Structure of infaunal communities in New Zealand submarine canyons is linked to origins of sediment organic matter

Abstract

Submarine canyons can facilitate the transfer of land-derived organic matter to the deep sea. Here, we investigated links between variability in organic matter availability from land and marine sources and infauna communities in two contrasting canyon systems off New Zealand and used stable isotope analyses to identify potential food sources of benthic invertebrates. Kaik oura Canyon, a steep, short canyon close to the shore, was characterized by high food availability and varying proportions of marine-and land-derived organic matter, whereas Hokitika Canyon, a narrow and lower-gradient canyon that extends further from the coast, was characterized by low food availability and mostly land-derived sediment organic matter throughout. Both macrofaunal and meiofaunal abundance and biomass were greater in Kaik oura Canyon than in Hokitika Canyon. Correlation analyses suggested that land-derived organic matter may contribute to increased meiofaunal abundance in Kaik oura Canyon. Carbon and nitrogen isotopic analyses, however, did not provide unequivocal support for the uptake of land-derived material by large benthic invertebrates in Kaik oura Canyon. Infaunal abundance and biomass were low throughout Hokitika Canyon despite similar concentrations of land-derived organic matter in sediments of both canyons, which suggests that variations in marine-derived organic matter inputs is the main driver of community differences among canyons. Refractory vascular plant material by itself may not provide an adequate food supply to infaunal organisms, but may represent a complementary food resource when more labile marine phytodetritus is also readily available.

Novel Application of a Compound-Specific Stable Isotope (CSSI) Tracking Technique Demonstrates Connectivity Between Terrestrial and Deep-Sea Ecosystems via Submarine Canyons

“…In addition to potentially changing the rate of carbon sequestration by the deep-sea, shifts in the magnitude of terrestrial carbon transport may also have implications for food webs. Leduc et al (2020) provide evidence supporting a trophic link between terrestrial organic matter and benthic communities in Kaikōura Canyon. Therefore, decreased land-to-ocean subsidies could reduce the productivity of this unique ecosystem (De Leo et al, 2010).…”

“…As we have identified earlier, a variety of processes are likely to be involved in determining which river(s) contribute most of the terrestrial organic matter transported to the deep-sea. Regardless of which mechanism(s) are involved, the transport of organic matter to the deep is likely to have two main consequences, namely: (1) an impact on secondary productivity through the provision of an additional food source to benthic animals (see companion paper by Leduc et al, 2020) and (2) providing a significant carbon sink through the transfer, burial and sequestration of relatively refractory terrestrial carbon to the deep seabed.…”

“…The aim of the present study was to investigate the quantity, quality and sources of the organic matter in two contrasting canyons, while a companion study examined the relationships between sediment organic matter parameters and macroand meiofaunal abundance, biomass and community structure (Leduc et al, 2020).…”

“…fromLeduc et al (2020). Values were obtained from one sample per site, except for isotopic data at Hokitika Canyon sites where N = 3 and mean and standard deviation values are provided.…”

The Depleted Carbon Isotopic Signature of Nematodes and Harpacticoids and Their Place in Carbon Processing in Fish Farm Sediments

“…The impact of fish farming activities on the energy transfer toward the receiving meiofauna community, however, is far from well known. To define carbon fluxes in marine ecosystems ecologists use natural isotopic signatures (Fry, 2006;Callier et al, 2013;Leduc et al, 2020) which can be combined with the uptake of pre-labeled food in incubation experiments (Middelburg et al, 2000;Carman and Fry, 2002;De Troch et al, 2007). About 1-2 of 13 C enrichment is mostly observed per trophic level through the marine food web (DeNiro and Epstein, 1981;Ostrom and Fry, 1993;Soreide et al, 2006).…”