MEPS 246:291-305 (2003)  -  doi:10.3354/meps246291

Determination of abundance and distribution of an intertidal barnacle: settlement or post-settlement mortality?

Carolyn J. Jeffery*

Centre for Research on Ecological Impacts of Coastal Cities and Institute of Marine Ecology, Marine Ecology Laboratories, A11, University of Sydney, Sydney, New South Wales 2006, Australia Present address: 13 Rhonda Avenue, Frenchs Forest, Sydney, New South Wales 2086, Australia

ABSTRACT: The honeycomb barnacle Chamaesipho tasmanica Foster and Anderson has great variation in abundance and distribution in intertidal areas at Cape Banks, New South Wales. This study was initiated to explain these observed patterns by investigating the relative effects of settlement and post-settlement mortality on populations of C. tasmanica. The relative importance of stages of the life history in determining the demography of adult populations was interpreted by simultaneous studies of adults and of juveniles from July 1989 to July 1994. It was found that settlement was integral to the demography of these barnacles; the alternative model that post-settlement mortality determined the distributions and abundance of juveniles and adults was discounted by experimental tests. Spatial patterns of post-settlement mortality of juveniles did not match spatial patterns of adult mortality. Conversely, despite great post-settlement mortality of juveniles, especially when the limpet Cellana tramoserica was present, spatial patterns of juveniles were retained by adults. Although there were isolated incidences of intense mortality by the whelk Morula marginalba, larval processes primarily determined the numbers of C. tasmanica at Cape Banks. Moreover, recruitment each year was not sufficient to maintain populations of adult barnacles; hence, numbers at Cape Banks were observed to decrease from 1989 to 1993 at all sites and heights studied. This study therefore emphasized the importance of the juvenile stage in maintaining populations of C. tasmanica.

KEY WORDS: Barnacles · Chamaesipho tasmanica · Settlement · Cellana tramoserica · Post-settlement mortality · Intertidal

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