Biomass Mapping for an Improved Understanding of the Contribution of Cold-Water Coral Carbonate Mounds to C and N Cycling

Laurence Helene De Clippele,Evert De Froe,Sandra Rosa Maier,J Murray Roberts,Anna-Selma Van Der Kaaden

doi:10.3389/fmars.2021.721062

Laurence Helene De Clippele, Evert De Froe + Show 3 more

Open Access

https://doi.org/10.3389/fmars.2021.721062

Copy DOI

Abstract

This study used a novel approach combining biological, environmental, and ecosystem function data of the Logachev cold-water coral carbonate mound province to predictively map coral framework (bio)mass. A more accurate representation and quantification of cold-water coral reef ecosystem functions such as Carbon and Nitrogen stock and turnover were given by accounting for the spatial heterogeneity. Our results indicate that 45% is covered by dead and only 3% by live coral framework. The remaining 51%, is covered by fine sediments. It is estimated that 75,034–93,534 tons (T) of live coral framework is present in the area, of which ∼10% (7,747–9,316 T) consists of Cinorg and ∼1% (411–1,061 T) of Corg. A much larger amount of 3,485,828–4,357,435 T (60:1 dead:live ratio) dead coral framework contained ∼11% (418,299–522,892 T) Cinorg and &lt;1% (0–16 T) Corg. The nutrient turnover by dead coral framework is the largest, contributing 45–51% (2,596–3,626 T) C year–1 and 30–62% (290–1,989 T) N year–1 to the total turnover in the area. Live coral framework turns over 1,656–2,828 T C year–1 and 53–286 T N year–1. Sediments contribute between 1,216–1,512 T C year–1 and 629–919 T N year–1 to the area’s benthic organic matter mineralization. However, this amount is likely higher as sediments baffled by coral framework might play a much more critical role in reefs CN cycling than previously assumed. Our calculations showed that the area overturns 1–3.4 times the C compared to a soft-sediment area at a similar depth. With only 5–9% of the primary productivity reaching the corals via natural deposition, this study indicated that the supply of food largely depends on local hydrodynamical food supply mechanisms and the reefs ability to retain and recycle nutrients. Climate-induced changes in primary production, local hydrodynamical food supply and the dissolution of particle-baffling coral framework could have severe implications for the survival and functioning of cold-water coral reefs.

Highlights

Cold-water coral (CWC) carbonate mounds are important marine ecosystems (Roberts et al, 2009)
Biomass maps can guide sampling and monitoring expeditions and our current approach can be applied to other habitats, to provide large-scale maps of biomass, hotspots of metabolic activity and nutrient mineralization, in particular in the understudied, but large deep-sea realm
The predictive power of this approach can be improved by adding more coral surface area data, especially where the coefficient of variation of the map is higher

Summary

Introduction

Cold-water coral (CWC) carbonate mounds are important marine ecosystems (Roberts et al, 2009) They are topographic seafloor structures that can be several hundreds of meters in height and have accumulated through successive periods of reef development, sedimentation and (bio)erosion over glacialinterglacial periods (Kenyon et al, 2003; Van Weering et al, 2003; Mienis et al, 2007; Roberts et al, 2009). Baffling of currents caused by the coral framework can locally increase the POM concentration at the reefs (Soetaert et al, 2016)

Methods

Results

Discussion

Conclusion