Influence of Deep-Water Corals and Sponge Gardens on Infaunal Community Composition and Ecosystem Functioning in the Eastern Canadian Arctic

Marie Pierrejean,F Guillaume Blanchet,Cindy Grant,Frédéric Maps,Gwénaëlle Chaillou,Christian Nozais,Philippe Archambault,Bárbara De Moura Neves,Evan Edinger

doi:10.3389/fmars.2020.00495

Abstract

The relationships between infaunal diversity and ecosystem function of biogenic structures in the Eastern Canadian Arctic remain poorly documented. Our study investigated the influence of sponge gardens at the Frobisher Bay site (138 m) and bamboo corals at the Baffin Bay site (1007 m) on the infaunal community structure and benthic ecosystem functioning. The occurrence of both types of biogenic structure type enhanced particular taxa and/or feeding guilds. A large density of suspension filter feeders was observed in bamboo coral sediment, whereas bare sediment exhibited a large proportion of nematodes and deposit-detritus feeders. Sponge gardens’ sediment showed a high proportion of isopods, Paraonidae polychaetes and up/down conveyors whereas bare sediment exhibited a large density of filter feeders. Through incubation cores, we measured ex-situ benthic nutrient and oxygen fluxes at the sediment-water interface in each habitat and site. Biogeochemical fluxes varied significantly between habitats in the Baffin Bay site with a significant impact of bamboo coral habitat on nutrient fluxes (nitrate, ammonium and silicate). Surprisingly, the sediment hosting bamboo corals acted as a source of nitrate and ammonium reaching values similar or higher to the Frobisher site despite the difference in water depth, and thus food supply between the two sites. These significant releases could derive from (i) a high organic matter deposition in bamboo coral habitat, allowed by their erected structure, (ii) a high efficiency of bioturbators (surficial modifiers and burrowers) mixing the surface layer of the sediment and (iii) the difference in sediment type. Our study highlighted that, compared to its adjacent habitat, the presence of bamboo corals appeared to enhance the infaunal density and nutrient release of its sediment. In contrast, the impact of sponge gardens was not as clear as for bamboo coral habitat, likely due to the relatively significant presence of megabiota in the sponge garden adjacent habitat. Thus, our results based on a relatively small sample size, indicate that the bamboo coral habitat seems to increase the efficiency of deep-benthic ecosystem functioning, while that of sponge garden on the shallow ecosystem functioning remains uncertain.

Highlights

Three-dimensional biogenic structures, designated as marine animal forests, are composed primarily of ecosystem engineering species such as sponges, cnidarians, bryozoans, ascidians and other sessile benthic organisms (Gili and Coma, 1998; Rossi et al, 2012)
We addressed our objectives by exploring the following research questions: (i) are the taxonomic and functional diversities of infaunal communities similar in bare sediment and biogenic structure sediment?; (ii) do biogeochemical fluxes at the sedimentwater interface vary spatially according to the nature of the habitat?; and (iii) which environmental and biological variables explain biogeochemical fluxes in these habitats?
Near-bottom water temperature at the study sites varied between −1.2 and 0.7◦C, in the Frobisher Bay (FB) and Baffin Bay (BB) sites, respectively (Table 2)

Summary

Introduction

Three-dimensional biogenic structures, designated as marine animal forests, are composed primarily of ecosystem engineering species such as sponges, cnidarians, bryozoans, ascidians and other sessile benthic organisms (Gili and Coma, 1998; Rossi et al, 2012). Habitat heterogeneity resulting from these structures represents one of the main factors that influences the distribution of biodiversity at both local and regional spatial scales (Levin et al, 2001; Buhl-Mortensen et al, 2010). The main factor driving this biodiversity gain in biogenic habitats is derived, in part, from their erected structure. Sponges may influence the water column by consuming dissolved oxygen by respiration (Bell, 2008) filtering and catching particles for food supply (e.g., dissolved organic carbon; Yahel et al, 2003) and altering nutrient cycling (i.e., silicate and nitrogen; Bell, 2008)

Methods

Results

Discussion

Conclusion