Connectivity and population repatriation: limitations of climate and input into the larval pool

We used climate-induced variation in fecundity of the barnacle Semibalanus bal- anoides to test the hypothesis that variation in adult input to the larval pool is a driver of connec- tivity among adult populations of coastal marine invertebrates. We predicted that cold winters will lead to high reproductive output and high recruitment by S. balanoides, while warm winters will result in low reproductive output and low recruitment. Following the cold winter of 2009 to 2010, larval recruitment was exceptionally high (>6 cm 2 ) in Southwest England, resulting in a range expansion of over 100 km. The following winter was also cold, and recruitment was again high. The winter of 2011 to 2012 was warm, and recruitment was low (~1cm �2 ) throughout Southwest England. These data indicate that recruitment and population connectivity are strongly linked to adult input to the larval pool. We analyzed winter temperature variation over the past 3 decades and found that warm winter temperatures over the 13 yr prior to this study likely led to frequent reproductive failure and the decline of S. balanoides in Southwest England. Continued warming in this region is likely to permanently exclude S. balanoides from this portion of its geographic range. This study illustrates an important role of adult input into the larval pool in controlling pop- ulation connectivity in open marine ecosystems and also implicates climate variation in determin- ing the range limit of a significant component of coastal ecosystems in Europe.