Meeting Abstract
The invasive slug Arion rufus is a prevalent garden pest along the Pacific Northwest coast, but the extent to which this slug affects local native grassland ecosystems is unknown. No native pulmonate in this ecosystem attains even an appreciable fraction of the size of A. rufus, so this newcomer may be an important addition to the herbivore/detritivore food webs. Previous work has shown that slugs can impact plant diversity and biomass production in grasslands, and that in forest ecosystems A. rufus limits plant growth through herbivory, but accelerates nutrient cycling. This study, conducted on San Juan Island, Washington State, sought to understand the impacts of the feces, mucus, and herbivory of A. rufus on biomass production of the annual ryegrass Lolium multiflorum. We exposed seedlings (100 per pot) in small isolated mesocosms to one of three treatments: live slugs, slug feces only, or no slugs. After a month of applying treatments, there was no significant difference across any of the treatments in seedling germination, seedling survival rate, or above- or below-ground biomass production (either wet or dry weight). Surprisingly, despite observable seedling herbivory within the first few days of germination in the live slug treatment, there was also no significant difference among treatments in blade length or average weight per blade at the conclusion of the experiment. These findings suggest that, despite processing large amounts of local primary production, the excrement contributed by A. rufus did not fertilize the surrounding ryegrass in a way that affected the growth of the plants.
