The Effect of Muddy Bottom Sediment on the Abundance and Life Span of the Barnacle, Hesperibalanus hesperius, Epizoic on Scallop Shells

Barnacles are an important fouling component of molluscs of commercial value, and they may adversely affect their hosts. The abundance of living and dead individuals, survival of newly-settled young and the maximum life span of the barnacle, Hesperibalanus hesperius, encrusting the shells of the scallop, Patinopecten (Mizuhopecten) yessoensis, were compared for two sites differing in bottom sediment composition. It was found that muddy sediment (mud content > 25.5%) had an adverse effect on the survival of this barnacle. The valves of scallops collected from a sandy substratum had significantly more barnacles than scallops sampled from muddy sand. At the sandy site, the mean number of barnacles on the upper valves of 5-8-year-old scallops was 378.4 ± 9.6 individuals per valve, and on the lower valves, 92.3 ± 1.8 individuals per valve; of these, 38.5-48.3% were alive. At the muddy sand site, the mean number of barnacles on the upper valves of 5-8-year-old scallops was only 154.5 ± 4.5 individuals per valve, and on the lower valves, 31.7 ± 1.4 individuals per valve. However, living barnacles made up only 20.1-22.6% of the total number counted. On muddy sand, the number of barnacles per cm² of scallop valve increased with scallop age up to 3-5 years, after which it declined. However, on sand, the number of barnacles per cm² of scallop valve did not change with increase in host age from 5 to 8 years. The young barnacles settled in significantly greater numbers on the shells of scallops living on sand than on muddy sand. The mortality of barnacles during the first month after settlement on the upper scallop valves was about 45 and 80% on sand and muddy sand respectively. Old, large barnacles (with a shell base >10 mm), both living and dead, occurred more often on scallops living on the sandy substratum. The largest barnacles had a base length of 15-20 and 13-15 mm, at the sandy and muddy sand sites respectively. The possible reasons for these differences are discussed.

Keywords:

• Barnacle
• Benthic Ecology
• Biofouling
• Epibionts
• Scallop
• Sediments