The feeding biology of Mictyris longicarpus Latreille, 1806 (Decapoda: Mictyridae) was examined from laboratory studies and field studies in Moreton Bay, Queensland. M. longicarpus feeds on organic detritus, sorted from the substratum by flotation with water within the mouthparts.
During surface activities, M. longicarpus collects interstitial and free standing water via setae on the posterior border of the carapace and the proximal edge of the first abdominal segment. Water is lifted to the bases of the scaphognates by capillary action, travelling from the posterior setae into a posterior chamber under the epibranchiaL membranes. The scaphognathites provide the necessary force to pump water into the buccal cavity. Water which flows out of the buccal cavity is collected between the abdomen and the cephalothorax by setae fringing the abdomen, and returned to the posterior chamber by the ventrolateral canals.
The frequency of water uptake behaviour pattern was significantly increased while crabs were feeding, and was inversely related to the amount of moisture in the substratum on which the crabs were feeding.
Measurements of organic carbon, organic nitrogen, algal and bacterial biomass were made from the substratum and the proventricular contents. The amount of material ingested per gram sorted was estimated to be 0.5 mg. The material ingested had a high organic content (between 64 and 80% organic matter) with evidence that bacteria were concentrated during sorting. Bacteria constituted 35% of the organic carbon in the proventriculus. Assimilation effeciencies of organic material in the proventriculus were 86% and 89%, for carbon and nitrogen respectively.
During feeding, the rates of scooping the substratum and production of feeding pellets were significantly higher in run-off channels than on moist and dry substrata. The weight of substratum sorted per minute was 108 mg; giving an estimated ingestion rate of 0.54 mg/min. Ingestion rate was also estimated based on consecutive weights of material in the proventriculus. This method provided estimates of ingestion rate for crab sizes between 15 and 19 mm carapace length. The relationship between ingestion rate (mg/min) and carapace length (mm) was Ln(ingestion rate) = 4.63 Ln(carapace length) – 13.37 The results of a laboratory experiment agree with the above estimates of ingestion rates.