Increased Mortality, Organ Damage and Variable Expression of Alleles in Yellowfin Tuna Larvae under ocean acidification

Chair: Tommy Moore

Jane Wiliamson (1)*, Don Bromhead (2), Andrea Frommel (3), Michael Gillings (1), Jon Havenhand (3), Simon Hoyle (2), Tatiana Ilyina (4), Patrick Lehodey (5), Cleridy Lennert-Cody (6), Daniel Marguiles (6), Simon Nicol (2), Vernon Scholey (6), Maria Stein (6), Liette Vandine (1), Jeanne Wexler (6)

1 Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia
2 Secretariat of the Pacific Community, BP D5 Noumea, New Caledonia
3 Department of Marine Science, Tjärnö, University of Gothenburg, 45296, Sweden
4 Max Planck Institute for Meteorology, Bundesstr. 53, D-20146 Hamburg, Germany
5 Collecte Localisation Satellites, Space Oceanography Division, 31520 Ramonville Saint-Agne, France
6 Inter-American Tropical Tuna Commission, 8901 La Jolla Shores Drive, La Jolla, CA 92037-1509 USA

Background
The majority of ocean acidification (OA) studies involving fish have focused on survival, growth and behavioural responses in coastal or reef species. OA can affect these fishes by disrupting physiological processes, and impairing neurological and behavioural responses. It is not known if OA will have similar impacts on pelagic predators inhabiting the open ocean. Yellowfin Tuna, Thunnus albacares, are widely dispersed top predators in pelagic ecosystems. In the Pacific Ocean, they form the basis of one of the largest and most valuable fisheries globally. This research assesses the impact of OA on survival, organ damage and differential gene expression on eggs and larvae of Yellowfin Tuna.

Methods
Experiments were done at the Inter-American Tropical Tuna Commission’s tuna breeding hatchery in Panama. Eggs and larvae were exposed to levels of OA projected to occur in their spawning habitat in near and far future IPCC scenarios. Survival of individuals, along with their morphometric data, was assessed throughout the experiment. Samples were also assessed for vial organ development and for genetic analysis.

Findings
We found lowered rates of survival and larval growth at greater levels of OA, which correlated closely with histological observations of progressive degradation of vital organs. Using genetic techniques we also showed variable expression of alleles in several of the 8 optimised loci that corresponded to increases in OA. These may indicate rapid selection of OA-tolerant individuals.

Conclusions
Substantial changes occurred in the early life history stages of yellowfin tuna in response to OA in our laboratory experiment. While it should be noted that this was an exploratory experiment looking at a small part of the life history of a longer-lived organism, our results show that OA does have the potential to impact on pelagic predators such as tuna.