MEPS 392:111-122 (2009)  -  doi:10.3354/meps08247

Facilitation of molluscan assemblages in mangroves by the fucalean alga Hormosira banksii

Melanie J. Bishop1,3,*, Tara Morgan1, Melinda A. Coleman2, Brendan P. Kelaher1,  Lyndle K. Hardstaff1, Robert W. Evenden1

1Department of Environmental Sciences and Institute for Water and Environmental Resource Management, University of Technology Sydney, PO Box 123, Broadway, Sydney, New South Wales 2007, Australia
2Centre for Marine Bio-Innovation, University of New South Wales, Sydney, New South Wales 2052, Australia
3Present address: Department of Biological Sciences, Macquarie University, North Ryde, Sydney, New South Wales 2109, Australia

ABSTRACT: The fucalean macroalga Hormosira banksii facilitates diverse rocky intertidal communities. Along the east coast of Australia, the alga can also persist in mangroves as a free-living form trapped amongst pneumatophores. We investigated (1) whether the alga has an effect on molluscan species richness and abundance in mangroves similar to that on rocky shores, and (2) whether, in mangroves, the source (phenotypically distinct estuarine or rocky shore populations) of H. banksii influences the outcome of its interspecific interactions. Sampling of 3 rocky shore and 3 mangrove sites along the east coast of Australia revealed that patches of H. banksii consistently supported a greater species richness of molluscs than adjacent substratum. Whereas the alga increased the abundance of molluscs in the mangrove forest, it had no effect or decreased molluscan abundance on the rocky shore. Transplant of H. banksii from rocky shores and estuarine tidal flats into the mangrove indicated that the source of the algae influenced the magnitude of effects. Although all algae enhanced molluscan abundance and species richness, estuarine H. banksii, which had larger vesicles and a longer thallus, supported more molluscs of more species than rocky shore H. banksii. These results support the growing consensus that the influence of foundation species at the community level is dependent on environmental conditions. As human activities place increasing pressure on coastal ecosystems, it will be important to understand the mechanisms and conditions that determine community-level effects of foundation species so that biodiversity may be conserved.

KEY WORDS: Facilitation · Foundation species · Macroalgae · Mangroves · Molluscs · Rocky shore

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Cite this article as: Bishop MJ, Morgan T, Coleman MA, Kelaher BP, Hardstaff LK, Evenden RW (2009) Facilitation of molluscan assemblages in mangroves by the fucalean alga Hormosira banksii. Mar Ecol Prog Ser 392:111-122

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