Patterns of adult abundance vary with recruitment of an invasive barnacle species on Oahu, Hawaii

Abstract

The ability of non-native species to establish and spread is an interplay between the characteristics of the recipient ecosystem (e.g., biotic resistance) and the characteristics of the invading species (e.g., if it is a habitat generalist, fast-growing, highly fecund). In the Hawaiian Islands, the successful establishment and high impacts of many non-native species have been attributed to a disjunct flora and fauna that results in resources that can be readily exploited. Along these lines, the speed with which the Caribbean-Atlantic barnacle Chthamalus proteus became widespread in Hawaii has been attributed to the availability of settlement space in the intertidal zone. I investigated the relative importance of competition and recruitment in regulating the abundance of C. proteus at three sites on the island of Oahu. Recruitment of C. proteus and other barnacle species mirrored adult abundance. Competition with adult barnacles did not appear to be a factor at two sites. At a third site, where recruitment was the highest, competition between C. proteus and an early invader, Amphibalanus reticulatus, in the form of space pre-emption was occurring, apparently mediated at least in part by the preference of A. reticulatus to settle near conspecifics. C. proteus and the native barnacle Nesochthamalus intertextus displayed no such settlement preference. Earlier studies linked differences in recruitment rates of barnacles and other invertebrate species on Oahu to differences in circulation patterns that bring offshore waters into shore at some sites and hold near-shore water flowing out of lagoons and harbors close to shore in others. The present study adds to a growing body of work that suggests that while the relative importance of pre-settlement vs. post-settlement factors to invasion success varies with location, knowledge of local oceanographic conditions could help predict the spread of non-native marine species.