Heterogeneous shell growth of the neustonic goose barnacle Lepas anserifera

Abstract

Floating materials of both natural and anthropogenic origin affect marine ecosystems and human economic activities. Although the tracking of floating materials is important to manage the economic risks, it is difficult to trace them back to the events of origin, such as tsunamis and underwater volcanic eruptions. The gooseneck barnacle Lepas anserifera, a rapid colonizer in pelagic environments, is a potential “natural logger” of floating materials. In this study, we performed temperature-controlled culture experiments and growth line staining in the laboratory to quantify the growth increments of shells (scutum and tergum) consisting the capitulum of L. anserifera separately, and to examine the effects of the temperature on their growth. Following calcein staining, the growth lines of L. anserifera were visualized under a fluorescent microscope, and gross (capitular length and width) and individual (scutum and tergum) shell growth were compared. Shells grew in twice as much in the capitular length direction than in the capitular width direction owing to the larger growth increases in the scutum than in the tergum. Growth increments were unaffected by temperatures in the range from 20°C to 30°C, although the growth appeared to slow down in September and October compared with August. The stable oxygen isotope composition (δ18O) of the shells represented the water temperature as previously known, and the present results showed that 18O enriched in scutum than tergum in most cases. Further understanding for the biomineralization process of barnacles is required for the precise application of environmental proxies in barnacle shells.