Strongylocentrotus purpuratus herbivory

There has been over a 90% loss of the Northern California kelp forest canopy from 2014 to 2019. Many factors have contributed to the kelp forest decline including climate change, marine heat waves and the loss of the purple urchin's main predator, the sea star (due to sea star wasting disease), which has shifted many lush kelp forests into urchin barrens. I chose to investigate the Strongylocentrotus purpuratus, the purple urchin, herbivory of Nereocystis luetkeana, bull kelp. Remnant bull kelp patches along the coast often correlate with areas of freshwater input, lower salinity. Here it appears that the kelp is not under the same pressure of urchin herbivory as the kelp out in higher salinities. To test if salinity is a potential factor limiting urchin herbivory I fed bull kelp to purple urchins at different controlled salinities and recorded how much consumed after three days. I found a significant decline in herbivory rates of the purple urchins after the salinity dropped below 30 ppt. Establishing lower salinity as a factor in reducing urchin herbivory is important when informing restoration efforts and where kelp outplants could most successfully thrive.