| 28 Jul 2025
A first predictive mechanistic model of cold-water coral biomass and respiration based on physiology, hydrodynamics, and organic matter transport
Abstract. Cold-water corals form complex three-dimensional structures on the seafloor, providing habitat for numerous species and act as a carbon cycling hotspot in the deep-sea. The distribution of those important ecosystems is often predicted by statistical habitat suitability models, using variables such as terrain characteristics, temperature, salinity, and surface productivity. While useful, these models do not provide a mechanistic understanding of the processes that facilitate cold-water coral occurrence, and how this may change in the future. Here, we present the results of a mechanistic process-based model in which coral biomass and respiration are predicted from a 3D coupled transport-reaction-model for south-east Rockall Bank (NE Atlantic Ocean). Hydrodynamic forcing is provided by a high-resolution Regional Ocean Modelling System (ROMS) model, which drives the transport of reactive suspended particulate organic matter in the region. The physiological cold-water coral model, with coral food uptake, assimilation, and respiration as key variables and with model parameters estimated from available experimental report, is coupled to the reactive transport model of suspended particulate organic matter. Model predictions agree with coral reef biomass and respiration observations in the study area and coral occurrences comply with predictions from previously published habitat suitability models. Cold-water coral biomass was mainly predicted on coral mounds and ridges in the area. Filter feeding activity by cold-water corals proved to strongly deplete food particles in the bottom waters. Replenishment of food particles by tidal currents was therefore vital for cold-water coral growth. This mechanistic modelling approach has the advantage over statistical and machine learning-based predictions that it can be used to obtain an understanding of the effect of changing environmental conditions such as ocean temperature, surface production export, or ocean currents on cold-water coral biomass distribution and can be applied to other study areas and/or species.
OS manuscript egusphere-2025-3385
Reviewer Comments
General comments
Scientific significance
De Froe and co-workers use a predictive mechanistic model to estimate cold- water coral biomass distribution and respiration. Their model successfully reproduces observed reef biomass and respiration patterns. The advantage of this approach can be used to obtain the effect of changing environmental conditions such as ocean temperature, export production or ocean currents.
The study presents a first mechanistic model predicting cold-water coral biomass distribution based on organic matter transport and hydrodynamics. The authors set up the model by cleverly coupling three models, offering a new perspective on the mechanisms driving coral distribution. They demonstrate that coupling organic mater uptake with the cold-water coral model is key to predicting the spatial distribution of these corals.
The authors clearly identify existing gaps in the field and present a study that brings new knowledge and tools that can be applied in future research.
Scientific quality: yes, excellent.
Presentation quality: The manuscript is clearly written and well-structured. The number of figures, conceptual diagrams, and tables is appropriate, and they are of high quality. The supplemental material is warranted and adds value. The authors also discuss the limitations of their work, and the conclusions are well-supported and justified.
I am very positive towards the study, as the findings are important.
Specific comments and detail points:
Line 87 : “This feedback between organisms and their environment can greatly affect how they respond to environmental changes: by modifying their own environment, organisms can rearrange their spatial patterns in response to climate change thereby avoiding a tipping point towards extinction (Rietkerk et al., 2021)” could be reworded. The temporal aspects are not fully resolved within the time scale of the study. Also add a reference relevant to corals.
References in introduction and discussion : Consider reducing to 3-4, as some currently contain five. This will improve readability and focus.
Line 163: replace “ numerous associated animals” with “numerous associated organisms”.
Lines 508-510: The authors could be more specific in this section to enhance clarity and strengthen the argument.
Lines 581 to 585: This section needs to be better explained, particularly the last sentence. I recommend splitting it into two sentences for improved clarity and flow.
References : There are some inconsistencies in formatting within the reference list. Please revise to ensure uniform style throughout.