Larval biology and ecology of a non-indigenous species, the slipper limpet crepidula onyx
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AbstractThe slipper limpet Crepidula onyx is a non-indigenous species (NIS) in Hong Kong waters introduced in 1970s from the United States. This species has established a small dense population in Victoria Harbour but not in western and eastern waters of Hong Kong. In this study I first examined the effects of temperature, salinity and food on the larval survival, growth and settlement as well as juvenile development of C. onyx. I found that short-term food deprivation, especially in the first two days of larval development, has detrimental effects on larval development; and that both low salinity and temperature reduced survival and growth rate of larvae and juveniles, and prolonged the pre-competent period. These results indicate that confined geographic distribution pattern of C. onyx is closely linked to larval tolerance to salinity changes and larval food supplies in Hong Kong waters. To have a better understanding of aggregated distribution pattern of this species, the larval settlement of C. onyx in response to multiple natural cues derived from conspecifics, natural biofilms and sympatrics was investigated in this study. The results showed that cues derived from adult Crepidula onyx or sympatric mussel, Perna viridis, were waterborne. However, the cues from the biofilm were surface- associated and dependent on the components of biofilms. Both waterborne conspecific cues (or sympatric mussel cues) and surface associated biofilm cues may act synergistically, leading to the aggregated distribution of adult C. onyx or associative attachment of C. onyx to mussel in nature. Furthermore, larval settlement in response to biofilms of different ages was affected by both bacterial abundance and the differences of bacterial community structure while the response to bacterial film was strain-specific, indicating that shift in dominancy of certain bacterial strains in biofilm over time is crucial for the induction of larval settlement and metamorphosis.