Recycling pathways in cold-water coral reefs: Use of dissolved organic matter and bacteria by key suspension feeding taxa

Sandra R Maier,Raymond J Bannister,Peter Van Breugel,James Kar-Hei Fang,Dick Van Oevelen,Pieter Van Rijswijk,Tina Kutti

doi:10.1038/s41598-020-66463-2

Abstract

Cold-water coral (CWC) reefs are one of the most diverse and productive ecosystems in the deep sea. Especially in periods of seasonally-reduced phytodetritus food supply, their high productivity may depend on the recycling of resources produced on the reef, such as dissolved organic matter (DOM) and bacteria. Here, we demonstrate that abundant suspension feeders Geodia barretti (high-microbial-abundance sponge), Mycale lingua (low-microbial-abundance sponge) and Acesta excavata (bivalve) are able to utilize 13C-enriched (diatom-derived) DOM and bacteria for tissue growth and respiration. While DOM was an important potential resource for all taxa, utilization of bacteria was higher for the sponges as compared to the bivalve, indicating a particle-size differentiation among the investigated suspension feeders. Interestingly, all taxa released 13C-enriched particulate organic carbon, which in turn may feed the detritus pathway on the reef. Especially A. excavata produced abundant (pseudo-)fecal droppings. A second stable-isotope tracer experiment revealed that detritivorous ophiuroids utilized these droppings. The high resource flexibility of dominant reef suspension feeders, and the efficient recycling of their waste products by the detritivore community, may provide important pathways to maintain the high productivity on cold-water coral reefs, especially in periods of low external food supply.

Highlights

Cold-water coral (CWC) reefs are one of the most diverse and productive ecosystems in the deep sea
In stable isotope tracer experiment 1 (Fig. 2a), we studied the utilization of two substrates, 13C-enriched dissolved organic matter (DOM) and 13C-enriched bacteria by abundant CWC reef suspension feeders
To the HMA sponge G. barretti, the LMA sponge M. lingua and the bivalve A. excavata were chosen for this study, to (1) test the original hypothesis that HMA sponges, with their high abundance of microbes, are better-suited for DOM acquisition compared to other suspension feeders[21,23,24], and (2) investigate whether bivalves, like sponges, can utilize bacteria as resource

Summary

Introduction

Cold-water coral (CWC) reefs are one of the most diverse and productive ecosystems in the deep sea. Mycale lingua colonizes the live coral framework[15], G. barretti lives on the dead reef framework or in sponge grounds neighbouring the reefs, and A. excavata forms clusters within grooves or beneath overhangs of the reef framework[15] With their high water processing rates[16,17], these active suspension feeders may readily access resources such as DOM and bacteria. In stable isotope tracer experiment 1 (Fig. 2a), we studied the utilization of two substrates, 13C-enriched DOM (diatom-derived for logistical constraints, as explained below) and 13C-enriched bacteria by abundant CWC reef suspension feeders. During the preparatory and experimental phase, we observed a high production of (pseudo-)fecal droppings by A. excavata, which we considered as potential substrate for reef detritivores (Fig. 1a) This hypothesis was tested in a second stable isotope tracer experiment This hypothesis was tested in a second stable isotope tracer experiment (Figs. 1b, 2b), in which we followed the isotope-tracer 13C through an ‘experimental food chain’, consisting of artificially 13C-enriched diatoms (Skeletonema marinoi), A. excavata fed with the diatoms, its (pseudo-) fecal droppings, and the tissue of reef ophiuroids fed with the bivalve droppings

Methods

Results

Conclusion