Role of ecosystem engineers in aquatic habitat restoration

Role of ecosystem engineers (sea lamprey and salmon) in sedimentary processes and aquatic habitat restoration

Coordinators

Anne Julia Rollet and Emilien Lasne

Context and issues

The objective of the dam removal on the Selune River is to restore aquatic ecosystems in the catchment area and aquatic animal and plant populations. One of the conditions for the success of the operation is the reappearance of diversified river forms and diversified aquatic habitats. Ideally, the watercourse would return to its original morphology and dynamics, but the necessary sediment management during the operation has involved human interventions of varying degrees depending on the sector, with likely consequences on the morphology of the watercourse (sinuosity, geometry) and on the nature of the bed substrate (grain size). Sea lampreys and salmon, candidates for recolonization, shape the substrate of rivers by building nests where they lay and cover their eggs. This activity can significantly and durably modify the distribution of sediments in breeding areas and increase the complexity of aquatic habitats.

The reopening of the upstream part of the Selune River to migratory fish provides a unique opportunity to characterize the relationship between fish and geomorphology and to clarify the engineering role of these organisms and their contribution to the renaturation of the Selune River.

Objectives of the project

This project aims to identify and characterize potential breeding habitats in the dewatered areas and their quality with respect to lampreys and salmon, and to characterize the role of these species in morphogenic processes and sediment flows.

 

Methodology

Protocols specific to both river geomorphology (sediment tracing by passive transponders, granulometry, velocity and channel geometry measurements) and fish reproduction monitoring (location and abundance of nests) will be developed at several sites (I) downstream of the dams (comparison of movement frequencies and migration distances of these tracers according to their mobilization or not during spawning), (II) in the former dam impoundment to identify and characterize potential spawning sites, assess the morphological resilience of the channel and then monitor potential spawning areas and their impact on coarse sediment dynamics after erasure.

 

Laboratories involved

Université Rennes 2 (Département de Géographie ) / UMR 6554  LETG

UMR ESE  Agrocampus Ouest-INRA Centre Bretagne-Normandie