Impact of recreational harvesting on assemblages in artificial rocky habitats

Man-made structures have become ubiquitous features of coastal landscapes. These artificial habitats are popular recreation sites. Patterns and effects of recreational activities were investigated from 1999 to 2004 on coastal structures along 40 km of shoreline in the Emilia Romagna region (North Adriatic Sea, Italy). Four studies estimated the magnitude and frequency of exploitation by people, and established how human exploitation varied in space and time. A manipulative experiment involving the removal of mussels, mimicking the impact of human harvesting, was carried out to identify the effects of extensive mussel exploitation. Recreational exploitation was a major recurrent disturbance. Hundreds of people visited defence structures for recreational fishing and to harvest a variety of invertebrates to be used primarily as food. Human exploitation was most intense during the spring and summer but relatively unpredictable at scales of days and hours. Exploitation was homogeneous among different locations, despite marked differences in the accessibility of the structures. Visitors to the structures were mainly local people. Harvesting of mussels was particularly disruptive for the assemblages, leading to depletion of mussel beds, opening of unoccupied space, patchiness in the assemblages, and favouring the development of macroalgae. The main types of macroalgae were green and filamentous algae, which are a nuisance for beach tourism in the area, and the invasive species Codium fragile ssp. tomentosoides. Effective management of human access to artificial habitats is essential, since recreational exploitation influences the distribution and structure of their associated assemblages, ultimately affecting the native characteristics of the areas.