolism is another key area of potential impact in tuna. Increased partial pressure of CO2 in the blood (hypercapnia) due to increased environmental pCO2, can induce acidosis in body tissues and fluids of larger marine organisms including fish (Portner et al., 2004), with evidence that this can impact on numerous processes including the oxygen carrying capacity of blood (Portner and Reipschlager, 1996), protein synthesis and growth (Langerbuch and Portner, 2003) and reproduction (Portner et al, 2004). Such impacts are also likely to vary between developmental stages.

Unfortunately, studies on fish species which attempt to examine the likely impacts of ocean acidification on fish metabolism are relatively few. Many studies have tested for the potential effects of CO2 levels which are much higher than projected under IPCC scenarios (Fabry et al 2008). Those studies have typically found very high mortality levels (Kikkawa et al., 2006; Hayashi et al. 2004), including in early developmental stages (eggs, larva) (Kikkawa et al. 2003, Ishimatsu et al. 2005) and other effects including reduced cardiac output (Ishimatsu et al. 2004) and metabolic capacity (Michaelidis et al. 2007). However, for such information to be relevant to the management of fisheries, they clearly need to be conducted through simulating the ocean chemistry conditions (CO2 and pH levels) that are reflective of those predicted using the IPCC scenarios. Only very recently has research been presented (to the International Symposium on “Climate Change Effects on Fish and Fisheries: Forecasting Impacts, Assessing Ecosystem Responses, and Evaluating Management Strategies”, 25-29 April 2010) on ocean acidification impacts on larval fish using IPCC projections and these results are as yet unpublished in scientific journals, but suggest that susceptibility to ocean acidification will be species specific (Hollowed et al, 2010 and symposium abstracts therein).

Evidence has also been found for impacts of ocean acidification upon processes critical to reproductive success in marine organisms, namely gamete viability, fertilisation rates and embryonic development. Havenhand and colleagues (2008) tested the response of sea urchin gametes and larvae to seawater with CO2 reduced pH by -0.4, (the upper limit of projected change by 2100) and found statistically significant reductions in sperm swimming speed and percent sperm motility and fertilisation rates (down 24%) and subsequent embryonic development. This study emphasises the importance of using CO2 and pH levels predicted using IPCC scenarios and its findings suggest that it will be critically important to examine gamete and fertilisation sensitivities in other broadcast spawning marine species (including tuna) for which sperm are exposed to environmental pH prior to egg fertilisation. Similar effects on sperm activation and motility were found for white sturgeon (Ingerman et al. 2002), further emphasising the potential effects in fish. Similar effects on fertilisation and sperm motility have been found in other studies of sea urchin (Kurihara et al 2004).

Many environmental factors are thought to contribute to recruitment variation including water temperature (e.g. Buckley et al 1990), food availability/starvation (e.g. Lett and Kohler, 1976) and predation (e.g. Leggett and Deblois, 1994). The synergistic impacts of pH in combination with other environmental stressors likely to be encountered in the future (increased temperature) and encountered normally (starvation) may better define the likely direct impacts of ocean acidification upon tuna recruitment.


The unaccounted impacts of ocean acidification (and warming) upon tuna stocks in the Pacific (and globally) represent a serious risk to the achievement of sustainability based management objectives for both Regional Fisheries Management Organisations and for the policies of sovereign states responsible for fisheries management in the Pacific region. The higher risk expected for early life history stages and the observations from other marine species suggest that initial efforts to elucidate the impacts of projected ocean acidification upon tuna populations should focus on processes and stages that are critical to recruitment success: gamete impacts, fertilisation rates, embryonic development, hatching rates, condition, development, growth and survival in pre and post feeding larvae. To understand the implications for tuna population dynamics and for tuna fisheries, these potential effects need to be tested and taken into account in the population models currently used to evaluate stock dynamics in the Pacific Ocean. Yellowfin tuna has been chosen as the initial subject of these investigations, given that the required facilities and expertise to conduct these experiments for yellowfin tuna already exist and it is a key target species in both the WCPO and EPO.


The objectives of this project are three-fold:

  1. Firstly, to collect and collate the experimental data necessary to evaluate the potential impacts of altered gamete, fertilisation, embryonic development, hatching and larvae ecology from projected increases in ocean acidity in the Pacific Ocean for yellowfin tuna.
  2. Secondly, to utilize the experimental data to parameterise the SEAPODYM model to evaluate the impact of projected ocean acidification (and warming) upon the distribution and abundance of yellowfin tuna.
  3. Thirdly, provide information on the potential impacts of ocean acidification upon tuna stocks, in particular yellowfin tuna, to RFMOs for consideration in management decision making processes.

Expected Outcomes

The research plan is based around a two-year time line. The expected outcome at the end of two years is a model (SEAPODYM) based evaluation of the expected impact of ocean acidification upon the distribution and abundance of yellowfin tuna in the Pacific Ocean. The results from this modeling will be written up and reported to the Scientific Committees (or equivalent) of the WCPFC, IATTC and WPFMC. This information will enhance the capacity of these RFMOs to make more informed decisions regarding the management of the tuna resources, particularly with regard to attaining key sustainability related objectives.

Funding for this project to be available late 2010.

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Buckley, L.J., Smigelski, A.S., Halavik, T.A. and Laurence, G.C. 1990. Effects of water temperature on size and biochemical composition of winter flounder Pseudopleuronectes americanus at hatching and feeding initiation. Fish. Bull. 88: 419-428.

Buckley, L., Caldarone, E. and Ong, T.L. 1999. RNA-DNA ratio and other nucleic acid-based indicators for growth and condition of marine fishes. Hydrobiologia 401: 265-277.

