Fish larvae have complex strategies to cope with thermal and hypoxic stress
The United Nations declared 2021-2030 as the Decade of Ocean Science for Sustainable Development, underscoring the integral role of science-based ocean management in meeting sustainable development goals. Among the many facets of this is understanding the response of fish larvae to climate change. With the support of the Marie Skłodowska-Curie Actions (MSCA) programme, the FUTURELARVAE project investigated the single and combined effects of ocean warming and oxygen depletion on larval distribution patterns, critically integrating physiological and behavioural responses that might mediate any changes.
Filling knowledge gaps with experiments and new models
Species distribution models are widely used to assess the suitability of spawning and recruitment habitats of fish larvae. However, according to MSCA fellow André R. A. Lima of ISPA CRL University Institute: “Only a handful of articles on the topic have forecast the impact of climate change on larval distribution. Furthermore, these projections have not included the full range of processes that shape larval distribution in different scenarios of climate change.” FUTURELARVAE addressed both these issues in a combined experimental and modelling campaign.
Two species, two different natural distributions
Lima chose to study two broadcast spawners – fish that release many eggs and sperm into the open sea for external fertilisation – with slightly different developmental journeys. The early life of broadcast spawners is known as the pelagic drift phase. The white seabream has a longer drift phase than the sand smelt before coming closer to coastlines. The team studied the fish larvae after a few weeks of dispersal. At this point, the larvae have some swimming capacity and move from the open sea to settle in coastal habitats where they experience the consequences of warming and hypoxia. “These species have evolved different successful life history strategies to spawn at specific times and in certain regions where environmental conditions are optimal to guarantee the successful recruitment of fish larvae to adult populations. It is necessary to compare and understand whether these strategies will be successful in future marine habitats,” explains Lima.
Climate change, physiological responses and larval distribution
Lima’s novel data and improved species distribution model delivered encouraging results. White seabream larvae are able to improve their anaerobic metabolism to increase swimming speed, even when the aerobic metabolism is reduced under the single and combined effects of ocean warming and oxygen depletion. Sand smelt larvae are able to reduce mobility to stabilise their metabolism when exposed to the same stressors. “We did not expect the sensitive larval phase to have complex coping strategies to acclimate under thermal and hypoxic stress. By integrating multiple responses of ecological relevance, we were able to identify the relationships between physiological and behavioural strategies and unravel the mechanisms used by early fish stages to cope with combined warming and hypoxia. However, the ecological costs of these strategies need to be addressed,” Lima concludes. Information about future spawning habitats, the recruitment of fish larvae to adult populations and range expansion or habitat loss, as well as the identification of so-called climate refugia will support the conservation and management of fisheries resources. FUTURELARVAE has made a significant contribution to this and met the Ocean Decade’s call for “the science we need for the ocean we want”.
Keywords
FUTURELARVAE, fish, fish larvae, climate change, larval distribution, species distribution model, ocean warming, oxygen depletion, broadcast spawners, sand smelt, seabream
