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Diversity At A Glance (pdf)

This column aims to introduce interesting species of Hong Kong flora and fauna that might be encountered during fieldwork. Distinctive physical characteristics and some interesting ecological facts are included for each example.

Editors : Jacqueline Weir (jesweir@hkusua.hku.hk) and
David Poon (dynpoon@graduate.hku.hk)

Atyid shrimps in Hong Kong streams

by Rita S.W. Yam

Atyid shrimps, notably the genus Caridina, are widespread in tropical and subtropical streams. They can act as filter-feeders, collector-gatherers and omnivorous scavengers (Hart, 1981; Pringle et al., 1993) and, because of their biomass and abundance, may play a key role in the organization of lotic communities.

Atyid shrimps have a long rostrum that usually extends beyond the eyes. They are sexually dimorphic after maturation; ovigerous females have large eggs, and the larvae undergo direct development (Dudgeon, 1987; Cai & Ng, 1999). Four species of Caridina shrimps have so far been found in Hong Kong. Caridina cantonensis (Fig. 3), C. apodosis and one previously unrecorded species C. trifasciata (Yam & Cai, in press) occur in streams in the mainland New Territories, while C. serrata is apparently endemic to Hong Kong Island (Cai & Ng, 1999; Yam, unpublished data).

These tiny little shrimps range between 0.9 9.8 mm (C. cantonensis), and 1.2 7.4 mm (C. serrata) in carapace length. Caridina usually inhabit trailing vegetation at stream banks. They are also found associated with leaf packs accumulated in stream pools. Hong Kong atyids generally have an annual life cycle and breed when water temperatures exceed 20oC (i.e. spring and summer) (Dudgeon, 1985). Wet season spates are common in Hong Kong streams, direct development of the Caridina larvae, therefore, reduces spate-induced mortality because the juveniles, as a small replica of the adults, are able to grasp trailing vegetation and roots thereby avoiding being swept away during spates.

Studies on the ecology of atyids shrimps have, however, received scant attention. As a result, it is difficult to make any generalizations about the possible ecological roles of atyids, especially in southeast Asia. My research begins at studying the population dynamics of C. cantonensis and C. serrata in Hong Kong streams. My study is further directed to investigate the role of atyid shrimps in the stream food webs using stable isotope analysis. As C. cantonensis and C. serrata are truly freshwater species, gene flow among populations may be highly limited as a result of their intolerance to high salinity and incapability of terrestrial dispersal. Therefore, my study also focuses on the genetic differentiation of C. cantonensis and C. serrata. The results could have conservation implications for C. serrata, which is apparently an island endemic.

Bibliography

Cai, Y. & Ng, N.K. (1999). A revision of the Caridina serrata species group, with descriptions of five new species (Crustacea: Decapoda: Caridea: Atyidae). Journal of Natural History 33: 1606-1638.

Dudgeon, D. (1985). The population dynamics of some freshwater carideans (Crustacea: Decapoda) in Hong Kong, with special reference to Neocaridina serrata (Atyidae). Hydrobiologia 120: 141-149.

Dudgeon, D. (1987). The larval development of Neocaridina serrata (Stimpson) (Crustacea: Decapoda: Caridea: Atyidae). Archiv für Hydrobiologie 110: 339-355.

Hart, R.C. (1981). Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya. Freshwater Biology 11: 531-547.

Pringle, C.M., Blake, G.A., Covich, A.P., Buzby, K.M., Finley, A. (1993). Effects of omnivorous shrimp in a montane tropical stream: sediment removal, disturbance of sessile invertebrates and enhancement of understory algal biomass. Oecologia 93: 1-11.

Yam, R.S.W. & Cai, Y. (in press). Caridina trifasciata, a new species of freshwater shrimp (Decapoda: Atyidae) From Hong Kong. The Raffles Bullettin of Zoology.

Fig.3. "Caridina cantonensis"

P.15-16
 
   

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