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The role of ecosystem engineer species (sea lamprey) in sedimentary processes and the restoration of aquatic habitats

Coordinator(s)

Anne-Julia Rollet and Emilien Lasne

Scientific context

The aim of removing the dams on the Selune is to restore ecological continuity and aquatic and riparian ecosystems in the catchment area. One of the conditions for the success of the operation is the reappearance of river forms and diversified aquatic habitats. Ideally, the watercourse would return to its original course and dynamics, but the need to manage sediments has involved human intervention of varying degrees depending on the sector, with probable consequences for the morphology of the watercourse (sinuosity, geometry) and the nature of the bed substrate (granulometry).

The sea lamprey, a candidate for recolonisation, shapes the substrate of watercourses by building nests where it lays and covers its eggs. This activity can significantly and sustainably modify the distribution of sediments in breeding areas and increase the complexity of aquatic habitats. The reopening of the upstream section of the Selune to migratory fish provides a unique opportunity to characterise the fish-geomorphology relationship, and to clarify the role of these species as an ecosystem engineer and their contribution to the restauration of the Selune.

Subject(s) of study

The project focuses on a migratory species that plays an important role in sedimentary processes and river morphology: the sea lamprey.

Objectives

The project aims at:

1. Identifying and characterising potential breeding habitats in the restaured sections and their quality for sea lampreys.
2. Characterise the role of this species in morphogenic processes and sediment flows.

Methods

Protocols specific to fluvial geomorphology (sediment tracing using passive transponders, granulometry, measurements of speeds and channel geometry) and to monitoring fish reproduction (location and abundance of nests) will be implemented at several sites:

• Downstream of the dams, by comparing the frequencies of movement and migration distances of sediment tracers according to whether or not they are mobilised during spawning,
• In the former reservoir of the dams in order to identify and characterise potential spawning sites, assess the morphological resilience of the channel and then monitor potential spawning areas and their impact on coarse sediment dynamics after the dams have been removed.

Laboratories involved

• Department of Geography and Spatial Planning, UFR Social Sciences, Université Rennes 2
• LETG - UMR Coastline Environment Remote sensing Geomatics, Rennes
• DECOD - UMR Ecosystem Dynamics and Sustainability: from source to ocean, INRAE/Institut Agro/Ifremer, Rennes