Impacts and interactions of two non-indigenous seaweeds Mazzaella japonica (Mikami) Hommersand and Sargassum muticum (Yendo) Fensholt in Baynes Sound, British Columbia




Pawluk, Kylee Ann

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This thesis examines the interactions of two non-indigenous algae, Mazzaella japonica and Sargassum muticum, where they co-exist and their impacts on native species in their recipient habitats. Field and lab experiments were conducted to determine if they impact native seaweed communities, marine invertebrates, and supralittoral regions. In situ studies conducted in areas where Mazzaella japonica exists without Sargassum muticum found that removal of M. japonica allowed for an increase of native seaweed abundance and richness growing in fully subtidal regions, but had no detectable impact on native seaweeds growing in intertidal regions. Additionally, at the intertidal site, removal of M. japonica resulted in the recruitment of S. muticum. In regions where the two non-indigenous seaweeds co-exist, removal of both non-indigenous seaweeds negatively impacted native seaweeds. The magnitude of this negative impact was greater in subtidal compared to intertidal regions. M. japonica removal had a greater impact on native seaweed recovery than did S. muticum removal in areas of co-existence. Removal of Mazzaella japonica also allowed for a significant increase in percent cover of Sargassum muticum at both sites where these two seaweeds co-exist. An increase in percent cover of M. japonica was found at the subtidal site when S. muticum was removed. Though both species increased when reprieved from competition with the other non-indigenous species, removal of M. japonica had a far greater influence on the increase in cover of S. muticum. This suggests that M. japonica is the dominant competitor in the ecosystem outcompeting S. muticum. Field surveys found Mazzaella japonica was the dominant wrack species washing up on beaches in Baynes Sound. Though Sargassum muticum is also a component of the wrack, it has a disproportionately large influence as a spatial subsidy on beach habitats. S. muticum decayed and decomposed at a faster rate than M. japonica and all native seaweeds tested except for Chondracanthus exasperatus. Additionally, S. muticum was colonized by significantly more invertebrates than either M. japonica or Fucus spp. Results from these studies are intended to provide information for resource managers making policy decisions regarding the fate of these two non-indigenous species.



Non-indigenous seaweeds, Competition, Sargassum muticum, Mazzaella japoinca, Wrack, Multiple invaders