Horizontal and vertical food web structure drives trace element trophic transfer in Terra Nova Bay, Antarctica

Abstract

Despite in the last decades a vast amount of literature has focused on trace element (TE) contamination in Antarctica, the assessment of the main pathways driving TE transfer to the biota is still an overlooked issue. This limits the ability to predict how variations in sea-ice dynamics and productivity due to climate change will affect TE allocation in food webs. Here, food web structure of Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica) was first characterised using carbon and nitrogen stable isotopes (δ 13 C, δ 15 N) of organic matter sources (sediment and planktonic, benthic and sympagic primary producers) and consumers (zooplankton, benthic invertebrates and vertebrates). Then, relationships between TEs (Cd, Cr, Co, Cu, Hg, Ni, Pb and V) and stable isotopes were assessed in order to evaluate if and how horizontal (organic matter pathways) and vertical (trophic position) food web features influence TE transfer to the biota. Regressions between log[TE] and δ 13 C revealed that the sympagic pathway drives accumulation of V in primary consumers and of Cd and Hg in secondary consumers, and that a coupled benthic/planktonic pathway drives Pb transfer to all consumers. Regressions between log[TE] and δ 15 N showed that only Hg biomagnifies across trophic levels, while all the others TEs showed a biodilution pattern, consistent with patterns observed in temperate food webs. Although the Cd behavior needs further investigations, the present findings provide new insights about the role of basal sources in the transfer of TEs in polar systems, especially important nowadays in light of the forecasted trophic changes potentially resulting from future climate change-induced modification of sea-ice dynamics.Capsule : Depiction of trace element transfer in the Antarctic food web highlighted an important role of both sympagic and phytoplanktonic pathways, suggesting that forecasted modification of sea-ice dynamics due to climate change may alter contaminant accumulation and biomagnification patterns.

Antarctic food web architecture under varying dynamics of sea ice cover

“…Lastly, a Mantel test was applied to assess if isotopic signatures of ITUs were predictive of the feeding links they made in the food web, considering both the identity and the relative contribution of each food source to each ITU. The Mantel test, as a permutation test for correlation between two distance or similarity matrices, allowed us to compare multivariate data with different similarity measures 79 . Here, the Euclidean distance and the Bray-Curtis dissimilarity were selected to quantify isotopic distances between ITUs and pairwise differences in feeding links respectively 72,79 .…”

Nitrogen and metal pollution in the southern Caspian Sea: a multiple approach to bioassessment

“…In order to deepen the knowledge of the source, diffusion, and effects of pollution in the Caspian Sea, future studies on this complex ecosystem should explicitly consider the spatial variability of anthropogenic pressures and the land use cover. Furthermore, as already observed in the Caspian Sea (Agah et al 2007) and in other coastal ecosystems (Signa et al 2019), the potential harmful effects of metal pollution on higher trophic levels should be further investigated. Therefore, for a highly anthropized ecosystem such as the Iranian Caspian Sea, determining the effects of metal and nutrient pollution on the food web is necessary for effective management and conservation actions.…”

“…This result was expected, as macroalgae absorb metals from water (Bonanno and Orlando-Bonaca 2018), while sediments represent the long-term repository in aquatic environments. The absence of correlation also indicates a divergent partitioning of metals from water to these two basal compartments of the food web and possibly implies different effects of the herbivore and detrital energy pathways on the transfer of metals to upper trophic levels (Mendoza-Carranza et al 2016;Signa et al 2019).…”

Seasonal Food Web Dynamics in the Antarctic Benthos of Tethys Bay (Ross Sea): Implications for Biodiversity Persistence Under Different Seasonal Sea-Ice Coverage

“…Studies in the Ross Sea have demonstrated that sympagic production is readily incorporated into benthic biomass following sea-ice break-up (Norkko et al, 2007;Calizza et al, 2018), supporting between 30 and 80% of benthic secondary production (Wing et al, 2018). Accordingly, pulsed sympagic inputs during summer (Pusceddu et al, 2000(Pusceddu et al, , 2009 produce significant changes in the diet and trophic position of benthic taxa (Norkko et al, 2007;Calizza et al, 2018;Wing et al, 2018;Rossi et al, 2019), with cascade effects on predators at higher trophic levels (Leu et al, 2015;Poloczanska et al, 2016) and contaminant redistribution throughout the food web (Signa et al, 2019).…”