Same Stone, Different Outcomes: Marine Communities on Engineered vs. Natural Rock Shores

The effort to protect coastal property and infrastructure from storm damage, erosion, and sea level rise has resulted in increased construction of coastal protection structures (CPS) worldwide. Researchers around the globe have found that the marine communities living on CPS differ from those living on natural rock outcroppings in the same area. We conducted a classic disturbance experiment to investigate possible differences in marine organism response and community assembly between natural and human-constructed rocky intertidal habitat along the Massachusetts coast. The one-year study used naturally occurring rock shores and human-made granite seawalls with both wave-exposed and wave-protected areas. Significant differences in both the amount of substrate utilization and the composition of the colonizing marine community on the natural and human-engineered habitats were evident one year after the clearing disturbance. The natural rock experimental plots had a higher mean proportion of macroalgal and marine invertebrate cover overall, and regrowth was dominated by red and brown algal species. Human-engineered seawalls evidenced significantly lower mean cover proportion and dominance of green algal species. Wave exposure also had a significant effect, though less than substrate type. These experimental results raise the possibility that ongoing expansion of CPS along the Gulf of Maine and New England coast could alter coastal marine ecosystems and, over time, could have far-reaching impacts on the region’s marine biodiversity and ecosystem functioning