Competition for space limits the expansion of biogenic tubeworm reefs

Competition for space is a critical driver of the distribution and dynamics of sessile marine organisms. This study investigated the competitive interactions between the honeycomb tubeworm Sabellaria alveolata and other sessile species, such as mussels, barnacles and articulated coralline algae, that dominate breakwaters along the Latium coast of the Northern Tyrrhenian Sea. We tested the hypothesis that removing dominant sessile organisms adjacent to S. alveolata patches would promote bioconstruction expansion. To test for the temporal generality of such a response, we performed 3 experimental trials differing in the timing of experimental removal of potential competitors of S. alveolata. In all trials, the percent cover of S. alveolata, estimated over about 1 yr, increased in cleared plots compared to unmanipulated control plots, where it was consistently almost null. The maximum expansion of sabellariid cover occurred where clearing preceded or coincided with the seasonal growth phase of S. alveolata. These findings highlight the role of competition in shaping the development of S. alveolata reefs and suggest its possible interplay with other temporally variable processes, such as natural life cycles and anthropogenic disturbances. They can also inform conservation strategies to preserve the ecosystem services provided by honeycomb worm reefs under increasing anthropogenic and natural environmental pressures.