Effects of temperature, salinity and food on the life histories of Balanus amphitrite amphitrite Darwin and Hydroides elegans (Haswell)

The barnacle Balanus amphitrite amphitrite and the polychaete Hydroides elegans, both dominant species in Hong Kong's fouling communities, exhibit dramatically different seasonal recruitment patterns. Previous field studies have led to some speculations on the relationship between environmental factors and recruitment seasonalities of these two invertebrates. In this study, I present a quantitative assessment of the effects of temperature, salinity, and food on the maturation, fecundity, larval survival, larval growth, and settlement of B. a. amphitrite and H. elegans. The results show that these two species, which are both r-selected species, differ dramatically in their responses to a similar set of manipulated environmental conditions. Although the adults of both species are quite resistant to short-term starvation, the larvae of B. a. amphitrite are more sensitive to food-deprivation than those of H. elegans. High temperature promotes survival, growth and reproduction in both species, but the reproduction and larval development of B. a. amphitrite are more vulnerable to a decline in temperature than those of H. elegans. All stages of B. a. amphitrite have a similarly high capacity of hypo-osmoregulation and this capacity was altered very little by large fluctuations in salinities ≥ 15‰. The tolerance of H. elegans differs with developmental stage: adults and older juveniles survived well at ≥ 20‰ whereas blastulae could survive only at ≥ 30‰. These results indicate that the sensitivity of these two species to fluctuations of temperature, salinity and food could account for the dominance of H. elegans in the winter and spring and that of B. a. amphitrite in the summer.;In this study I have also examined the plasticity of some developmental traits and acclimation in B. a. amphitrite. The data shows that food concentration, temporary starvation, culture method or larval source do not affect the larval size or settlement ability of B. a. amphitrite cyprid. However, hypo-osmotic stress experienced by one developmental stage has detrimental effects on the survival or development time of the next stage. These results should be taken into account in bioassays involving the use of barnacle larvae and in explaining the growth variability among different batches of juveniles.