title: Stable isotope and signature fatty acid analyses suggest reef manta rays feed on demersal zooplankton.
abstract: Assessing the trophic role and interaction of an animal is key to understanding its general ecology and dynamics. Conventional techniques used to elucidate diet, such as stomach content analysis, are not suitable for large threatened marine species. Non-lethal sampling combined with biochemical methods provides a practical alternative for investigating the feeding ecology of these species. Stable isotope and signature fatty acid analyses of muscle tissue were used for the first time to examine assimilated diet of the reef manta ray Manta alfredi, and were compared with different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). Stable isotope δ(15)N values confirmed that the reef manta ray is a secondary consumer. This species had relatively high levels of docosahexaenoic acid (DHA) indicating a flagellate-based food source in the diet, which likely reflects feeding on DHA-rich near-surface and epipelagic zooplankton. However, high levels of ω6 polyunsaturated fatty acids and slightly enriched δ(13)C values in reef manta ray tissue suggest that they do not feed solely on pelagic zooplankton, but rather obtain part of their diet from another origin. The closest match was with demersal zooplankton, suggesting it is an important component of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to the horizontal and vertical movement patterns of this giant planktivore. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs.
authors.affiliation: School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia ; Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research, Dutton Park, Queensland, Australia.
authors.forename: Lydie I E
authors.initials: LI
authors.lastname: Couturier
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Rohner
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Richardson
authors.forename: Andrea D
authors.initials: AD
authors.lastname: Marshall
authors.forename: Fabrice R A
authors.initials: FR
authors.lastname: Jaine
authors.forename: Michael B
authors.initials: MB
authors.lastname: Bennett
authors.forename: Kathy A
authors.initials: KA
authors.lastname: Townsend
authors.forename: Scarla J
authors.initials: SJ
authors.lastname: Weeks
authors.forename: Peter D
authors.initials: PD
authors.lastname: Nichols
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis; D018940:Elasmobranchii / Q000502:physiology*; D043371:Fatty Acids, Omega-6 / Q000032:analysis / Q000378:metabolism*; D005247:Feeding Behavior / Q000502:physiology*; D009587:Nitrogen Isotopes / Q000032:analysis; D015048:Zooplankton
chemical_list: D002247:Carbon Isotopes; D043371:Fatty Acids, Omega-6; D009587:Nitrogen Isotopes