The population dynamics of Balanus rostratus (Cirripedia: Thoracica) in Shizugawa Bay, northern Japan

Abstract

Benthic adult individuals and planktonic larvae of the barnacle Balanus rostratus were collected monthly from April, 2003, to March, 2005, in Shizugawa Bay, Miyagi Prefecture, Japan. The adult barnacles, with a maximum base diameter of 20-60mm, exhibited an increase in gonad somatic index from October to December, and breeding individuals appeared in December and January. The occurrence of nauplius larvae of B. rostratus was restricted to winter months, from January to March, and this was followed by the recruitment of small juveniles of 1-4mm in maximum base diameter to the rocks. Under natural conditions, slow growth was observed in newly settled individuals in spring, with the mean base diameter only increasing to 7mm by December-January; however, relatively high growth rates were observed in young barnacles transplanted to plastic plates and further cultured in Shizugawa Bay. The mean maximum base diameter of of B. rostratus may be attributable to differences in environmental conditions or size-dependent mortality. Under natural conditions, the number of newly settled barnacles decreased drastically after May and they almost disappeared until January during the experimental period. The cause of this decrease may be due to post-settlement mortality biased towards larger individuals (e.g., size-selective predation), which may result in underestimation of the growth rate of young barnacles in the natural population. During the two-year investigation, few individuals recruited into size classes over of 10mm in maximum base diameter because of the low survival rate. Although B. rostratus is regarded as a long-lived species with a high survival rate among its large individuals (>20mm in maximum base diameter), the high mortality of young barnacles has the potential to lead the population to extinction. Thus, the intermittent occurrence of a dominant year class may be a strategy for sustaining the population.

Growth, feeding, and larval density of <i>Balanus rostratus</i> in Ofunato Bay, northern Honshu, Japan, compared with those in adjacent Mutsu Bay, Okirai Bay and Shizugawa Bay

“…The settlement depth for Balanus rostratus was suggested to be 10 m or deeper in Mutsu Bay (Kado, 2009b), while Nakanishi et al (2003) reported that the settlement depth was 20 and 30 m in the same bay and that the settlement at 30 m was more frequent. In Shizugawa Bay, very dense settlement was reported on the bedrock at depths of 8-13 m (Yamauchi et al, 2007). In Ofunato Bay, the barnacles occurred at 4-5 m on the quay wall that extended down to 6 m. In May, later stage nauplii were mostly observed in the lower layer (6-18 m), and the density of cyprids was also high below that, suggesting that this species might avoid shallow water depths.…”

“…In Okirai Bay, the basal diameters of the 1996 cohort settled on PVC panels in Mutsu Bay and then transplanted to Okirai Bay in June of the same year were approximately 38.7 mm at 5 m depth and 38.3 mm at 10 m depth, respectively in January 1998 (Kado et al, 2009a). In Shizugawa Bay, the basal diameters of the 2004 cohort of the natural population settled on seafloor rocks and barnacle shells at 1 m and 15 m depth were 25.8 mm and 27.0 mm in April of the following year (Yamauchi et al, 2007).…”

“…The time of settlement of Balanus rostratus is from October to December in Amurski Bay, Vladivostok Ovsyannikova, 1998, 1999), from January to March in Otsuchi Bay, north of Ofunato Bay (Kado et al, 1981), and from February to April in Shizugawa Bay, south of Ofunato Bay (Yamauchi et al, 2007). Although the settlement time has not been investigated in detail, it is suspected to be from early January to mid-March in Mutsu Bay (Nakanishi et al, 2003) and from March to May in Ofunato Bay (present study), considering the periods of appearance of cyprid larvae in each locality.…”

“…Ecological studies on this species include reports on its reproduction in the Bay of Emar, a branch of Peter the Great Bay in the northern Sea of Japan, and on its tolerance to organic pollution and anaerobic conditions (Korn, 1985;Ovsyannikova, 1998, 1999). In Japan, there have been investigations on growth, reproductive cycle, and time of lar-val appearance and distribution in Mutsu Bay (Kado, 1996;Nakanishi et al, 2003;Kado et al, 2009b), on growth, reproductive cycle and diet in Okirai Bay, Iwate Prefecture (Kado et al, 2009a), and on population dynamics in Shizugawa Bay, Miyagi Prefecture (Yamauchi et al 2007). In Mutsu Bay, where this species is cultivated, it is a phytoplankton-or detritus-feeder, reaching a basal shell diameter of more than 40 mm two years after attachment, and has an annual reproductive cycle, with mating completed by late November, followed by larval emergence in December (Kado et al, 2009b).…”