Marine Lechene is from New-Caledonia and studied in France and Australia. She completed her Bachelor's in Biology and Ecology from The University of Montpellier (France) and Master's in Marine Science and Management from The University of Sydney (Australia).

Spatio-temporal variation in the size, distribution, growth and mortality of dominant hard coral taxa on the GBR

2021 to 2025

Project Description

Sustained and widespread degradation of coral reef ecosystems, manifested largely as declines in the abundance of scleractinian corals, is threatening the structure and function of these important and diverse ecosystems. While coral loss and reef degradation have been well documented, the role of demographic rates and spatial distributions of corals in structuring coral reef populations and communities are yet to be fully understood. This project will investigate the role of coral colony survival and spacing in the viability of coral populations for a range of representative coral taxa across habitats. During this project, communication tools will be developed (e.g., 3D models in virtual reality) to connect with researchers, traditional owners and students.

Project Importance

Demographic rates and spatial distribution of individually tagged colonies in a population has only ever been done for a few coral species with small sample sizes and across restricted spatial scales. Colony planar area better captures the overall shape and size of corals than conventional methods (e.g., maximum diameter), but has rarely been measured in situ and the lack of standardised method to measure colony size and changes in dimensions has been widely recognised (Pratchett et al., 2015). This hampers our understanding of the role of demographic rates and spatial distribution of coral colonies in structuring coral populations and represents a critical research gap. This project will investigate the role of spatiotemporal variation in coral distribution, growth and mortality in structuring coral populations for a range of representative coral taxa across habitats. The proposed methods will result in precise quantification of coral size with planar area empirical measures rather than approximations and relate changes in size to differences in colony location, spacing and habitat 3D characteristics. This project will contribute to contemporary landscape, population and resilience ecological theories as well as their applications to better understand and manage this difficult-to-access and under-measured biome.

Project Methods

Imagery was collected following photogrammetric procedure as part of the Ecological intelligence for reef restoration (EcoRRAP) sub-program (https://gbrrestoration.org/program/ecorrap/). We selected three offshore (Davies, Little Broadhurst and Chicken) and two inshore (Pelorus and Orpheus) reefs for this study. Within each reef, permanent sites on the reef slope were chosen to encompass different habitats (front, back, flank and lagoon) and depths (shallow 3-8m and deep 10-15m – where possible). Each year and at each of the reef sites, we conducted four replicate surveys (plots) of approximately 12 x 6m. A total of 2000-6000 images were taken at each plot for each year. Images were then imported into Agisoft for 3D processing using custom python scripts to build 3D models and 2D orthomosaics of each plot. Coral size were then extracted for 6 morphotaxa (Acropora tabulate, Porites massive, A. millepora, S. pistillata, P. verrucosa, P. damicornis) using both 2D orthomosaics (planar area) and 3D models (surface area and volume) to calculate coral growth across 2 years (2021-2023). Colonies that bleached during the early 2022 bleaching event were also recorded. This project examined or will examine: (1) the accuracy of co-registration of 3D models using a sphere-based process; (2) the spatio-temporal variation in the size structure of 6 dominant morphotaxa across habitats; (2) the spatial variation in the 3D growth of those same taxa and (3) the effect of bleaching and environmental variables on growth.

Project Results

This project will improve forecasting the ability of future coral reef to cope with environmental change based on information on rates of recovery and adaptation of coral reef taxa (AIMS Science Outcome #6). It will thus enhance management of tropical coral reef ecosystems by informing on where and at what scale coral reef restoration interventions are needed (AIMS Science Outcome #4). This project uses innovative, efficient and cost-effective photogrammetry methods (AIMS Science Outcome #2) to collect data at large spatial and temporal scales relevant to the study scope. At the end of the project, we will better understand the spatial and temporal variation of demographic rates of dominant morphotaxa which are key indicators of reef health; how these demographic rates change after an acute disturbance and how this response varies depending on reef complexity and environments.

Keywords

Benthic,
Biostatistics,
Climate change,
Coral reefs,
Corals,
Crown of Thorn Starfish,
Distribution,
Ecology,
Field based,
Interaction,
Management tools,
Mapping,
Marine planning,
Modelling,
Monitoring,
Ocean acidification,
Ocean warming,
Physiology,
Quantitative marine science,
Remote Sensing,
Taxonomy,
Temporal change