As part of the ARCO project (TED2021-129426B-I00), funded by the Spanish Ministry of Science, Innovation, and Universities, sediment cores were collected on the trawled Palamós (also known as La Fonera) submarine canyon (NW Mediterranean) in four sampling areas: two sites at a depth of ~500 m (one site trawled and the other untrawled), one site at 800 m, and one site at 2000 m. This sampling design replicates that used approximately 10 years ago, which revealed a depletion of the sedimentary organic load and a slowing of remineralization processes along fishing grounds due to chronic bottom trawling.

The sediments were analysed for biochemical composition (proteins, carbohydrates, lipids, and phytopigments) and extracellular enzymatic activities. The results were compared with those obtained a decade earlier by estimating the magnitude of trawling effects using an effect size metric.

The findings show that, unlike that from 10 years ago, the organic load in trawled sediments does not differ from that in untrawled sediments at the same depth and is higher than that observed at greater depths. Analysis of effect size across the two study periods indicates a significant reversal of the trawling consequences on organic loads, which now appears quantitatively reduced compared to a decade ago.

Conversely, carbon degradation rates in trawled sediments remain lower than those in untrawled sediments, regardless of depth. Given that between the two study periods (in late-2017) the trawling gear from the Palamós fishermen guild was modified, changing from demersal to pelagic trawl door models to prevent them from contacting the seabed, these results suggest that while organic carbon accumulation in the sediments shows some resilience, the functioning of the benthic system remains significantly altered. This indicates that, at least at 500 m depth, the effects of chronic trawling persist in the long term despite mitigation efforts.