This study investigates the deep‐sea food‐web at the South Sandwich Islands in the Southern Ocean, focusing on how net primary production drives interannual changes in food chain length and overall ecosystem structure.

The researchers used stable isotope analyses (δ¹³C and δ¹⁵N) from the muscle tissues of various species collected during fishing seasons in 2020, 2021, and 2022. They identified a food-web with five main trophic levels, with Patagonian (Dissostichus eleginoides) and Antarctic (D. mawsoni) toothfishes as the top predators and noted a potential sixth level when including predators such as seals and whales (Figure 1).

The study found that food chain length varied between years, with the longest chain recorded in 2020 and a shortening of about 0.30 trophic levels by 2022. These changes were linked to shifts in the isotopic signatures of species across multiple trophic levels, suggesting that even mid-trophic level organisms showed significant variability over time.

A major finding is the strong positive linear relationship between food chain length and net primary production. Years with higher net primary production (and related parameters like chlorophyll a concentration) were associated with longer food chains. This supports the productivity hypothesis, which suggests that more productive systems can support a longer chain of energy transfer through more trophic levels. The research highlights the importance of interactions between pelagic (open water) and benthic/demersal (seafloor) components. This coupling occurs primarily between the third and fourth trophic levels, where mobile pelagic species (like squids and crustaceans) interact with demersal fish. Such coupling is key for energy and nutrient fluxes between different ecosystem compartments.

The authors suggest that as climate change increases productivity in the Southern Ocean, food webs may become longer. This has important implications for energy transfer efficiency, exposure to contaminants (due to biomagnification), and alterations in nutrient cycling, potentially affecting the entire ecosystem’s structure and function.

Overall, the paper demonstrates that deep‐sea food-web structure at the South Sandwich Islands is dynamic and strongly influenced by variations in net primary production. These findings provide crucial insights into how climate-driven changes in productivity could reshape trophic interactions and energy flow in one of the world’s most remote marine ecosystems.

Source: Queirós, J. P., Hollyman, P. R., Bustamante, P., Vaz, D., Belchier, M., & Xavier, J. C. (2025). Deep‐sea food‐web structure at South Sandwich Islands (Southern Ocean): net primary production as a main driver for interannual changes. Ecography.

Author: Sara Santos