Food preference studies and ingestion rate measurements of the mangrove amphipod Parhyale hawaiensis (Dana)

Abstract

Large populations, up to 7000 individuals·m −2, of the amphipod Parhyale hawaienis (Dana), not previously reported for Australia, were found in a mangrove forest near Cape Ferguson, northern Australia. The amphipod inhabits accumulations of decomposing Rhizophora stylosa Griff. detritus in the upper littoral zone. Laboratory studies, using measurements of faecal production as an index of feeding rate, showed that the amphipod could consume large quantities of decomposing R. stylosa leaves, with maximum faecal production in the order of 1700 mg·g amphipod −1·day −1 (dry weights), depending on favourable salinity and food source conditions. Feeding rates were not significantly different over the salinity range 15–35%., although significant decreases were noted at further extremes i.e. 10 and 40%.. Short-term (24 h) and long-term (8 wk) food preference and survival studies showed a highly significant increase in food preference with increasing degrees of leaf decomposition. Proximate chemical and physical analyses of different stages of decomposed leaf material showed strong, significant correlations between feeding (defaecation) rate and leaf nitrogen, starch (positive correlations), tannin, crude fibre and toughness (negative correlations). An estimated maximum rate of faecal production in the field of up to 10 g dry matter·m −2·day −1 indicates that this amphipod may be an important component of the mangrove detritus-based food chain in the area studied.