Sombat Poovachiranon

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.

Male courtship cycles in three species of tropical Ilyoplax crabs (Decapoda, Brachyura, Ocypodidae)

The courtship behaviour and cycles of male courtship activity and colouration of Ilyoplax orientalis, I. delsmani and I. gangetica were studied in the field in Malaysia and Thailand. Each species had a distinctive chela waving or beckoning display. Depending on species, the chelipeds, carapaces, or both of waving males blanched to white in contrast to the cryptic colour of nonwaving males and females. All three of these tropical Ilyoplax exhibited semilunar cycles in male waving activity at the colony level. It was confirmed for I. orientalis that individual males cycled each semilunar period between waving and non-waving phases and exhibited different behaviour toward females during these two behavioural phases.

Adaptations for feeding on rock surfaces and sandy sediment by the fiddler crabs (Brachyura: Ocypodidae) Uca tetragonon (Herbst, 1790) and Uca vocans (Linnaeus, 1758)

Two species of fiddler crab, Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758), which belong to the subgenus Gelasimus, dwell on rocky shores and muddy–sandy tidal flats, respectively, in Phuket Is., Thailand. We investigated their feeding ecology in relation to the morphology of their feeding organs: minor food-handling chelipeds and maxillipeds. U. tetragononfed chiefly on rocks covered by filamentous green algae. U. vocansfed on the emerged sand and in shallow water along the shoreline and in pools. While feeding, both crabs made sand pellets beneath their mouthparts and discarded them, indicating that they divided the matter scooped up with their minor chelipeds into edible and inedible fractions by using the maxillipeds in the water passing through their buccal cavity. The morphology of maxillipeds hardly differed between the two species, which means that both species are flotation-feeders. The morphology of their minor chelipeds, however, differed: the tips of the dactyl and pollex were flat in U. tetragononand pointed in U. vocans.When the minor cheliped was closed, U. tetragononhad a hemispherical space in the distal one-fourth of the gape, which was closed by the framing keratin layers and a few setae of the dactyl and pollex. On the other hand, U. vocanshad an ellipsoidal space in the distal half of the gape. We consider these morphological characters to be adaptations to the different feeding substrates for retaining more food-laden sediment. We discuss the role of the setae on the minor chelipeds on the basis of the morphological differences between populations of U. tetragononin Phuket Is. and East Africa where the crab inhabits muddy–sandy tidal flats.