Response of intertidal barnacles to air temperature: Long-term monitoring and in-situ measurements

A twenty-five year (1994–2018) survey at 10 rocky sites within Lough Hyne Marine Reserve (SW Ireland) showed that, despite considerable spatial and temporal patchiness, three barnacle species (Chthamalus stellatus, Semibalanus balanoides, and Austrominius modestus) declined in overall abundance in the early 2000s, particularly at three sites. There was no clear response of A. modestus or C. stellatus to the cold winters of 2010 and 2011. In 2004, however, S. balanoides declined suddenly, but showed a slight recovery after the cold winter of 2010 to maintain sparse populations in the lough, but remained abundant outside the lough. A fourth species, Chthamalus montagui, showed a different pattern, with wide fluctuations in abundance but no overall decline. Changes in the Atlantic Multidecadal Oscillation may have influenced the overall composition of barnacle populations. Rising maximum air temperatures, resulting in high body temperatures recorded for A. modestus even during mild days, are suggested to have impacted the barnacle populations as a result of the prolonged aerial exposure times caused by the lough's asymmetric tidal pattern.