Temporal patterns of abundance, biomass, and production of 3 populations of Caridina cantonensis (Atyidae) and 1 population of C. serrata were studied in 2 unshaded and 2 shaded Hong Kong streams. Monthly quantitative sampling was done in each of the 4 study sites over 2 y (April 2000–March 2002). Secondary production of C. cantonensis, estimated by the size-frequency method (PSF) and averaged over the study period, ranged from 1665 to 2274 mg ash-free dry mass (AFDM) m−2 y−1 according to site; PSF of C. serrata (810 mg AFDM m−2 y−1) was <½ that of C. cantonensis. Total shrimp production was greater at the 2 unshaded sites during both years. Interyear differences in PSF were not significant, but shrimp production was 10 to 83% higher during the dry season than the wet season, most notably in the 2 unshaded streams (≥40% higher). This seasonal difference probably was caused by mortality from spates associated with the summer monsoon. Production estimated by the instantaneous growth method showed the same trends as PSF, but yielded values 26 to 57% lower. Annual PSF/biomass ratios ranged from 2.02 to 3.89 and were correlated with cohort-specific growth rates of shrimp populations; neither parameter was directly related to the extent of shading. Instantaneous growth rates of Caridina spp. estimated from caged shrimps at each of the 4 study sites did not differ between years. Instantaneous growth rates in cages appeared correlated with cohort-specific growth rates of field populations, suggesting that the intra- and interspecific variations in PSF of Hong Kong atyids represent genuine ecological differences rather than methodological artifacts. Production of Caridina spp. was considerably higher than has been reported for other macroinvertebrate taxa in Hong Kong streams, constituting ˜10% of total macroinvertebrate production for these systems and demonstrating the importance of atyid shrimps in tropical stream food webs.
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