Effect of epibiosis on the fitness of the sandy shore snail<Emphasis Type="Italic"> Batillaria zonalis</Emphasis> in Hong Kong

Batillaria zonalis is a common snail on Hong Kong sandy shores, occupying the low-mid shore. Shells of B. zonalis (basibiont) are often fouled with the rock oyster Saccostrea cucullata and the barnacle Balanus reticulatus (epibiont). This epibiotic interaction has a negative impact on the fitness of B. zonalis in terms of impairing fecundity, mobility and metabolism of fouled individuals. During the reproductive season, fouled snails had lower Gonadosomatic Index and fewer egg-bearing individuals than non-fouled snails. Fouled snails crawled in a more tortuous pathway and with lower speed when compared with non-fouled snails. Reduction in oxygen consumption and metabolic rate in fouled snails further suggested the restriction in mobility of B. zonalis by the epibionts. Glycogen content in the foot muscle tissues and hepatopancreas of fouled and non-fouled snails was, however, similar, revealing epibiosis does not influence the energy storage of B. zonalis. Mortality of fouled and non-fouled snails was similar under laboratory conditions, suggesting epibiosis does not influence the survivorship of B. zonalis in Hong Kong. Impairment in the fitness of fouled B. zonalis indicates that epibiosis can influence the population dynamics of B. zonalis in Hong Kong.Communicated by T. Ikeda, Hakodate