The influence of the cape canyon on the food web structure of the southern Benguela upwelling system

Abstract

Submarine canyons are heterogeneous environments known to support a variety of benthic organisms and they are considered biodiversity hotspots. The peculiar hydrographic conditions that characterize these systems, including the high level of organic matter accumulation and transport, can lead to intense resuspension that can influence the food available to the benthos. The Cape Canyon is the largest South African canyon located off the western margin of the country. It has a unique structure that connects the coastline to deep-sea environments, and it is also extremely productive being under the influence of upwelling. Here we aim to characterize the role of hydrography in influencing the food availability to the benthos, comparing stations within the Cape Canyon and from adjacent areas. Samples were collected in March 2017 and data were acquired to describe the physical environment (temperature, salinity, oxygen) in relation to the benthic invertebrate specimens used for stable isotope analyses. The δ¹⁵N of suspended particulate matter (SPM) did not vary between canyon and non-canyon regions, but it increased with depth, most likely as the result of particle bacterial remineralization. In contrast, the δ¹³C_SPM changed as a function of canyon. Such effects were only partially reflected in the δ¹⁵N and δ¹³C of the trophic groups identified, which generally did not vary between canyon and non-canyon stations. This information increases our understanding of the ecological function of the benthos in and around the Cape Canyon, which is essential for the ongoing marine spatial planning efforts.