Improving estimates of coral reef carbonate budgets using habitat-specific rates

The growth and persistence of coral reefs is dependent on the positive balance between calcium carbonate (CaCO₃) production and erosion—often referred to as a ‘carbonate budget’. Carbonate budgets are increasingly being used as a key metric to establish reef condition.

In our recently published study, we quantified the biogenic carbonate production, erosion and dissolution within and between five distinct habitats of Heron Reef on the southern Great Barrier Reef.

Our study has improved on past estimates by:

1. Investigating multiple habitats discretely; and
2. Directly quantifying habitat-specific growth, erosion and dissolution of individual organisms.

We found that framework carbonate production and bioerosion varied significantly between habitats at Heron Reef, with net carbonate budgets generally lower within the lagoon compared to reef slope sites.

On the exposed reef slope, the net framework carbonate budget was significantly lower due to localised damage from Tropical Cyclone Hamish, which occurred seven years prior to the study.

Although the reef slope habitat is proportionally only 13 percent of the reef platform, it contributes about 50 percent to reef-scale carbonate production—more than any other geomorphological habitat on Heron Reef.

The reef-scale carbonate budget was determined by considering site-specific budgets and area of each habitat. This was estimated at 4.06 kgCaCO₃ m^-2 yr^-1.

The comprehensive carbonate budget presented here can be used as a ‘baseline’ for future studies in the context of climate change. Though, it is improbable that reefs like Heron Reef will be able to maintain coral cover and carbonate production at current levels due to predicted increases in storm intensity, intensifying ocean warming, and acidification on near-future reefs.

Our results emphasise net carbonate budgets exhibit significant spatial variation within and between geomorphological habitats across a single platform reef system. And our assessment of Heron Reef reinforces the importance in using current, site-specific data to calculate biogenic net carbonate production, erosion, and dissolution.

Future studies should consider habitat-specific sediment import and export as well as mechanical erosion to comprehensively understand if future growth rates will be able to track changes associated with the world’s current rate of CO₂ emissions.

PAPER

Brown K, Bender-Champ D, Achlatis M, van der Zande R, Kubicek A, Martin S, Castro-Sanguino C, Dove S, Hoegh-Guldberg O. (2020). ‘Habitat-specific biogenic production and erosion influences net framework and sediment coral reef carbonate budgets’. Limnology and Oceanography. DOI: 10.1002/lno.11609