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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13582

Effects of herbivorous gastropod grazing on the sedimentation and succession of subtidal macroalgal assemblages

Haruka Suzuki, Yuki Kubo, Eri Inomata, Yukio Agatsuma, Masakazu N. Aoki*

*Corresponding author:

ABSTRACT: The subtidal zone on cold temperate rocky coasts is an environment exposed to much less physical disturbance than the intertidal, and sediment deposition is continuous. Removal of this sediment by gastropod grazers is therefore presumed to affect the structure of subtidal algal communities. This was investigated by evaluating the grazing effects of the dominant herbivorous gastropod Omphalius rusticus by exclusion experiments in the field. Settlement plates of both exclusion and control treatments were placed every month from November, 2014, and immersed for a month. Algae colonized from May and tended to increase their biomass toward summer. No marked differences were observed in the algal composition of exclusion and control. Sediment deposition showed no apparent seasonal changes. Cumulative successional plates of both exclusion and control treatments were placed in November, 2014, and immersed for one to nine months. The colonization of algae started from February and the species number peaked earlier in the exclusion and later in the control. Sediment load and algal biomass were high from February to May in the exclusion, and from April to July in the control. Seedlings of Sargassum confusum were found in both plots from July. It is concluded that O. rusticus constantly removed sediments by its grazing activity and had a large impact on the formation of the macroalgal community by controlling sediment deposition. Its presence delayed the colonization of early-successional turf algal species, but did not affect colonization of late-successional canopy-forming algae such as S. confusum.