Meeting Abstract
Climate change is altering the distribution and abundance of marine organisms. Understanding the mechanisms responsible for driving these changes can be challenging due to the decade to century long time scales. The shorter time scale of range shifts due to extreme events makes them more tractable. In the 1960s the barnacle Semibalanus balanoides was present along the USA east coast south to Cape Hatteras, NC (35°N). Since then the southern range limit in this region has retracted poleward 350 km to Lewes, DE (38.5°N). Following the extremely cold winter of 2014/2015 recruits were present between Lewes and Cape Hatteras. We tested whether temperature limits to reproduction or temperature limits to survival prohibited colonization of S. balanoides within its historical range, and if the observed pattern of recolonization was dependent on stepping-stone dispersal in consecutive cold winters. Models of larval dispersal with a temperature-dependent competency window predicted dispersal was possible from currently established populations to the southern limits of recruitment observed in 2015. Successful reproduction was likely possible just north of Cape Hatteras in all years since the 1960s. All recruits in monitored quadrats throughout the region of range re-expansion died. During surveys in March 2016 adult S. balanoides were present at a heavily shaded site near Cape Hatteras. By July 2016 these adults were covered in Chthamalus recruits. Experiments are currently in progress to determine whether competition eliminates S. balanoides from shaded microhabitats where temperatures are not lethal. Low post-settlement survival most likely contributed to the retraction of S. balanoides since the 1960s. It remains to be seen if competition further constricts the range of S. balanoides in this region.
