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SEASONAL ZONATION PATTERNS OF BENTHIC AMPHIPODS IN A SANDY SHORE SURF ZONE OF KOREA

Abstract Seasonal zonation patterns of amphipods with various life styles and feeding habits were analyzed in a temperate sandy shore surf zone using a sledge net. The range in distribution of the burrowers Synchelidium lenorostralum and Urothoe convexa did not change seasonally: the former was usually found in the sandy shore from 1.0 to 3.0 meters below mean sea level (MSL) and the latter from 3.0 to 0 m below MSL. On the other hand, the distribution ranges of the nestlers Pontogeneia rostrata and Allorchestes angusta and the epifaunal tube-dweller Jassa slatteryi were restricted from 1.0 m above to 2.0 m below MSL, showing seasonal movement from below MSL in winter to above MSL in summer. Distribution centers of P. rostrata and A. angusta were located at 1.0 m below MSL and at 1.0 m above MSL in summer, respectively. This implies that habitat segregation occurred in summer. Gut contents analysis revealed that S. lenorostralum fed mainly on harpacticoid copepods, while P. rostrata, A. angusta, and U. convexa fed on phytoplankton and detritus. It is likely, therefore, that in summer, the segregation between P. rostrata and A. angusta may reduce competition for food. We suggest that feeding habits and life styles of amphipods in the sandy shore surf zone may be important factors controlling seasonal zonation patterns.