Role of settlement in determining the distribution and abundance of barnacles in a temperate mangrove forest

An increased understanding of the role of early life history stages in determining the distributions of benthic invertebrates require studies covering a wide range of habitats, and preferably multiple scales. For one of the more prominent invertebrate groups, intertidal barnacles, much of our existing knowledge is drawn from studies of rocky shores, with few studies from other habitats. Here, we describe the distribution of adults of the temperate barnacle Elminius covertus in mangrove (Avicennia marina) forests of southeastern Australia. We sampled E. covertus on pneumatophores over a large-scale (50–100 m) across the forests from the landward to seaward edges. We also described large scale patterns along the shore (also a scale of 100 m). At the seaward edge of the forest, on a small spatial scale, the vertical distribution of E. covertus on pneumatophores over 15 cm was also investigated. Settlement and recruitment were also estimated by allowing barnacles to settle on artificial substrata. The processes influencing the patterns of adults of E. covertus were very different over the two major scales in this study. At the large-scale, adult Elminius covertus were abundant at the seaward edges of forests, declining through the forest, and were absent at the landward sections of forests. Recruitment, measured over 1 month, and 1 week, matched this pattern, and settlement, measured over a single high tide, also matched the adult distributions. Along the shore, differences in abundance of adult barnacles were matched by variation in settlement and recruitment. Post-settlement mortality had little influence on this pattern. In contrast, on the small, vertical scale, barnacles were most abundant on the upper 5 cm of pneumatophores, and least common near the substratum. This vertical pattern reflected the pattern of recruitment after 1 month. Settlement, however, was different, with more settlement on the 5 cm of pneumatophores closest to the substratum. The distribution of recruits after 1 week was intermediate between settlement and recruitment after 1 month. The vertical pattern of adults is therefore determined by post-settlement mortality occurring during the first month after settlement.  1999 Elsevier Science B.V. All rights reserved. *Corresponding author. Present address: Faculty of Environment and Resource Studies, Mahidol University, Salaya, Nakhon Pathom 73170, Thailand. E-mail address: [email protected] (S. Satumanatpan) 0022-0981/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PI I : S0022-0981( 99 )00066-0 46 S. Satumanatpan et al. / J. Exp. Mar. Biol. Ecol. 241 (1999) 45 –66