Developing and testing spatial indicators of ecosystem stability for subtidal seascapes

Informations projet

INDECOSTAB

N° de convention de subvention: 896159

DOI

10.3030/896159

Projet clôturé

Date de signature de la CE 17 Avril 2020

Date de début 22 Mars 2021

Date de fin 21 Mars 2024

Financé au titre de

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Coût total

€ 205 969,92

Contribution de l’UE

€ 205 969,92

Coordonné par

UNIVERSITEIT UTRECHT
Netherlands

Periodic Reporting for period 2 - INDECOSTAB (Developing and testing spatial indicators of ecosystem stability for subtidal seascapes)

Période du rapport: 2023-03-22 au 2024-03-21

Résumé du contexte et des objectifs généraux du projet

Coral reefs are being threatened worldwide due to ocean warming, acidification, or other sources of local stress such as pollution. This has triggered in many areas the degradation of reefs into algae-dominated seascapes, where coral cover and biodiversity is often much lower, and unable to support essential ecosystem services. This has prompted researchers to find new approaches to identify coral communities that are endangered and at risk of such degradation. This projects uses mathematical models and detailed spatial data to help identifying which coral communities are at risk of degradation, and which ones may be more resilient in the short term.

We use the coral communities of Rapa Nui (Easter Island) as model system. This isolated island in the south-pacific constitutes the limit of tropical corals, which are mainly threatened by ocean warming, and associated heatwaves that can trigger large-scale mortality events. Our models and novel large-scale spatial surveys of coral communities help identify under which environmental conditions coral communities are able to persist, and which critical levels in disturbance are not to be exceeded. This effort goes along with a growing effort on the island to better understand, manage and protect these vibrant coral communities that are essential for fishing, touristic activities (such as recreational diving) and support species of commercial interest.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

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.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

This project advances both our theoretical understanding of coral communities and the approaches we can use to improve their conservation in the current context of global changes, both at Easter Island and elsewhere in the world. The use of novel, large-scale sampling methods based on “drone-like” mapping of underwater reefs has provided for the first time the most detailed surveys of the coral communities of the island, along with detailed bathymetry. Both the scientific findings, along with the gathered datasets will or have been made available to the scientific community and the general public, and distilled through social media and outreach activities. This project is part of an ever-growing effort to conserve coral reefs worldwide, and develop efficient management and conservation strategies for the remote and isolated ecosystem of Easter Island. This is necessary for the sustainability of essential economic activities on the island, including tourism and fishing.

The central message emerging from our results is that the monitoring of coral systems health through time cannot only rely on traditional metrics, such as the percentage of coral cover in standardized quadrats, but must include novel metrics, such as the ones we propose, based on spatial structure, or on coral colony morphologies. Such novel monitoring variables can be tested and implemented on empirical datasets with the tools we developed and provide with this project, and will lead to a better forecast of the response of coral ecosystems, both at Rapa Nui and in other ecoregions of the world.

3D reconstruction of the seafloor, showing a almost-complete coverage of coral colonies

Boat transects used to produce 3D maps of seascapes of very high resolution (inset).

Boat surveys (red tracks) covered approximately 70% of the island shallow subtidal coral communities