Wind-driven diurnal temperature variability across a small bay and the spatial pattern of intertidal barnacle settlement

Abstract

Temperature variability under different wind conditions and its association with the spatial pattern of settlement of three intertidal barnacles – the chthamaloids Jehlius cirratus and Notochthamalus scabrosus, and the balanoid Notobalanus flosculus – were studied across Cartagena Bay, located in the upwelling region of central Chile. During days of strong winds, the diurnal signal in surface temperature at the protected end of the bay (site CTGN) was attenuated and decoupled from the northern sites (ECIM and PCHC) which are directly exposed to wind forcing, suggesting that wind intensity drives shifts in the relative importance of physical transport processes across the bay. Overall, the mean settlement rates of both chthamaloids were higher at PCHC, whereas N. flosculus settled at higher rates in CTGN. Under strong wind conditions, settlement rates of both chthamaloids decreased at the northern sites, while the settlement of N. flosculus reached minima at all three sites. Moreover, the effect of wind stress on the spatial pattern of settlement across the bay differed between species. A significant and positive correlation between the spatial heterogeneity of settlement and maximum daily wind stress – used as a metric for the intensity of the afternoon sea breeze – was found only for J. cirratus. It is concluded that daily changes in wind stress have a strong effect on the spatial pattern of diurnal temperature fluctuations, and on the spatial pattern of barnacle settlement around the bay. Such association emerges from the effect of wind on near-shore circulation and its differential modulation of thermal structure around an open embayment and, by extension, on the patterns of larval transport and onshore delivery to sites located at extremes of the bay, which probably is common in other bays with similar characteristics.