Marine Biology


Thornber, Carol

Advisor Department

Biological Sciences




Grateloupia; Hemigrapsus; Littorina; community ecology; invasive


Invasive species have the ability to outcompete natives, and can create a monoculture if not mitigated by herbivores or some other mechanism. Limited information exists on the ecology of the invasive macroalga Grateloupia turuturu and how it is impacted by herbivores. Using laboratory mesocosm experiments, we investigated the ability of two invasive herbivore species common in Rhode Island, the snail Littorina littorea and Asian shore crab Hemigrapsus sanguineus, to control Grateloupia populations. In the first trial, Grateloupia was provided to a single herbivore (either Littorina or Hemigrapsus) or both herbivores together. Grateloupia controls were in the same mesocosms as each treatment, but were separated by a mesh partition to allow water flow and account for possible facilitation by herbivore presence. Mesocosms were kept at 13°C and at 0, 2, 4, and 6 days, the algae was weighed and water samples were taken. Preliminary results indicate that Littorina do indeed graze on Grateloupia, with an average decrease in mass of 44.6% after 6 days. There was no significant change in mass of Grateloupia in the presence of Hemigrapsus only or with Littorina and Hemigrapsus together. Future trials will include two common species of marine macroalgae along with the Grateloupia, to investigate herbivore feeding preference when exposed to multiple food choices. The ultimate results of these trials are intended to indicate the success of the continued invasion of Grateloupia in Rhode Island waters, and predict the role of invasive herbivores in controlling Grateloupia populations.