Inter- and intraspecific differences in the life history and growth of Caridina spp. (Decapoda: Atyidae) in Hong Kong streams

Abstract

1. The life-history pattern of three populations of Caridina cantonensis (Atyidae) and one population of Caridina serrata were studied in four Hong Kong streams: Pak Ngau Shek (PNS), Kap Man Hang (KMH), Pak Tam Chung (PTC), and Lung Fu Shan (LFS). Caridina cantonensis occurred at PNS, KMH and PTC while C. serrata was present at LFS only. Monthly quantitative sampling was carried out at each study site over 2 years to investigate life-history patterns and cohort-specific growth rates. 2. Breeding by both species was mainly restricted to the wet season, and there was an increase in the incidence of ovigerous females as water temperatures rose at the start of the summer monsoon. The number of cohorts and the frequency of recruitment of C. cantonensis (one to three times each year) were highly site-specific, but consistent between years. 3. Shrimp growth was size-dependent, and decreased with increasing body size. Caridina cantonensis at PTC had the highest cohort-specific growth rates (0.05-0.14 mg ash-free dry weight (AFDW) mg-1 day-1), followed by C. serrata at LFS (6% lower), and C. cantonensis at KMH and PNS (16-39% lower). Shrimp life spans exceeded 1 year (17-22 months), depending on site and species. 4. Sexual maturity occurred at an earlier age and at a smaller size in populations with higher growth rates. Shrimps at PTC and LFS matured at approximately 4 months old; this was 3 months earlier than at KMH and 5 months earlier than at PNS. Females of C. cantonensis at PTC and C. serrata at LFS may have bred twice during each breeding season, while females in the other two populations bred once only. The number of cohorts produced by each population in each year did not vary between the years of the study. Most sexually mature individuals only survived long enough (for 10-12 months after maturation) to breed during one season. 5. The mean brood size of C. cantonensis varied among streams and was 25-28% larger at PNS and KMH than at PTC. Egg size did not differ among populations. Larger brood sizes at PNS and KMH may have been a consequence of increased availability of algal food in these unshaded stream sites. Caridina serrata had similar egg and brood sizes to C. cantonensis, but females were smaller and reproductive investment was higher. Thus, the degree of intraspecific variation in atyid breeding in Hong Kong was at least equal to, if not greater than, the extent of interspecific variation. Interspecific differences in life history may reflect the frequency of droughts and spate intensity experienced by C. serrata at LFS. © 2005 Blackwell Publishing Ltd.