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

Abstract

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.

Food web structure and species’ role in an oceanic Marine Protected Area in the subantarctic

“…The presence of these mid-trophic level species in the community in uences the way it responds to disturbances, affecting its resilience, robustness and vulnerability. This suggest that the MPAY is a WW ecosystem, supporting the 'wasp-waist' control hypothesis described by and proposed to dominate at the southwestern South Atlantic Ocean (e.g., Padovani et al, 2012;Arkhipkin and Laptikhovsky, 2013;Saporiti et al, 2015;Büring et al, 2024). An aspect to consider is that, due to the physical characteristics of the MPAY (bathymetry, currents and sea fronts that in uence it, etc.…”

“…Regarding to cephalopods, the Patagonian squid, the only species of Doryteuthis found in the Southern Atlantic Ocean (Büring, 2023), and one of the main components of marine food webs linking primary consumers and marine top predators (Coll et al, 2013;Gasalla et al, 2010;Navarro et al, 2013), ranked sixth at KSI ranking. This species has recently been identi ed as an abundant mid-trophic species that plays an important role in the Malvinas/Falkland shelf ecosystem that also exhibits a WW control (Büring et al, 2024).…”