MEPS 321:203-214 (2006)  -  doi:10.3354/meps321203

Distance effects on patterns and processes of dispersal in an octocoral-associated amphipod

Naoki H. Kumagai*

Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka 415-0025, Japan
Present address: Graduate School of Science and Technology, Chiba University, 1–33 Inage, Chiba 263–8522, Japan

ABSTRACT: Similar to pelagic larval dispersal, it has been suggested that dispersal of post-larval benthic organisms and species with direct development plays an important role in population persistence. However, effective dispersal distances required for the maintenance of local populations have been poorly characterized. This study elucidated distance effects on patterns and processes in dispersal of the amphipod Incisocalliope symbioticus, which is associated exclusively with the gorgonian octocoral Melithaea flabellifera. Dispersal patterns over an annual cycle were examined by the placement of defaunated gorgonians at 3 distance levels (<0.2, 8, 70 m) for 1 wk. With an increase in distance from the source population, the dispersal rate decreased; conversely, the proportion of females and large individuals increased. This result suggested that colonizers that dispersed over long distances had the potential for rapid establishment of breeding aggregations, and therefore were responsible for the maintenance of local populations. Furthermore, the short-distance dispersal within a local population was dependent on the density of the resident population, whereas middle- and long-distance dispersal resulted from density-independent passive transport, driven by typhoon and storm events. Results of direct observations on the movements of live and, as a control, dead amphipods toward a gorgonian patch in the field showed that the amphipods had sufficient swimming ability (3.4 m min–1) for short-distance dispersal, and actively selected to move toward the patch. These results indicated that the combination of passive transport and the active selection enables the amphipod to migrate over long distances among local populations, even though the habitat of the amphipod only occurs sporadically.

KEY WORDS: Population persistence · Direct development · Host specialization · Storm · Gorgonian

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