Diel vertical migration and feeding of three species of chaetognaths (Flaccisagitta enflata, Aidanosagitta delicata and Aidanosagitta neglecta) in two shallow, subtropical bays in Hong Kong

The diel behavior and feeding ecology of three coexisting species of chaetognaths in two shallow subtropical bays in the northeastern part of Hong Kong were studied in summer 2005 and winter 20052006. Average densities of adult Flaccisagitta enflata, Aidanosagitta delicata and Aidanosagitta neglecta ranged from 21 to 48 ind. m(3) in the semi-enclosed Tolo Harbour, but densities of the two Aidanosagitta species were low in Mirs Bay, which is deeper and opens into the South China Sea. Adult F. enflata, the largest of the three species, exhibited the most pronounced diel vertical migration (DVM) and diel feeding rhythm. The smaller juvenile F. enflata and adult A. delicata did not exhibit DVM. Although copepods were the most abundant component of the mesozooplankton, they were not preferred prey of chaetognaths. Predation impacts on copepods were generally 0.3 of the standing stock. Larvaceans, on the other hand, were highly preferred, with predation impact as high as 30. As prey abundances in Tolo Harbour could be 9 10(4) ind. m(3), there was no evidence of resource partitioning behavior by the coexisting chaetognaths.