WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2024 27 time of spawning, egg development, hatching success, and development of firstfeeding larvae were described by Margulies et al. (2007b) and Guillen et al. (2014). No spawning was observed at temperatures higher than 29.7 °C, and the time of day at which YFT spawned was strongly, positively correlated with water temperature (Margulies et al. 2007b). This adaptive response of the YFT in their diel pattern of spawning, and consequently, time of hatching, has important significance for the early life history of YFT, especially in a scenario where sea surface temperatures are predicted to increase from 1-4° C by 2100 (IPCC 2021). YFT feeding larvae inhabit the upper strata of the ocean’s mixed layers, and most likely will feel the impacts of global warming more than adults. To determine possible effects of ocean warming on larvae, studies investigating the upper water temperature limits for growth and survival of YFT larvae during the first 2 weeks of life, and comparative studies with PBF larvae, are planned in 2024 and 2025. The effects of ocean acidification on eggs, yolk-sac larvae and first-feeding larvae of YFT were also studied experimentally at the Achotines Laboratory (Bromhead et al. 2015, Frommel et al. 2016, Heuer et al. 2020, 2023, Wexler et al. 2023). The experimental results were combined to estimate the effects of ocean acidification and global warming through the ecosystem model SEAPODYM to project yellowfin population changes in the Pacific Ocean (Nicol et al. 2022). Studies were conducted in 2011 at the Achotines Laboratory investigating the effects of acidification at levels that are predicted to occur in parts of the Pacific Ocean in the next 100 to 300 years, and quantifying these effects on egg, yolk-sac, and first-feeding larval stages of YFT. Results indicated that projected near-term (out to Year 2100) acidification levels (pH 7.6-7.8) have the potential for significantly reducing survival and size of larvae, as well as prolonging egg timeto-hatch (Bromhead et al. 2015, Figure 7). Histological analysis indicated significant physiological effects such as organ damage observed in the liver, pancreas and kidney of YFT larvae (Frommel et al. 2016), and this could impair survival and growth beyond the developmental phases observed in the study, contributing to cumulative mortality. Nicol et al. (2022), in a modeling study utilizing the experimental results from 2011, predicted that the effects of global warming will most likely be stronger than the effects of ocean acidification on YFT population dynamics, and predicted an eastward shift in the distribution of YFT in the Pacific Ocean. However, acidification was also projected to weaken the magnitude of increase in YFT abundance in the Eastern Pacific. Sub-lethal or cumulative organ damage in YFT larvae resulting from ocean acidification is an important factor to consider when projecting population dynamics. It remains unclear whether tuna possess the capacity to adapt to acidification through selection, and if resistant individual traits would be heritable (Margulies et al. 2016, Nicol et al. 2022). Other Research Topics Numerous collaborative studies have been conducted with different institutions from all over the world during four decades of research at the Achotines Laboratory. Collaborative studies have been conducted with 18 U.S. universities, 14 international universities, and 38 governmental, NGO, or private research organizations (Margulies, personal communication). The collaborative projects have included an annual Tuna and Pelagics Workshop, with the Graduate Aquaculture Program of the University of Miami, USA, since 2003. Students, researchers, FIGURE 9. The ELHG of IATTC. Upper picture from the left: Susana Cusatti, Yole Buchalla and Daniel Margulies. Bottom left: Eblin Pereira and Vernon Scholey. The effects on marine biodiversity caused by climate change, including ocean warming, ice-melting, marine heatwaves, and ocean acidification, currently affects an estimated 680 million people living in low-lying coastal areas, almost 2 billion who live in coastal megacities, nearly half of the world’s population that depends on fish for protein, and almost 60 million who work in fisheries and aquaculture sectors worldwide (UN 2024). (CONTINUED ON PAGE 28)
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