European Ocean Biodiversity Information System

Introduction: The reopening of tidal channels beneath the new bridges over the La Rabia and El Capitán estuary arms was expected to generate significant hydrodynamic, morphological, and ecological changes in the Oyambre estuary. The recovery of the estuary’s physical structure and functionality largely determines its ecological evolution. Therefore, ecological monitoring, conducted in parallel with the assessment of physical changes, is essential to evaluate the restoration process and to develop operational protocols that optimize future restoration outcomes. The restoration of the Oyambre estuary affects multiple components of the estuarine ecosystem that are closely interrelated and strongly dependent on habitat characteristics. Ecological restoration, therefore, seeks a holistic recovery of both structural and functional aspects of the system. Evaluating this recovery requires a long-term, systematic study of benthic fauna, as well as the relationship between biological variations and changes in physical habitat properties (hydrodynamics, water and sediment quality, morphology, etc.). Monitoring programs of this kind provide essential information for designing effective restoration projects. They form the basis of adaptive management, enabling the identification of specific interventions needed to achieve ecological objectives and to guide evidence-based decision-making.

Getting Started: The evolution of benthic macroinvertebrate communities was assessed through sampling at eight stations distributed along three transects within La Rabia estuary arm and one transect within El Capitán estuary arm. These transects were selected to capture different environmental gradients resulting from the restoration of tidal flow (e.g.: upstream penetration of saline water and the downstream movement of fluvial water; changes in tidal range and inundation frequency behind the bridge). At each transect, two sampling stations were established at different intertidal levels (upper and lower). Each station was sampled using a 1,250 cm² corer. All organisms were identified to the lowest possible taxonomic level, counted, and weighed. The temporal resolution varies along the years. 

Purpose: The main purpose of this study is to monitor the natural ecological evolution of the Oyambre estuary (La Rabia and El Capitán estuary arms) following the modification of the a road bridge. The monitoring program aims to evaluate the progress of estuarine restoration after the reestablishment of tidal flow and to assess the ecological response of the system. The results will support adaptive management and provide guidance for future restoration projects, ensuring that ecological, hydrodynamic, and morphological objectives are achieved efficiently.