MEPS 169:165-178 (1998)  -  doi:10.3354/meps169165

Comparison of the measurement and effects of habitat structure on gastropods in rocky intertidal and mangrove habitats

Michael W. Beck*,**

Institute of Marine Ecology, A11, University of Sydney, New South Wales 2006, Australia
**Present address: Coastal and Marine Program, The Nature Conservancy, 88 First Street, Suite 600, San Francisco, California 94105, USA

ABSTRACT: Ecologists have had little success in the development of a synthetic understanding of the effects of habitat structure on species, because structural complexity is measured differently in most studies and habitats. There were 3 main objectives of this study: (1) to measure and compare structural complexity between rocky intertidal and mangrove habitats, (2) to examine whether structural complexity affected the density, richness and size of gastropods in these habitats, and (3) to determine whether one index of structural complexity [e.g. fractal dimension (D) and chain-and-tape] best represented features of the habitat that affected gastropods. I used photogrammetric techniques to measure and to compare the effects of structural complexity in quadrats (1 m apart) nested within sites (10 m apart), shores (>1 km apart) and habitats (rocky intertidal and mangrove) in Botany Bay, Australia. All indices showed that complexity was different between quadrats just meters apart in both habitats and was greater in mangrove than in rocky intertidal habitats. Two lines of evidence indicated that variation in complexity affected the density of gastropods in rocky intertidal but not in mangrove habitats. First, the density of gastropods varied 4-fold between quadrats within habitats and, after gastropods were experimentally removed, a similar density and size distribution of gastropods recolonized quadrats in the rocky intertidal. Second, this density was correlated with structural complexity. D was most often correlated with density and thus best represented features of the habitat that affected gastropods. The measurement and effects of structural complexity can be compared between habitats, and these comparisons help elucidate the conditions in which habitat structure may exert strong effects on species.

KEY WORDS: Habitat structure · Fractal dimension · Rocky intertidal · Mangrove · Field experiment

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