Farming-up coastal fish assemblages through a massive aquaculture escape event

• An aquaculture massive escape released 1.5 million fish into the wild in the Canaries.
• Mean trophic level of marine fish assemblages was investigated through visual census.
• Diet of escaped sea bass was studied regarding size and time in the wild.
• Mean trophic level was raised but a nearby marine protected area showed resilience.
• Escaped sea bass exploited natural resources according to size and time at liberty.

We investigated the changes on the mean trophic level of fish assemblages across different spatiotemporal scales, before and after a massive escape event occurred off La Palma (Canary Islands), which resulted in the release of 1.5 million fish (mostly Dicentrarchus labrax) into the wild. The presence of escaped fish altered significantly the mean trophic level of fish assemblages in shallow coastal waters. This alteration was exacerbated by the massive escape. A nearby marine protected area buffered the changes in mean trophic level but exhibited the same temporal patterns as highly fished areas. Moreover, escaped fish exploited natural resources according to their total length and possibly, time since escapement. New concerns arise as a “farming up” process is detected in shallow coastal fish assemblages where marine aquaculture is established.