The legacies of land-clearance and trophic downgrading accumulate to affect structure and function of kelp forests

Aotearoa New Zealand is the last major landmass settled by people, and therefore provides a recent record of ecological legacy effects in the coastal zone. Large-scale land clearances of forests accelerated over the last century, affecting the concentration of suspended sediments, light environment and nutrient composition on rocky reefs, and consequently the distribution, abundance and composition of algal forests. Environmental effects were compounded in many places by overfishing and long-term declines of large predatory species, often leading to proliferation and extensive grazing by sea urchins. Here we examine these processes in three biogeographic regions that have been differentially affected by ecological legacy effects. The study was based on the depth-specific associations between sea urchins (Evechinus chloroticus) and the common kelp (Ecklonia radiata) from multiple sites within each region, some of which were sampled over two decades within no-take marine reserves and in a...