Evaluation and Development of indicators to characterise and assess coastal and ultra-coastal marine ecosystems: application to climate change and ecological monitoring.


Fisheries acoustics is now widely used for stock assessment (Brehmer et al., 2006; Doray et al., 2010). However, the indicators used do not always make it possible to respond to other problems, such as the functioning of ecosystems, their monitoring or their links with changes in the environment. Our study aims to develop effective indicators to assess and monitor the state of health of various coastal and ultra-coastal ecosystems. Our work will be articulated in three components: the implementation of descriptors; validation of their effectiveness with the PREFACE project dataset (Enhancing Prediction of Tropical Atlantic Climate and its Impacts; European Commission FP7); their application in the ACaPELA project (Method for hydroacoustic monitoring of coastal fish and cephalopods within the framework of the DCSMM, FEAMP project).

The first part of the doctoral work will focus on the establishment and validation of effective descriptors for the assessment, understanding and monitoring of ecosystems. These descriptors will help to grasp the links between ecosystems and their environment, and in particular the impacts of climate change, overfishing and various other anthropogenic pressures. The implementation of these descriptors will be supported by the Tropical Atlantic Ocean dataset which offers a unique dataset for the Tropical Atlantic Ocean, on 3 contrasting ecosystems and over several years. The descriptors will be particularly focused on small pelagics as well as SSLs (Sound Scattering Layer) (Béhagle, 2015; Diogoul et al., 2020, 2019).

The second part of the thesis will validate the choice of these descriptors by applying them to the dataset of the tropical Atlantic Ocean in order to improve the understanding of the different ecosystems studied. These data focus on the tropical Atlantic, which has experienced persistent climate change over the past century, as well as pronounced multi-decade changes (Demarcq et al., 2018). The African countries bordering the Atlantic are highly dependent on their ocean for the development of society, fishing and tourism (Lancker et al., 2019). They have been strongly affected by these climate changes and will have to face major adaptations associated with future global changes. The three LMEs (Large Marine Ecosystem) of West Africa are taken into account: the Canary Current LME, the Benguela Current LME and the Guinea Current LME with data recorded over 15 years. The descriptors will be effective in discriminating the different ecosystems, comparing and studying their respective functioning and allowing monitoring over time in connection with physical, environmental data and anthropogenic pressure gradients.

The last part will apply the descriptors previously validated to the ACaPELA project which, within the framework of the DCSMM (Marine Strategy Framework Directive), "aims to achieve and / or maintain the good ecological status of the different marine ecosystems". The objective of this project is to complement current fishing campaigns with a protocol and equipment adapted to work at shallow depths. The acoustic material consists of an EK80 (Simrad, 2018) and a high-frequency multibeam sonar (Mezotech Simrad M3, 500 kHz) (Kongsberg, 2019). Acoustic data are supplemented by data from fishing, diving and optical systems. This work requires the development of a data acquisition protocol and an ad hoc methodology for their processing. The routine use of these methodologies will make it possible to complete the already existing fishing campaigns on more important areas of the plateau and the descriptors will allow a more global analysis and monitoring of the state of the ecosystems according to environmental and pressure gradients in order to meet the objectives of the MSFD.

More specifically, our work also aims to establish descriptors to optimize the use of acoustic data in order to assess and monitor the state of coastal and ultra-coastal ecosystems in two different systems: the continental slope in West Africa and the ultra-coastal fringe in North Brittany.