A Shift in Feeding Behavior from the Juvenile to Adult in the Giant Acorn Barnacle Balanus Nubilus Darwin with Observations on the Develepental Time Course of Larvae
Hart, Alfred K.
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Barnacles exhibit diversified forms of cirral fan behavior in food filtering and respiration. The repertoire of cirral fan behaviors for adults of a number of species has been associated with their physiology, ecology, and phylogeny. Feeding behaviors of juveniles have not been significantly investigated with the exception of two species of pedunculate barnacles, Pollicipes, that exhibit behaviors distinct from adults and until recently, undescribed for the species. The Balanidae exhibit some of the most diverse cirral behaviors. This study was conducted to investigate the disparity between feeding behaviors of juveniles and adults in Balanus nubilus. Specimens of varied cirral fan length, from recently metamorphosed juveniles to large adults, were collected and observed in a flow tank under six treatments: three seawater flow rates and in the presence or absence of food. Observations were made of cirral behavior types, total active time, and cirral activity rate, measured as the number of repetitive cirral movements per minute. Total active times and mean rates of cirral activity were regressed against cirral fan length. Cirral activity and total activity time decreased with increased cirral fan length. Feeding strategies of juveniles differed from adults. Juveniles were found to exhibit cirral behaviors that prior to this study were undescribed for this species, as well as a form of backward beating previously undistinguished among barnacles. In addition to studying feeding behaviors of barnacles, biologists have dedicated considerable effort to the developmental time course and physiology of the naupliar stages. For many species, including Balanus nubilus, little information is available on the developmental time course of the six naupliar and non-feeding cyprid stages. Larvae of Balanus nubilus were cultured from eggs of gravid adults. Subsamples collected every other day elucidated a developmental time course that was longer than others of the genus.