Time-Dynamic Food Web Modeling to Explore Environmental Drivers of Ecosystem Change on the Kerguelen Plateau

Abstract

Understanding the impacts of climate and fishing on marine systems is important for ecosystem-based management in the Southern Ocean, but can be difficult to evaluate due to patchy data in space and time. We developed the first time-dynamic food web model for the Kerguelen Plateau using Ecopath with Ecosim to explore likely drivers of change in this relatively data-poor region. The Kerguelen Plateau is located at the centre of intersecting frontal systems and is inhabited by one of the largest populations of the commercially important Patagonian toothfish. We used this model to evaluate the environmental and human drivers of food web dynamics in the region by calibrating it with French and Australian fisheries data from 1997-2018 and biomass data for the period 1986-2018. Fishing was not identified as a driver of food web dynamics within this model, which could indicate that current management strategies are sustainable. A correlation analysis with environmental parameters likely to drive food web dynamics (sea surface temperature, zonal wind, Southern Annular Mode and chlorophyll a concentration) highlighted cool sea surface temperature, higher zonal wind speeds and negative phases of the Southern Annular Mode as important drivers of change, particularly during the summer. As the Southern Ocean is predicted to warm and winds are expected to intensify under future climate change, our study illustrates the importance of considering environmental change in ecosystem management.

Albatrosses respond adaptively to climate variability by changing variance in a foraging trait

“…While traditionally associated with warmer SST and lower productivity in the eastern tropical Pacific, studies have shown that climatic effects of El Niño are complex and often lead to cooler waters in other regions around the globe (Hermes & Reason, 2005; Reason et al, 2000; Subramaniam et al, 2020). For example, some areas exhibit colder SST and/or higher productivity in El Niño years, whereas others show lagged effects to El Niño‐associated cooling, often linked to bathymetric features and front locations.…”

Productivity and Change in Fish and Squid in the Southern Ocean

“…Recently, productivity of Patagonian toothfish on the Kerguelen Plateau has been related to oceanographic conditions, where prey availability may decrease because of increased variability in these conditions in coming years (Subramaniam et al, 2020). This has also been suggested for icefish populations that prey on krill (Reid, 2019), for which the area of greatest productivity is expected to move south (Johnston et al, under review).…”

Southern Ocean Food Web Modelling: Progress, Prognoses, and Future Priorities for Research and Policy Makers

“…Several studies have used Ecosim to explore the timedynamic variations of Southern Ocean food webs (Surma et al, 2014;Suprenand and Ainsworth, 2017;Dahood et al, 2019;Subramaniam et al, 2020b). This approach fits models from Ecopath to time-series and/or fisheries data for functional groups (Christensen et al, 2008).…”