The importance of substratum and elevation in recruitment and persistence of ulvoid algal blooms on rocky intertidal shores of the southern Korean coast

Patterns in the recruitment, distribution, and persistence of three Ulva species, which can form green tides, were investigated in relation to surface roughness using artificial substrates on intertidal rocky shores of the southern coast of Korea. The vertical distributions of Ulva pertusa, Ulva linza, and Ulva compressa were well separated: U. compressa usually dominated in the upper zone and U. pertusa and U. linza in the lower zone. Ulva pertusa recruitment was observed during autumn, when inorganic nitrogen concentrations in the surface water column were highest. However, the recruitments of U. linza usually occurred during early winter and spring and that of U. compressa during summer-autumn. Ulva pertusa showed highest settlement on rough surfaces in both zones, whereas this pattern only appeared in the upper zone for U. linza and U. compressa. These results indicate that settlement patterns may be affected by desiccation in the upper zone and waves in the lower zone. Once blooms occurred, U. pertusa persisted for about twice as long as the other two Ulva species, suggesting that U. pertusa played an important role in community change. This is the first documentation of persistence periods related to recruitment in bloom-forming green macroalgae.