SYSTEMATIC AND BIOLOGICAL STUDIES OF THE BARNACLES (CIRRIPEDIA: THORACICA) OF SINGAPORE WITH SPECIAL REFERENCE TO THE BALANUS AMPHITRITE COMPLEX

Abstract

This dissertation is a study of barnacles (cirripedia: Acrothoracica) of Singapore. Its equatorial situation, peculiar tidal regime, relative low salinities, and variety of marine habitats give special interest to studies on Singapore's marine fauna. The barnacle fauna is fairly rich, including some twenty species, one of which is described (in the appendix) as new. A key to the species is provided. Three members of Balanus amphitrite complex form prominent barnacle populations along the coast. There are reasons to suggest that these are good species. They are B. amphitrite, B. variegatus, and B. cirratus. These species of B. amphitrite complex have specific habitat preferences, in addition to certain anatomical differences. Studies have been made on breeding, growth and settlement of members of the B. amphitrite complex. Attempts were made to find out the age of maturity and periods of breeding intensity of B. amphitrite and B. cirratus. Protogyny in these species is not obvious, although there is an indication of the slightly earlier development of female gonad. The species reach maturity at an extremely early age. The cycle of gametogenesis is very rapid, while breeding seems to occur throughout the year, with certain breeding peaks, which in Tg. Gul give some suggestion of lunar periodicity. No obvious connection was observed with monsoon periods. Considerations are made for the appropriate methods for measuring growth. Measurements of growth are made difficult by the fact that a barnacle changes the shape of its shell when it grows in overcrowded conditions or on an uneven surface. Results of observations suggest that a sigmoid growth curve is generally followed, but the specific growth rates vary at different tide levels. Settlement is continuous throughout the year, but the density of settlement fluctuates unevenly, with occasional peaks of exceptionally heavy spats. Reasons for these fluctuations are not well understood, but settlement at high water level may depend on coincidence with favourable high tides.