Spatial patterns of barnacle settlement in central Chile: Persistence at daily to inter-annual scales relative to the spatial signature of physical variability

Recruitment patterns of coastal species with complex life cycles are heavily influenced by physical variability in the coastal ocean. Spatial and temporal patterns of variability in rates of larval settlement may provide clues as to the processes that drive their transport and onshore delivery, as well as variation in the supply side of population dynamics. Over 3 consecutive seasons (2006–2008), the settlement of three intertidal barnacles (the chthamaloids Jehlius cirratus and Notochthamalus scabrosus, and the balanoid Notobalanus flosculus) was monitored daily at 5 to 6 sites spread over ca. 10 km around the bay of Cartagena in central Chile, and over periods of 48, 71 and 53 consecutive days that encompassed the settlement season of these species. This sampling effort yielded settlement data with an unprecedented combination of temporal resolution and spatial coverage, which allowed us to assess and compare: (1) spatial patterns of settlement and their persistence over scales of days within each season, (2) inter-annual variation in pattern persistence, and (3) the relationship between such variation and inter-annual changes in spatial patterns of sea surface temperature (SST) variability over synoptic and high-frequency scales. While on average the spatial pattern of settlement in chthamaloids became less persistent from 2006 to 2008, the settlement pattern of N. flosculus across sites remained persistent regardless of inter-annual changes in mean settlement rates. Within seasons, the spatial patterns of settlement of N. flosculus were persistent over scales of at least 15 days, whereas for chthamaloids a spatially ordered pattern of settlement in 2006 disappeared in subsequent years. Together, these results suggest that spatially structured processes that drive larval transport, and which can vary from year to year, may have played a greater role in shaping settlement patterns of chthamaloids versus balanoids. Synoptic-scale SST variability (i.e. days) exhibited spatial structure that was highly persistent within all three seasons. Although high-frequency SST variability (i.e. hours) has been associated to onshore larval transport within the study region, its among-site patterns were not as persistent as the daily ones. Since neither synoptic-scale nor high-frequency processes shaping patterns of physical variability are sufficient to explain inter-annual variability in patterns of larval settlement, more complex physical–biological interactions must be examined. We suggest that inter-annual changes in the pattern of wind forcing relative to local topography, and the thermal structure that results from such interaction, might be related to whether the spatial structure of barnacle settlement is persistent or fluctuating within a given season. We discuss the limitations of inferences that can be made regarding transport processes from time series of larval settlement, and the insights that can be gained by focusing on the variability of spatial patterns rather than temporal changes at individual sites.