Massive recruitment of the barnacle Semibalanus balanoides in the Clyde Sea (Scotland, UK) in the spring of 2000

In April 2000 a massive recruitment of the barnacle Semibalanus balanoides was observed in the Clyde Sea. At one location 700 cyprids l(-1) of this species were recorded. This is similar to3500 times more abundant than previously recorded, and resulted in metamorphosis of some cyprids whilst still in the plankton, as well as massive settlement, with recruits found on adults and in the splash zone. The maximum density recorded was 109 settlers cm(-2). Over the next 60 d mortality averaged 85%, resulting in a mean density of 8.4 recruits cm(-2) in June 2000. Recruitment varied spatially at the kin and in scale (site, shore height) but there was no evidence that it was affected by the presence of adult conspecifics.