Life cycles of the rhizocephalan Boschmaella japonica Deichmann & Høeg, 1990 (Cirripedia: Chthamalophilidae) and its host barnacle Chthamalus challengeri Hoek, 1883 (Cirripedia: Chthamalidae)

Although parasitic castration is widespread among rhizocephalan barnacles, Boschmaella japonica Deichmann & Høeg, 1990 does not completely sterilise the host barnacle Chthamalus challengeri Hoek, 1883. As little information is available on the relationships with the host in “barnacle-infesting parasitic barnacles” (family Chthamalophilidae), we studied the life cycles of both B. japonica and C. challengeri and the effects of the parasite on the host reproduction. Specimens of C. challengeri were collected from an upper intertidal shore at Shirahama, Wakayama, western Japan from April 2017 to September 2018 at 1–3 mo intervals. We recorded the body size, number of eggs, egg volume, and the presence of the parasite for each host. Moreover, settlement and growth of C. challengeri were followed in two fixed quadrats. Chthamalus challengeri brooded from February to June. The prevalence of B. japonica was high (often exceeded 10%) from April to July, and was rarely observed from September to next spring. The life cycle of the parasite matched well with that of the host. The parasite reduced the host’s brooding rate and brood size, to the extent that no hosts brooded in 2018.

Zonation of two barnacle species not determined by competition

Two barnacle species (Semibalanus cariosus and Chthamalus challengeri) were studied during two years at Hokkaido, northern Japan, to find the interspecies boundary and to determine whether interspecific competition (interference and pre-emption) is important in maintaining the zonation in our study system. Both barnacle species showed tide level dependent distribution patterns in the boundary zone. Semibalanus cariosus was dominant at lower levels; this pattern was determined by post-recruitment mortality. This mortality pattern seemed to be set by physical stress because recruitment density and survival rate were not correlated with the cover of other species, and mortality was higher in higher zones where physical stress is more severe. Chthamalus challengeri was dominant at higher levels; this pattern was determined by recruitment. The recruitment density and survival rate of this species were not affected by the covers of other species, thus, neither interference nor pre-emption significantly affected the distribution pattern. Interspecific competition appears to be less important in organizing barnacle communities in our study area than in previously studied areas, however, the recruitment process is of major importance.

The role of pre-recruitment processes in the maintenance of a barnacle (Chthamalus challengeri Hoek) patch on an intertidal pebble shore in Japan

To understand the role of pre-recruitment processes (supply of larvae and recruitment) in the maintenance of an intertidal barnacle (Chthamalus challengeri Hoek) patch, the availability of cyprid larvae and the recruitment on natural pebble substrata was monitored on the Magarisaki pebble shore (Amakusa, Kyushu, Japan) during 1995 and 1996. Also, a hypothesis that predation and/or bulldozing by mobile intertidal mollusks during the post-recruitment period could be an important factor in mortality of these barnacles was tested. The collapse of the adult population and the consequent disappearance of the patch were observed by the middle of 1995. The larval availability was low (<FONT FACE="Symbol">@</FONT> 6 cyprid larvae/100 l), as was the recruitment (<FONT FACE="Symbol">@</FONT> 30 recruits/25 cm²). The recruits experienced high mortality, preventing them becoming adults able to maintain the patch. In 1996, a similar pattern of availability of the cyprid larvae, and even lower recruitment occurring only at the upper intertidal level was observed. A mobile mollusks exclusion experiment failed to detect any significant differences among the treatments, supporting the null hypothesis that the observed pattern of distribution was not caused by predation by mobile mollusks. There is my suggestion that the low availability of larvae and the low level of recruitment caused the non-maintenance of the patch.

Temporal variations in community structure in and around intertidal barnacle (Chthamalus challengeri Hoek) patches on a plebby shore in Japan

The community structure in and around two barnacle (Chthamalus challengeri Hoek) patches (sites A and B) which extended from the middle to the upper intertidal zone on a pebbly shore in Magarisaki (Amakusa, Kyushu, Japan), was studied during summer and winter of 1995 and 1996. The results show a significant decrease in the proportion of substrate covered by barnacles from January 1995 to July 1996. The number of species, number of individuals, and biomass also decreased in the patch areas through time. There were significant differences between inside and outside the patches for percentage of substrate covered by barnacles, number of individuals, number of species, and biomass during the first year. Numbers of some gastropods were significantly higher in the barnacle patches, suggesting that the presence of barnacles create favorable microhabitat for the other taxa.