Coral symbiont (nitrogen & chlorophyll) & coral host nitrogen (GBR4 BGC v3.1 baseline)

What do these visualisations show?

These visualisations show model results of the uptake of nitrogen by corals, showing how much is contained in the coral tissue (coral host nitrogen) and how much is contained in the symbiotic zooxanthellae algae that grow inside the coral (coral symbiont).

These maps show that the coral nutrient and chlorophyll levels change very slowly over time. The main effect that can been seen in these visualisations is that the corals increase their chlorophyll density (and its corresponding nitrogen levels) during the winter months when the light levels are lower.

Limitations

These visualisations show some of the internal dynamics of the coral modelling performed in the BGC. This model uses a 'single polyp' model that estimates the nutrient dynamics created by the coral in each grid cell of the model. This coral model helps the BGC to capture the nutrient dynamics caused by the uptake and release of nitrogen of corals as they grow and the effect they have on the PH of the water as they calcify their skeletons.

The BGC coral model and these matching visualisations should only be used as a guide for better understanding the BGC model and not as a reflection of the state of coral on the GBR. The BGC model does not include a detailed coral ecosystem model and thus does not provide an estimate of coral cover. It does not consider the effects of coral mortality caused by cyclones, disease or Crown-of-Thorns Starfish and so only provides a first approximation to how the coral reefs affect water chemistry.

This coral model is limited to coral reef areas (as determined by the GBRMPA reef features dataset), which is why there are only non-zero values over coral reef pixels. Additionally the model does not consider coral reefs in Torres Strait as these reefs were not included in the GBRMPA reef features dataset used to configure the model.

Note: The visualisations for the monthly and yearly aggregations are based on regridded data (converting the original raw model data from a curvilinear grid to a regular rectangular grid). This process uses interpolation to perform the regridding process. Since this data is very discontinuous (zero everywhere, except for coral reef pixels) this interpolation results in visual anomalies around the boundaries of the reefs as the interpolation smooths the transition from the coral reef pixels to zero for open water.

Coral symbiont N

Concentration of nitrogen biomass per m² of coral symbiont cells, or zooxanthellae. C:N:P is 106:16:1. Light is accessed in the following order: Macroalgae, Seagrass, Coral.

Coral symbiont Chl

Concentration of chlorophyll biomass per m² of coral symbiont cells. As chlorophyll is the only pigment resolved in the coral symbiont, ci represents the sum of the concentration of all photosynthetic pigments within the cell and has an absorption spectrum of divinyl chlorophyll a. Light is accessed in the following order: Macroalgae, Seagrass, Coral.

Coral host N

Concentration of nitrogen biomass per m² of coral host tissue in the entire grid cell. Unlike other epibenthic variables, corals area is assumed to exist in communities that are potentially smaller than the grid size. The fraction of the grid cell covered by corals is given by A_CH. Thus the biomass in the occupied region is given by CH/A_CH. The percent coverage of the coral of the bottom for the whole cell is given by A_CH (1 - exp(-Ω_CH CH/A_CH)). With only one type of coral resolved, CH represents the biomass of all symbiotic corals. Since the model contains no other benthic filter-feeders, CH best represent the sum of the biomass of all symbiotic filter-feeding organisms such as corals, sponges, clams etc. C:N:P is 106:16:1. Light is accessed in the following order: Macroalgae, Seagrass, Coral.