Response to suction dynamics on intertidal distribution of <i>Haustorioides</i> amphipod species on East Asian sandy beaches during diurnal tidal changes

Abstract

Intertidal distribution of Haustorioides amphipods were studied in relation to the tidal fluctuation at four sandy beaches in Japan and Korea, to understand their behavioral responses to environment during tidal fluctuations. Presence or absence of Haustorioides individuals (including four species: H. japonicus, H. koreanus, H. munsterhjelmi, and H. nesogenes) were generally recorded at 2 m intervals from the drift line to the swash zone at various tidal conditions including high tides and low tides. Generalized linear mixed models demonstrated that the occurrence of Haustorioides amphipods at the sampling points were best described by a model with suction (the tension of moisture in the sediment) as an explanatory variable. Other environmental variables at the sampling points (slope angle, distance from the shoreline at the sampling time, and height from the sea level at the sampling time) were relatively poor predictors. The model showed that the probability occurrence of the amphipods was highest at the suction value of 0.76 kPa. Thus, the tidal migration behavior of these Haustorioides amphipods can be explained by suction dynamics rather than the swash conditions. This response was common to all four species and appears to be consistent over various tidal conditions.