Unveiling the wasp-waist structure of the Falkland shelf ecosystem: the role of Doryteuthis gahi as a keystone species and its trophic influences

• Published in: Journal of the Marine Biological Association of the United Kingdom 2024-02, Vol.104, Article e2
• Main Authors: Büring, Tobias, van Der Grient, Jesse, Pierce, Graham, Bustamante, Paco, Scotti, Marco, Jones, Jessica B., Rocha, Francisco, Arkhipkin, Alexander
• Format: Article
• Language: English
• Subjects: Animal biology; Biodiversity and Ecology; Biomass; Cohorts; Doryteuthis gahi; Earth Sciences; Ecology, environment; Ecosystems; Energy flow; Environmental Sciences; Feeding; Fisheries management; Fishing; Food chains; Food webs; Functional groups; Impact prediction; Invertebrate Zoology; Isotopes; Keystone species; Life Sciences; Marine ecosystems; Marine molluscs; Ocean circulation; Oceanography; Predators; Sciences of the Universe; Shelving; Stable isotopes; Trophic levels; Trophic relationships; Trophic structure; Upwelling
• ISSN: 0025-3154; 1469-7769
• DOI: 10.1017/S0025315423000887

The Falkland Shelf is a highly productive ecosystem in the Southwest Atlantic Ocean. It is characterized by upwelling oceanographic dynamics and displays a wasp-waist structure, with few intermediate trophic-level species and many top predators that migrate on the shelf for feeding. One of these resident intermediate trophic-level species, the Patagonian longfin-squid Doryteuthis gahi, is abundant and plays an important role in the ecosystem. We used two methods to estimate the trophic structure of the Falkland Shelf food web, focusing on the trophic niche of D. gahi and its impacts on other species and functional groups to highlight the importance of D. gahi in the ecosystem. First, stable isotope measurements served to calculate trophic levels based on an established nitrogen baseline. Second, an Ecopath model was built to corroborate trophic levels derived from stable isotopes and inform about trophic interactions of D. gahi with other functional groups. The results of both methods placed D. gahi in the centre of the ecosystem with a trophic level of ~ 3. The Ecopath model predicted high impacts and therefore a high keystoneness for both seasonal cohorts of D. gahi. Our results show that the Falkland Shelf is not only controlled by species feeding at the top and the bottom of the trophic chain. The importance of species feeding at the third trophic level (e.g. D. gahi and Patagonotothen ramsayi) and observed architecture of energy flows confirm the ecosystem's wasp-waist structure with middle-out control mechanisms at play.