MEPS 177:93-102 (1999)  -  doi:10.3354/meps177093

Differential recruitment of annelids onto tidal elevations in an estuarine mud flat

Hwey-Lian Hsieh1,*, Chi-Feng Hsu1,2

1Institute of Zoology, Academia Sinica, Taipei, Taiwan 115, Republic of China
2Institute of Fisheries Science, National Taiwan University, Taipei, Taiwan 106, Republic of China

ABSTRACT: The recruitment of an annelid community was examined on 2 tidal elevations in 2 kinds of sediments along an inclined intertidal mud flat in an estuary in northern Taiwan. Recruitment onto defaunated and ambient intact sediments (control) in both low and high tidal zones was followed weekly from 3 April to 1 May 1996. The overall density of recruits in the defaunated sediments reached the level of the control sediments within 3 wk in the low tidal zone, whereas in the high tidal zone the density of recruits did not reach the control level during the study period. Two polychaete species and 1 oligochaete species were the major recruits, and each exhibited a different recruitment mode and rate. The spionid Prionospio japonica and the oligochaete Doliodrilus tener were among the most rapid recruits. P. japonica simultaneously exhibited 2 recruitment modes, larval settlement and postlarval transportation, and its recruit density in the defaunated sediments in the low tidal zone reached the level of the control within 1 wk. D. tener recruited predominately by means of juvenile migration. In general, recruitment by settling larvae occurred at discrete intervals, whereas that by postlarvae or juveniles appeared to be continuous. The densities of P. japonica and of D. tener exhibited a zonation pattern wherein density increased along a down-shore gradient. The sedimentary characteristics also exhibited a similar zonation pattern, wherein the sediment particles became smaller and silt/clay content increased in the low tidal zone. This coupled phenomenon suggests that tidal action has a strong influence on the recruitment of P. japonica and D. tener. These recruits are passively entrapped in the low tidal zone due to the depositional conditions created by slow flows. However, the tidal zonation of the capitellid Capitella sp. showed an opposite trend, with greater recruitment in the high tidal zone, indicating that the recruitment of Capitella sp. possessed an active component. D. tener recruited mostly into the low tidal zone, but a small, significant proportion of the recruitment occurred in the high tidal zone. Capitella sp. and D. tener are subsurface burrowers, and thus, to some extent, their recruitment is less controlled by tidal action. Overall, the recruitment of this annelid community is influenced by both physical and biological controls.

KEY WORDS: Annelid recruitment · Tidal elevation · Defaunation · Estuary

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