Barnacles have been recognized as fouling organisms for a long time. Adhering to ship hulls, piers, wharves and cooling-water pipes of power stations, they cause significant industrial damage. Nonetheless, barnacle nauplius larvae constitute a significant food source for the larvae and juveniles of various animal species in the coastal ecosystem. In order to evaluate the contribution of fouling barnacles to this larval output, every two weeks in 2008, the author examined the number of brooded eggs of barnacles settled on a test plate hung in the water in the Hyogo Canal, Kobe. Measurements of sea water temperature and salinity at the observation site, the density of barnacle nauplii in the plankton, and the number of settled barnacles on the test plate were made. The number of nauplius larvae hatched from the barnacles settled on the test plate was thereby estimated to be 100,000/cm² over the whole year.

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The introduced barnacle species Megabalanus coccopoma (Darwin 1854), which was originally described from the Pacific coast of Panama, was recently recorded in Tokyo Bay (Yamaguchi et al., 2009). Following this discovery, we reexamined previously published collection of preserved specimens of Megabalanus taken from lighted buoys in Tokyo Bay in 2004–2005 (Horikoshi & Okamoto, 2007), when M. coccopoma had not yet been recognized in Japan, to clarify whether this species was already present then or not. Among 24 buoys, M. coccopoma was found on 13 nearly throughout distributed the bay, while the indigenous congeneric species Megabalanus rosa (Pilsbry, 1916), the only megabalanid previously reported from these samples, was found on only 9 buoys in the southern part of the bay. Therefore, M. coccopoma must have been introduced to Tokyo Bay before 2004.

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