MEPS 326:99-113 (2006)  -  doi:10.3354/meps326099

Effect of grazing on coralline algae in seasonal, tropical, low-shore rock pools: spatio-temporal variation in settlement and persistence

Tak-Cheung Wai, Gray A. Williams*

The Swire Institute of Marine Science, Department of Ecology and Biodiversity, The University of Hong Kong, Pokfulam Road, Hong Kong, SAR, China

ABSTRACT: Low-shore rock pools in Hong Kong are dominated by crustose coralline algae (CCA) all year round. Experiments manipulating grazer access to new surfaces and those with established CCA were used to investigate the spatial and temporal effects of grazers on establishment and persistence of CCA. During establishment, CCA were always the first macroalgae to recruit to new surfaces. Predictable algal colonization patterns were observed, although the extent and timing varied spatially (between pools) and temporally (with season and year). Grazing was the primary factor controlling the dominance of the CCA in low-shore rock pools, and seasonal differences in algal composition were only pronounced in the absence of grazers. On new surfaces, where grazers were excluded, the settling CCA were overgrown by competitively superior brown crustose algae (Ralfsia spp.) in summer and by non-crustose macroalgae (Ulva spp., Enteromorpha compressa, Hincksia mitchelliae and/or Colpomenia sinuosa) in winter. On CCA-colonized surfaces, E. compresa was, however, the dominant macroalga in winter in the absence of grazers. As a result of thermal stress in summer, the established CCA were commonly bleached, and new patches of bare surface were subsequently released. Such physical disturbance, hence, re-initiated colonization processes. The rapid re-colonization of CCA on new surfaces by lateral growth and new settlement suggests that CCA are resilient in nature, which results in them being the dominant macroalgae in the low-shore rock pools, all year round, in the presence of grazers.

KEY WORDS: Crustose coralline algae · Herbivory · Settlement · Summer heat stress · Persistence · Spatial and temporal variation

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