Pacific coral reef growth: Past and present

Dr Emma Ryan

School of Environment

Background

Emma is a coral reef and coastal geomorphologist, interested in how Pacific coral reefs and coastlines change over a range of spatial and temporal scales. Coral reefs provide a natural protective barrier for coastal communities, as reefs dissipate incoming offshore wave energy, limiting the wave energy that reaches island shorelines. Pacific coral reefs and associated landforms are at the forefront of global discussions around climate change, with some studies suggesting that coral reefs may cease growing due to climate change impacts, such as increasing sea surface temperatures and ocean acidification. A reduction or cessation in coral reef growth would be devastating for Pacific communities. However, we know very little about past and present growth rates of Pacific coral reefs and without a baseline understanding of coral reef growth rates, monitoring and projecting future changes is challenging. Under a Faculty of Science-funded project, Emma is starting to tackle this issue by establishing and testing new methodologies for measuring reef growth on Pacific reef flats.

The project

This two-year project, ending in December 2024, will provide the first in situ measurements of reef growth rates in the Pacific. Reef growth rates are being measured using close range structure-from-motion photogrammetry on a reef flat in Nuku’alofa, the Kingdom of Tonga. Emma completed one round of field work in July 2023, where baseline sites were established on the outer reef flat and initial surveys were undertaken. During a field campaign in July 2024, Emma will work together with Tongan government agencies in re-surveying the sites to establish the amount of reef growth/erosion in the one-year time period. Validation of the method accuracy and precision is being undertaken through laboratory ‘reef’ comparisons and on a rock platform in NZ, in conjunction with laser scanning. This pilot project will provide the foundation for future grant applications to continue monitoring reef accretion in Tonga, and hopefully across many other locations in the Pacific. A Pacific-wide reef accretion monitoring network would be hugely valuable in improving our understanding of reef response to climate change, and associated impacts of increasing sea-level rise on coastal communities and infrastructure.