We detail the project achievements by work packages, with WP1, focused on career development and training of the fellow at the end of this section.
# Ecological modelling of coral communities (WP2)
Realistic ecological models allow defining what could happen in a given system under some perturbation or change in environmental conditions, and if a system may undergo a large, abrupt shift or will respond more gradually to perturbations. We built such models based on field experiments and observations, to identify the critical thresholds in perturbations below which a coral community becomes degraded. We show that abrupt transitions may occur in this ecosystem, but their magnitude will depend on the type of neighbor interactions between coral colonies in the field, an aspect of coral ecology only sparsely documented so far. In addition, we show that prior to the abrupt degradation of coral reefs, changes in the spatial structure of reefs are expected. Specifically, we show that coral colonies that are more stressed, and closer to degradation, should also be more ‘clumped’ in space.
These results have been published in The American Naturalist (February 2022), and communicated at conferences (Congreso Ciencias del Mar, Concepción, Chile), as well as in more minor venues, such as workshops and seminars.
# Data collection at Rapa Nui (Easter Island; WP3)
We organized a three-weeks field campaign to Rapa Nui (Easter Island, Chile), to gather the required data to test our hypotheses stemming from the modelling work. This campaign was very successful, despite large delays due to COVID-19 travelling restrictions, and consisted in the 3D mapping of the underwater areas of the island up to a depth of 20m. This was done using "drone-like" surveys with cameras mounted under a small fishing boat. This allowed covering 70% of the island with very detailed (~1 cm resolution) orthophotographies and bathymetry. This is probaly the most complete and broadest dataset documenting the coral communities of this island, an essential baseline for its sustainable management.
# Data analyses and development of indicators (WP4)
Using the novel dataset collected in 2022, we could test our hypotheses regarding the spatial organization of coral cover along stress gradients. We show that the cover of the two dominant coral species becomes more and more clumped as stress increases - here, through increased wave exposure, which reduces the proportion of large clumped, colonies in the seascape, confirming our model predictions. Such change in spatial structure is detectable, while more common metrics of coral system 'health', such as percent coral cover, may not show any change with increasing stress. These results show that an accurate assessment of the fragility of coral ecosystems to perturbations cannot rely only on simple metrics, such as cover, but must include novel indicators, for example based on coral colony morphology or spatial structure. Doing so can be done using the statistical tools we developed along this project.
These results have been communicated at national and international conferences (BES 2023, NAC 2024) and in publications (e.g. Pci Ecology). A high-profile publication is expected in 2024 (manuscript is in edition among co-authors), which will coincide with the public release of the dataset supporting the analyses (see WP3).
# Training, planning and career development (WP1)
This project has been centered around a formative post-doctoral project, involving training, collaboration, student supervision and teaching by the grant fellow. The novel spatial dataset collected in November 2022 has been used for innovative student projects lead by the fellow, both at Master's and undergraduate level. We highlight here the use of the 3D information given by the spatial surveys to estimate the effects of waves on the morphology of corals (First prize for poster at NAC 2024, G. Marroni).
The wide diversity of training, teaching, outreach and and coordination activities of this project, enabled by the excellent assistance and supervision at all involved institutions, has dramatically increased the experience of the fellow, leading to an application to permanent research positions in 2024.
