Trawl fishing disturbance and medium-term macroinfaunal recolonization dynamics: A functional approach to the comparison between sand and mud habitats in the Adriatic Sea (Northern Mediterranean Sea)

Demersal fishing gear affects seabed habitats both directly and indirectly and modifies the processes and dynamics of benthic communities. At present, scientific attention is focused on using the functional approach to better understand the constraints that drive the recolonization of benthic fauna subjected to fishing disturbance. The Northern Adriatic Sea has an extensive trawlable area that is intensively exploited by a variety of trawling gear. Among these, the rapido, a beam trawl used to catch flatfishes on mud substrate and pectinids on sand, appears to have the greatest impact on the benthic habitat. We used various functional indicators (diversity indices, community structure, trophic groups, production analysis, and exergy) to compare the medium-term (9-months) macroinfaunal recolonization processes in sand and mud habitats treated with a single experimental rapido haul. Recolonization was found to be a community-wide process. The early successional stages in the sand habitat were dominated by scavenging organisms that peaked in abundance 7 d after the treatment. In the mud habitat, the trend in scavenger activity was less distinct, although a peak in abundance was recorded I month after the treatment. The functional analyses revealed that complete recovery required at least 9 months in both habitats. Finally, data collected on the fishing ground near the sand experimental area were analyzed in order to investigate the chronic disturbance caused by commercial trawling. The fishing ground samples showed a higher spatial heterogeneity than the sand experimental samples. Total abundance, total biomass, and production values in the fishing ground were comparable with the lowest recorded values in the sand experimental area, and the exergy differences suggested that the fishing ground's benthic community remained in an early successional stage.