Bouncing Boulders and Buoyant Seaweeds: developing indicators to tease human from natural disturbance on rocky intertidal shores

Impacts of unregulated activities within Marine Protected Areas (MPAs) may undermine the objectives for which the MPAs were instigated. UK governments have started investigating these impacts within their MPA network but... [ view full abstract ]

Impacts of unregulated activities within Marine Protected Areas (MPAs) may undermine the objectives for which the MPAs were instigated. UK governments have started investigating these impacts within their MPA network but gathering evidence of unregulated activities is particularly problematic when the activities have persisted prior and subsequent to MPA designation. The current research aims to develop a simple indicator of human impacts within protected areas. The ‘tool’ builds on previous monitoring trials that sought to monitor human impact whilst avoiding the need for surveillance of beach users within a Special Area of Conservation (SAC). Most disturbance of algal dominated boulder communities on sheltered, tide swept shores is assumed to be anthropogenic. Rocks are disturbed whilst collecting animals for food, bait or for recreational interest. If rocks are replaced in the wrong position their diverse under-boulder communities dry out and algae become trapped under the rock, creating an anoxic environment instead of a sheltered refuge for a variety of mobile species. This research uses novel accelerometer technology to differentiate between natural and anthropogenic disturbance. Counter to expectations, the presence of large algae causes drag on rocks that is sufficient to displace them. This unexplored form of natural disturbance on sheltered shores could become more prolific with increasing storm frequency and severity.  Policy makers and site managers must consider all sources of disturbance in a protected area, including from currently unregulated activities. A human disturbance indicator on suitable shores may reduce the risk of mistakenly attributing all disturbance to anthropogenic activities.