Direct Growth Measurements of Two Deep-sea Scalpellid Barnacles, Scalpellum stearnsii and Graviscalpellum pedunculatum.

: Yoichi Yusa, Natsumi Yasuda, Tomoko Yamamoto, Hiromi Kayama Watanabe, Takuo Higashiji, Atsushi Kaneko, Kazuki Nishida, and Jens T. Hoeg (2018) Little is known about the growth rates of invertebrates living in ordinary deep-sea habitats such as continental slopes. Thus, the growth rates of two species of the deep-sea scalpellid barnacles, Scalpellum stearnsii and Graviscalpellum pedunculatum, were studied in two aquaria (at Nara and Okinawa Churaumi, Japan). In addition, growth of an S. stearnsii individual after 1 year of deployment was measured in the field. Overall, adult individuals of both species showed slow growths over 8 months (at Nara) and 2 years (at Okinawa) of rearing (e.g., at Nara: 2.0 ± 3.6 μm d-1 for S. stearnsii and 5.9 ± 2.7 μm d-1 for G. pedunculatum; mean ± SD). In contrast, growth rates of juvenile S. stearnsii at Nara were greater (15 ± 7.7 μm d-1). The in situ growth rate of the adult S. stearnsii (3.4 μm d-1) was greater than the average, but within the range of the rates of similar-sized individuals recorded in aquaria. Compared with other pedunculate barnacles, both species show small growth rates typical for deep-sea animals.