Biogeographic Variability in the Value of Mussel Beds as Ecosystem Engineers on South African Rocky Shores
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Ecological engineers have important effects on biodiversity because they often increase habitat complexity and moderate environmental conditions, implying that their influence on associated fauna will vary across gradients of environmental stress. To test this, we quantified the positive effects of mussel beds on associated benthic communities around the entire South African coastline (~3500 km). We hypothesised that molluscan assemblages would show stronger affinities to the presence of mussel beds with increasing levels of heat-stress. Biomimetic loggers used to characterise thermal properties within and outside mussel beds found that solitary mussels experienced significantly greater daily maximum temperatures than mussels within beds across all locations. However, the magnitude of such differences did not appear to vary with latitude or time of year but rather was strongly influenced by biogeographic region. Differences in the abundance, diversity and community structure of molluscs within and outside mussel beds showed similar biogeographic variability, with differences in total molluscan abundances being most pronounced along the cool temperate west coast during summer and least pronounced along the warm temperate south coast during winter. Greater affinity of molluscan assemblages for mussel beds within cooler biogeographic regions suggests that evolutionary history and/or other abiotic factors may be the primary cause for the stronger influence of mussel beds on the west coast. This highlights the complex, context-dependant nature of ecosystem engineering and the varying degrees to which associated organisms affiliate with these biogenic structures. Such findings have important implications for the use of ecosystem engineers as umbrella species in ecological conservation.
Keywordsbody temperatures ecosystem engineers mollusc assemblages mussel beds Mytilus galloprovincialis Perna perna rocky intertidal shore South Africa thermal stress
We would like to thank Jaqui Trassierra, Morgana Tagliarolo, Eleonora Puccinelli, Bruce Mostert, Aldwin Ndhlovu, Carlota Fernandez Muniz, Martinus Scheepers and Elizabeth Lathlean for assistance in the field; Gwen Johnson for her considerable administration skills and Elizabeth Lathlean for comments on earlier versions of the manuscript. This work was funded by a National Research Foundation Postdoctoral Fellowship to J. A. L., a Rhodes University Research Council Grant and by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation.
- Anderson MJ. 2005. PERMANOVA: a FORTRAN computer program for permutational multivariate analysis of variance. Auckland: Department of Statistics, University of Auckland.Google Scholar
- Clarke KR, Gorley RN. 2006. PRIMER v6: user manual/tutorial. Plymouth, UK: PRIMER-E.Google Scholar
- Newell RC. 1979. Biology of intertidal animals. Faversham, Kent: Marine Ecological Surveys.Google Scholar
- Stephenson TA, Stephenson A. 1974. Life between tidemarks on rocky shores. San Francisco: W.H. Freeman.Google Scholar