Factors affecting trophic compositions of offshore benthic invertebrates at a sub‐Antarctic archipelago

Abstract

Food availability is a key regulator of the distribution, metabolism, and success of benthic populations. In deep sea ecosystems, hydrodynamics and depth play fundamental roles in determining benthic food resources. Recent studies suggest that the Southern Ocean sub‐Antarctic front is shifting southward, with implications for primary production and food availability around the sub‐Antarctic Islands embedded in the Antarctic Circumpolar Current. We used fatty acid (FA) and stable isotope (SI) analyses to investigate the trophic pattern of benthic invertebrates and suspended particulate matter (SPM) at three Depths (shallow: 100 m, middle: 300 m, and deep: 600 m) in three hydrographic regions with different flow and productivity regimes around the Prince Edward Islands. Both region and depth affected the SI values of SPM, while feeding guild was the key factor influencing consumer trophic values. Depth affected the δ15N of all trophic groups and the FA compositions of suspension feeders. Deeper samples had a higher δ15N and showed a greater proportion of mono‐ and saturated fatty acids, reflecting greater remineralization of SPM and of food reaching the seafloor. Region affected the δ13C and FA values of SPM, suspension feeders and deposit feeder/scavengers, with differences between the interisland and open ocean regions. This was probably linked to the retention of nutrients and phytoplankton between the islands. Critically, the effects of depth and hydrographic region were taxon specific, indicating that long‐term responses to environmental change may have complex consequences for the feeding ecology and viability of benthic populations, with implications for the higher trophic levels that these populations support.

Plankton community composition and productivity near the Subantarctic Prince Edward Islands archipelago in autumn

“…A climate-driven shift towards a plankton ecosystem dominated by temperate zooplankton species has implications for the entire archipelago food web. For example, changes observed in the ecology and composition of the benthic community at Prince Edward Islands over the last three decades have been attributed to changes in food source(s) linked to the plankton (von der Meden et al 2017;Puccinelli et al 2018).…”

Influence of spatial and temporal variation on establishing stable isotope baselines of δ15N, δ13C, and δ34S in a large freshwater lake

“…Nitrogen isotope values (δ 15 N) can be elevated as a result of urban and agricultural run-off (Diebel & vander Zanden, 2009), but if that was the cause of the observed differences between basins, the western basin should have had higher δ 15 N since it has the highest influence of both in comparison to the rest of the lake (Watson et al, 2016). Increasing water depth has been shown to elevate δ 15 N and δ 13 C in lower trophic level organisms in marine systems (Puccinelli et al, 2018), and evidence of this relationship has been observed in large freshwater systems, such as Mysis in Lake Ontario (Johannsson et al, 2001). Consequently, depth could be a factor contributing to the spatial trends observed in δ 15 N and δ 34 S; however, we do not have sufficient data to state this con- 3 ), and spatial heterogeneity of the phytoplankton community due to basin differences in nutrient availability (Leggett et al, 2000;Syväranta et al, 2008).…”

Benthic species patterns in and around the Cape Canyon: A large submarine canyon off the western passive margin of South Africa

“…The latter consequently represents a higher feeding method to species ratio. It is however worth noting that the mode categorizations were adopted from a range of sources (MacDonald et al, 2010;Demopoulos et al, 2017;Puccinelli et al, 2018; O'Hara, pers comm; Marine Species Traits editorial Frontiers in Marine Science frontiersin.org board, 2022) which may not be a true reflection of local feeding patterns. Nonetheless, converging presence of suspension feeders noted in both canyon (ophiuroids, holothuroids, and bryozoans) and non-canyon stations (one octocoral and a polychaete) may be driven by the overall upwelling conditions of the Benguela region.…”