Some observations on food and feeding of the supralittoral beach-hopperOrchestia gammarellus(Pallas) (Crustacea: Amphipoda)

Abstract

Abstract The composition of faeces from Orchestia gammarellus collected from different supralittoral biotopes was found to vary according to position on the shore. Consumption of different materials was to some extent a function of availability. Material of plant origin dominated: few animal fragments were found in the faeces. In short-term habitat selection experiments O. gammarellus chose to congregate amongst wetted straw rather than chopped kelp (perhaps reflecting availability of void space). Over the longer term, in raw straw/alga mixtures, O. gammarellus preferentially consumed algal material. The size of angiosperm vascular (tracheid) elements consumed by O. gammarellus gave insight into food particle handling by the amphipod. The maximum length of tracheid elements approximated to oesophagus length suggesting that more rigid particles are pushed or sucked through the mouth lengthways until the proximal end reaches the opening of the stomach whereupon the distal end is bitten off. Given a choice between hard and soft food items, Orchestia gammarellus habitually chose to consume softer items. Certain red algae and Ulva may be unpalatable. Gut residence time at 10 °C is ∼ 10-22 h. Food consumption was markedly reduced in continuously-lit conditions but continued at a high level under aerated water. Acidification of seawater to pH values <6.8 inhibited feeding. Presented with agar made up with different salt contents O. gammarellus ate more of (and preferred) the more saline food. Alkali treated, macerated straw was an acceptable food for all size-classes. Orchestia gammarellus exhibited little reaction to amino acid tainted filter paper (present at 10-2 M), except for glycine.