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Reynolds SD, Franklin CE, Norman BM, Richardson AJ, Everett JD, Schoeman DS, White CR, Lawson CL, Pierce SJ, Rohner CA, Bach SS, Comezzi FG, Diamant S, Jaidah MY, Robinson DP, Dwyer RG. Effects of climate warming on energetics and habitat of the world's largest marine ectotherm. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 951:175832. [PMID: 39197762 DOI: 10.1016/j.scitotenv.2024.175832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Revised: 08/23/2024] [Accepted: 08/25/2024] [Indexed: 09/01/2024]
Abstract
Responses of organisms to climate warming are variable and complex. Effects on species distributions are already evident and mean global surface ocean temperatures are likely to warm by up to 4.1 °C by 2100, substantially impacting the physiology and distributions of ectotherms. The largest marine ectotherm, the whale shark Rhincodon typus, broadly prefers sea surface temperatures (SST) ranging from 23 to 30 °C. Whole-species distribution models have projected a poleward range shift under future scenarios of climate change, but these models do not consider intraspecific variation or phenotypic plasticity in thermal limits when modelling species responses, and the impact of climate warming on the energetic requirements of whale sharks is unknown. Using a dataset of 111 whale shark movement tracks from aggregation sites in five countries across the Indian Ocean and the latest Earth-system modelling produced from Coupled Model Intercomparison Project Phase 6 for the Intergovernmental Panel on Climate Change, we examined how SST and total zooplankton biomass, their main food source, may change in the future, and what this means for the energetic balance and extent of suitable habitat for whale sharks. Earth System Models, under three Shared Socioeconomic Pathways (SSPs; SSP1-2.6, SSP3-7.0 and SSP5-8.5), project that by 2100 mean SST in four regions where whale shark aggregations are found will increase by up to 4.9 °C relative to the present, while zooplankton biomass will decrease. This reduction in zooplankton is projected to be accompanied by an increase in the energetic requirements of whale sharks because warmer water temperatures will increase their metabolic rate. We found marked differences in projected changes in the extent of suitable habitat when comparing a whole-species distribution model to one including regional variation. This suggests that the conventional approach of combining data from different regions within a species' distribution could underestimate the amount of local adaptation in populations, although parameterising local models could also suffer from having insufficient data and lead to model mis-specification or highly uncertain estimates. Our study highlights the need for further research into whale shark thermal tolerances and energetics, the complexities involved in projecting species responses to climate change, and the potential importance of considering intraspecific variation when building species distribution models.
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Affiliation(s)
- Samantha D Reynolds
- School of the Environment, The University of Queensland, Brisbane, QLD, Australia; ECOCEAN Inc., 162/3 Powell Rd, Coogee, WA, Australia; Harry Butler Institute, Murdoch University, Murdoch, WA, Australia.
| | - Craig E Franklin
- School of the Environment, The University of Queensland, Brisbane, QLD, Australia
| | - Bradley M Norman
- ECOCEAN Inc., 162/3 Powell Rd, Coogee, WA, Australia; Harry Butler Institute, Murdoch University, Murdoch, WA, Australia
| | - Anthony J Richardson
- School of the Environment, The University of Queensland, Brisbane, QLD, Australia; Centre for Biodiversity and Conservation Science (CBCS), The University of Queensland, Brisbane, QLD, Australia; CSIRO Environment, Queensland Biosciences Precinct, St Lucia, QLD, AUSTRALIA
| | - Jason D Everett
- School of the Environment, The University of Queensland, Brisbane, QLD, Australia; CSIRO Environment, Queensland Biosciences Precinct, St Lucia, QLD, AUSTRALIA; Centre for Marine Science and Innovation, University of New South Wales, Sydney, NSW, Australia
| | - David S Schoeman
- Ocean Futures Research Cluster, School of Science, Technology, and Engineering, University of the Sunshine Coast, Maroochydore, QLD, Australia; Centre for African Conservation Ecology, Department of Zoology, Nelson Mandela University, Gqeberha, South Africa
| | - Craig R White
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton, VIC, Australia
| | - Christopher L Lawson
- School of the Environment, The University of Queensland, Brisbane, QLD, Australia
| | - Simon J Pierce
- Marine Megafauna Foundation, West Palm Beach, FL, USA; School of Science, Technology and Engineering, The University of the Sunshine Coast, Sippy Downs, QLD, Australia
| | | | - Steffen S Bach
- Ramboll, Copenhagen, Denmark; Qatar Whale Shark Research Project, Doha, Qatar
| | - Francesco G Comezzi
- Department of Natural Resources and Environment Tasmania, Marine Resources, Hobart, Tasmania, Australia
| | - Stella Diamant
- Marine Megafauna Foundation, West Palm Beach, FL, USA; Madagascar Whale Shark Project, Nosy Be, Madagascar
| | | | - David P Robinson
- Qatar Whale Shark Research Project, Doha, Qatar; Sundive Research, Byron Bay, New South Wales, Australia
| | - Ross G Dwyer
- School of Science, Technology and Engineering, The University of the Sunshine Coast, Sippy Downs, QLD, Australia
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