Ulva and Gigartina

Based upon figure 1 the effect of Ulva on Gigartina is a positive effect following the facilitation model. A facilitation model means that early colonists modify the environment so that it is more suitable for late successors and less suitable for other early successors. The Gigartina is a late species and when the Ulva is present then the number of Gigartina increases over time. When Ulva is removed the Gigartina levels are consistently low throughout both years.