Capacity for recovery of rocky subtidal assemblages following pollution abatement in a scenario of global change

- We examine the effectiveness of a sewerage scheme in terms of subtidal algae recovery.
- Disturbed vegetation showed evidences of partial recovery.
- Canopy-forming macrophytes showed no signs of recovery 11 years after the clean-up was completed.
- Resilience of the ecosystem may be reduced after long-standing disturbance.
- Climate variability could be affecting the recovery trajectory of disturbed assemblages.

The successful protection and management of marine ecosystems depend on understanding the capability of biota for recovering after stressor mitigation actions are taken. Here we present long-term changes (1984-2012) in degraded subtidal assemblages following the implementation of the sewerage scheme for the metropolitan area of Bilbao (1 million inhabitants). Qualitative and quantitative species composition of disturbed vegetation shifted over time, making it more similar to that of the reference assemblages considered. Species density in the disturbed habitats increased, which is also a positive sign of recovery. However, eleven years after the clean-up was completed, canopy-forming macrophytes showed no signs of recovery. We argue that the ecological resilience of the ecosystem may have been eroded after a long-standing pollution perturbation and that underlying climate change could be influencing the recovery trajectory of the degraded assemblages. The implications of these conclusions for the implementation of European marine environmental legislation are discussed.