Hennige, S. | Search bioRxiv

bioRxiv2024

Regional Variations in Live Proportions of Southwest Pacific Cold-Water Coral Solenosmilia variabilis Reefs

Reef-building cold-water-corals (CWC) form deep-sea habitats that can create biodiversity hotspots. As live coral and dead intact framework provide disparate ecosystem services and are vulnerable to different anthropogenic stressors, it is important to quantify the proportions of each on CWC reefs. We analysed 1,160 images of Solenosmilia variabilis reefs at four sites off New Zealand (Valerie and Forde Guyots at the Louisville Seamount Chain & Ghoul and Gothic Seamounts at the Graveyard Seamount Complex) to determine the ratio of live coral to the whole reef area (termed live:reef). We found live:reef ratios are significantly different between sites at the offshore Louisville Seamount Chain and onshore Graveyard Seamount Complex. This could be driven by reef position relative to the aragonite saturation horizon (ASH) as corals in the Louisville Seamount Chain live below the ASH in colder and deeper waters than those at the Graveyard Seamount Complex, which live above the ASH. In the southwest Pacific, depth is a driver of live:reef ratios, with a larger proportion of live coral at shallow depths and dead intact framework at deeper depths. The live:reef ratios at Gothic Seamount within the Graveyard Seamount Complex remained stable between 2015 and 2020 despite significant differences in live coral, dead intact framework, and reef structure surface area. Our results indicate live:reef ratios can be used to estimate the amount of dead intact framework threatened by shoaling ASH due to ocean acidification at each site, which can help inform which sites could be protected as possible climate change refugia.

ecology↗

bioRxiv2022

Towards modelling cold-water coral reef-scale crumbling: Including morphological variability in mechanical surrogate models

The structural complexity of cold-water corals is threatened by ocean acidification. Increased porosity and weakening of structurally critical parts of the reef framework may lead to rapid physical collapse on an ecosystem scale, reducing their potential for biodiversity support. We can use computational models to describe the mechanisms leading to reef-crumbling. How-ever, the implementation of such models into an efficient predictive tool that allows us to determine risk and timescales of reef collapse is missing. Here, we identified possible surrogate models to represent the branching architecture of the cold-water coral species Lophelia pertusa. For length scales greater than 13 cm, a continuum finite element mechanical approach can be used to analyse mechanical competence whereas at smaller length scales, mechanical surrogate models need to explicitly account for the statistical differences in the structure. We showed large morphological variations between L. pertusa colonies and branches, as well as dead and live skeletal structures, which need to be considered for the development of rapid monitoring tools for predicting risk of cold-water coral reefs crumbling. This will allow us to investigate timescales of changes, including the impact of exposure times to acidified waters on reef-crumbling.

bioengineering↗