Checkley, D.M., Dickson, A.G., Takahashi, M., Radich, J.A., Eisenkolf, N., and Asch, R. 2009. Elevated CO2 enhances otolith growth in young fish. Science 324: 1683.

Fabry, V. J., Seibel, B. A., Feely, R. A., and Orr, J. C. 2008. Impacts of ocean acidification on marine fauna and ecosystem processes. – ICES J. Mar.Sci., 65: 414–432.

Feely, R. A., Sabine, C. L., Lee, K., Berelson,W., Kleypas, J., Fabry, V. J., and Millero, F. J. 2004. Impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science, 305: 362–366.

Ferron, A. and Leggett, W.C. 1994. An appraisal of condition measures for marine fish larvae. Adv. Mar. Biol. 30: 217-303.

Guinotte, J.M., and Fabry, V. 2008. Ocean Acidification and Its Potential Effects on Marine Ecosystems. Ann. N.Y. Acad. Sci. 1134: 320–342.

Havenhand, J.N., Buttler, F.R., Thorndyke, M.T. & Williamson, J.E. 2008. Near-future levels of ocean acidification reduce fertilization success in a sea urchin. Cur. Biol. 18; 15.

Hayashi, M., Kita, J., and Ishimatsu, A. 2004. Acid-base responses to lethal aquatic hypercapnia in three marine fishes. Mar Biol., 144: 153–160.

Hollowed, A., Barange, M., Ito,S., Kim, S., and Loeng, H. 2010. International Symposium on “Climate Change Effects on Fish and Fisheries: Forecasting Impacts, Assessing Ecosystem Responses, and Evaluating Management Strategies”, 26-30 April 2010, Sendai, Japan.

Ingermann, R. L., Holcomb, M. , Robinson, M. L. and Cloud, J. G. 2002. Carbon dioxide and pH affect sperm motility of white sturgeon (Acipenser transmontanus) J. Exp. Biol. 205, 2885–2890.

Ishimatsu, A., Hayashi, M., and Lee, S. 2005. Physiological effects on fishes in a high-CO2 world. J. Am. Geophys., 110: C09S09.

Kikkawa, T., Ishimatsu, A., and Kita, J. 2003. Acute CO2 tolerance during the early developmental stages of four marine teleosts. Env. Toxicol., 18: 375–382.

Kikkawa, T., Sata, T., Kita, J., and Ishimatsu, A. 2006. Acute toxicity of temporally varying seawater CO2 conditions on juveniles of Japanese sillago (Sillago japonica). Mar. Poll. Bull., 52: 621–625.

Kurihara H., Shinji, S., and Shirayama, Y. 2004. Effects of raised CO2 on the egg production rate and early development of marine copepods (A.steuri and A. erythraea). Mar. Poll. Bull.,49:721–727.

Langenbuch, M., and Portner, H. O. 2004. High sensitivity to chronically elevated CO2 levels in a eurybathic marine sipunculid. Aquat. Tox., 70: 55–61.

Leggett, W.C. and Deblois, E. 1994. Recruitment in marine fishes - is it regulated by starvation and predation in the egg and larval stages. Netherlands Journal of Sea Research 32: 119-134.

Lett, P. and Kohler, A. 1976. Recruitment: a problem of multi-species interaction and environmental perturbation. J.Fish. Res. Board Can. 33: 1353.

Michaelidis, B., Spring, A., and Portner, H. O. 2007. Effects of long term acclimation to environmental hypercapnia on extracellular acid-base status and metabolic capacity in Mediterranean fish Sparus aurata. Mar. Biol., 150: 1417–1429.

Pepin, P. 1991. Effect of temperature and size on development, mortality and survival rates of the pelagic early life history stages of marine fish. CJFAS 48: 503-518.

Portner, H. O., and Reipschlager, A. 1996. Ocean disposal of anthropogenic CO2: physiological effects on tolerant and intolerant animals. In Ocean Storage of Carbon Dioxide. Workshop 2— Environmental Impact, pp. 57–81. Ed. by B. Ormerod, and M. V. Angel. IEA Greenhouse Gas R&D Programme, Cheltenham, UK.

Portner, H. O., Langebuch, M., and Reipschlager, A. 2004. Biological impact of elevated ocean CO2 concentration: lessons from animal physiology and Earth history. J. Oceanog., 60: 705–718.

Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P., Riebesell, U., Shepherd, J., Turley, C., and Watson, A., 2005, Ocean acidification due to increasing atmospheric carbon dioxide, Policy Document 12/05, Royal Society London.

Principal Investigators

Dr. Simon Nicol
Oceanic Fisheries Programme (OFP)
Secretariat of the Pacific Community (SPC)
98848 Noumea Cedex
Phone (687) 260161
FAX (687) 263818
email: simonn@spc.int

Dr. Dan Margulies
Inter-American Tropical Tuna Commission
8604 La Jolla Shores Drive
La Jolla, CA 92037-1508
Phone (858) 546-7100
FAX (858) 546-7133
email: dmargulies@iattc.org

Dr. Vernon Scholey
Achotines Laboratory
Las Tablas
Provincio Los Santos
Republic of Panama
Phone (507) 995-8166
FAX (507) 995-8282
email: vscholey@iattc.org

Dr. Donald Bromhead
email: donaldb@spc.int
Dr. Simon Hoyle, SPC
email: simonh@spc.int
Ms. Maria Santiago, I-ATTC
email: msantiago@iattc.org
Ms. Jeanne Wexler, I-ATTC
email: jwexler@iattc.org
Dr. Patrick Lehodey, CLS
email: plehodey@cls.fr
Dr. Tatiana Ilyina, U of Hawaii


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