Variation in mussel and barnacle recruitment parallels a shift in intertidal community structure in the Cook Strait region of New Zealand

Abstract

Recruitment influences populations and communities of marine organisms to varying degrees and across a range of spatial scales. We hypothesised that recruitment plays a role in maintaining different intertidal invertebrate assemblages between two nearby locations in New Zealand (Wellington Harbour and the south coast), long reported to have dramatically different communities (with greater cover of sessile invertebrates in the Harbour). Sites in Wellington Harbour were hypothesised to have higher monthly recruitment rates of mussels and barnacles and greater barnacle colonisation after 1 year. Surveys were conducted to quantify community differences. In Wellington Harbour, the mid-intertidal zone was dominated by the mussel Mytilus galloprovincialis and the barnacle Chamaesipho columna and the high intertidal zone by C. columna. In contrast, on the south coast mussels were almost completely absent from both tidal heights and barnacles (predominantly Chamaesipho brunnea) were sparse. In the high zone, monthly recruitment and long term colonisation (over 1 year) of barnacles was much greater in the Harbour; in the mid-intertidal zone, mussel recruitment was up to two orders of magnitude greater in the Harbour than the south coast. Species-specific recruitment patterns differed between the locations, however and were consistent with those of adult abundance.