PErfECT “Photogrammetry, gEnetics, Ecology for red coral ConservaTion”

 

The PErfECT project is a significant contribution to the conservation of the red coral to ensure its persistence and evolution in the context of global change. Given the structural role of red coral in the coralligenous habitats, the results of PErfECT will benefit to the conservation of the associated biodiversity rich community.

The main results are described in the following sections. These results illustrate in an undeniable way the interest and the strength of the multidisciplinary, integrative and innovative approach developed during the PErfECT project.

 

Objective 1: Identification of conservation objectives for red coral populations

PErfECT sets the conservation goals for the red coral based on the morphological, demographic and genetic characterizations of peculiar colonies (i.e. large sized > 10 cm in height - hundred years old colonies) and well-conserved populations (i.e. non impacted by harvesting) with a high heritage value. Colonies and populations analyzed were sampled within two marine protected areas in the NW Mediterranean: Réserve Naturelle de Scandola (Corsica, France) and Parc Natural del Montgrí, Illes Medes i Cap de Creus. Besides we have the opportunity to characterize large sized colonies from private collections.

For the characterization the large sized red coral colonies, new technological approaches were developed using of digital photogrammetric techniques based on NPR (Non Photo realistic Rendering). In fact, measurements on large colonies characterized by complex shapes and entanglement of the branches pose several constraints. Likewise, the proximity of the substrate on which the colony is fixed may sometimes hamper observations and thus the acquisition of data. The Non-Photorealistic Rendering (NPR) approaches was used to solve these problems. Indeed, these approaches allow, among others, the detection of contours on three-dimensional models, or the hollows or bumps on the structure studied. All this makes it possible to separate the colony from the substrate where it is attached. By skeletization, the model is then reduced to its simplest expression in order to quantify its morphological and dimensional characteristics in an automated way.

A large sized colony of red coral Corallium rubrum from a private collection. Two days of photogrammetric processing on the 800 photos were needed for its analysis. A large sized colony of red coral Corallium rubrum sampled in the field. More than 50 photos were needed for its analysis.
Example of Non-Photorealistic Rendering (NPR) of a large sized red coral colony implemented. Skelezitation process with the colony superposition and resulting skeleton, using the visualizer of (Liu 2010).

 

To define the conservation status of red coral populations, the characterization of size of structure of populations is essential. We developed a tailored and cost-effective photogrammetric tool to measure colony size, to quantify necrosis rates, density and recruitment in red coral populations. A specific module was developed within the Arpenteur software. In this module, we developed of an automatic procedure to orientate and scale a set of photos from the same scenes through the use of coded targets fixed on the quadrat used to monitor the populations. This procedure largely optimizes processing times for the 3D measurements of red coral colonies.

Red coral module developed within Arpenteur to optimize the acquisition of colony sizes. The figure also provide an example on the potos obtained for the photogrammetric analysis.

 

All tools developed within the project are freely available from a devoted section in the website. From this website, the users can download the interface as well as the 3D model file of the quadrats with the coded targets for its 3D printing. This approach guarantee the standardization and the reliability of the demographic monitoring of red coral populations.

Examples of size structure of red coral populations obtained using the photogrammetry approach. Examples of size structure of the effects of warming on red coral populations obtained during the surveys of permanent plots.

 

We characterized the genetic structure and genetic diversity of the same populations surveyed for demographic studies as well as additional populations. Genetic diversity is a crucial parameter in the population responses and adaptation to environmental changes. Moreover, the characterization of population genetic structure allow inferring different evolutionary processes, particularly genetic drift and gene flow, which are central to estimate population recolonization and resilience capacities. These genetic data are thus central for red coral conservation, especially in the context of current warming. In addition, we are thus able to precisely characterize the functioning of populations within the studied marine protected areas. For instance, we are able to identify populations requiring particular conservation attention due to their low genetic diversity or genetic isolation or, on the contrary, because they have a central role as source population in the studied marine protected areas.

Location of the red coral populations from the marine protected area of Scandola (Corse, France) and results of the discriminant analyses of principal components (DAPC). Each circle corresponds to one individual genotyped with microsatellites, while each population is shown with a particular color.

 

To complement the population surveys conducted within PErfECT we reviewed compiled empirical demographic datasets. This meta-dataset was used for the development of novel population modeling studies. The resulting models allowed to explore the demographic trajectories of red coral populations accounting for the impact of the main pressures threating the species: fishing and warming.

The results of this objective have been integrated in a collaborative database CorMedNet developed in the framework of the PErfECT project. The database regroups all the existing data regarding the distribution, demography and genetics of the red coral published to date. This platform is designed for the whole scientific community working on red coral. This database is a reference for the red coral in the Mediterranean Sea which aims to obtain a global estimation of the ecological state of the species. The analysis of the compiled information has been the basis of important outcomes for the conservation of red coral such as the IUCN Mediterranean Atnhozoans red list and the 10 years fishing moratorium of red coral in the Catalan coast.

CorMedNet website.

 

Objective 2: Characterization of the functioning of red coral populations

This objective combined photogrammetric tools with ecology and population genetic to better understand the dynamics of red coral populations. More particularly, we characterized the patterns of spatial genetic structure at fine geographic scale (i.e. between colonies within population) in populations showing contrasted demographic patterns. To reach this objective, we developed a novel photogrammetric tool allowing both the visualization of orthophotos covering a surface of a few square meters and the entry of measurement points directly on the image displayed. The challenge was to provide a simple and effective visualization interface, allowing to have an overall view of the entire monitored area (several m2), while being extremely detailed to identify the colonies. Since the substrate displayed on the orthophoto can show a marked relief, the module has been equipped with an innovative system for calculating the geodetic  distance taking into account the curvatures of the substrate. This module allowed to calculate pairwise geographic distances among hundreds of sampled colonies.

Ortophoto obtained in the Passe Palazzu population. The ortophoto was used to calculate the distances between pairs of hundreds of colonies.

 

We investigated the potential link between population density and reproduction by analyzing 3 populations showing contrasted demographic features (colony size structure and density). A correlation between the genetic relatedness and the geographic distances among individuals was demonstrated in the three populations. These patterns of isolation by distance were directly related to the demographic patterns: the population with highest density also shows the highest correlation. Accordinly, the related demographic processes also vary function of the density: the estimates of effective dispersal were higher in the low density population. In complement, a trend toward a simplification of the network of sibships among colonies function of the density was revealed in these populations. These results demonstrate for the first time the complexity of the interaction between demographic and evolutionary processes in the red coral. They suggest that distinct breeding units, which sizes vary function of the population demography, compose red coral populations. These results have direct implications to optimize restoration efforts needed in red coral populations showing clear signs of decline due to fishing, poaching or climate driven mortalities.

Module developed during PErfECT to calculate distances among colonies and the resulting map showing the positions of colonies. The graph shows a significant relationship between genetic distance and the distance suggesting that genetically related are closer in space. Adults and juveniles are shown dots.

 

For more details in the results check the published papers.