Temporal variation in early mortality of an intertidal barnacle

During the period following settlement to the substratum and preceding metamorphosis, dispersive larval stages of marine invertebrates must undergo a physiologically demanding metamorphosis, after which juveniles are exposed to new environmental conditions. Given that the intensity of biological and physical disturbance and larval physiological quality can vary over time, it would be expected that survival and growth would also vary among daily cohorts of settlers arriving to the benthic habitat. The objectives of this field study were to determine the extent to which daily cohorts of settlers of the barnacle Semibalanus balanoides differ in early post-metamorphic (i.e., juvenile) growth and survival, and to compare mortality of early juveniles and newly attached, pre-metamorphic individuals (i.e., cyprids). Mean mortality of all individuals 30 d after settlement differed significantly among the 5 daily cohorts examined, ranging from 29.9 to 70.2%. Mean mortality also differed significantly among the 5 daily cohorts for cyprids (range 15.3 to 43 %) and juveniles (range 7.1 to 30.8%), indicating that mortality of cyprids is generally at least as great as early juvenile mortality. Mean juvenile growth differed significantly among the 4 cohorts examined, with cohorts arriving during the beginning of the recruitment season exhibiting the fastest growth. These results support previous reports of significant variation in mortality and growth among daily cohorts of barnacles. It is proposed that temporal variation in cyprid mortality may weaken the strength of the relationship between larval abundance and recruitment for populations of marine invertebrates.