Abstract

The foregut contents of marron Cherax tenuimanus from a natural reservoir were predominantly composed (on average 83.77 ± 6.41%) of organic matter. This percentage did not vary with sex, season or age/size of the marron. Approximately 61% of the foregut contents by weight was composed of fine particulate organic matter (FPOM) smaller than 40 µm. Approximately 21% and 18% of the weight of the foregut contents comprised material between 40 - 500 µm in size and larger than 500 µm respectively. The distribution of the weights of the size fractions was similar between sexes and seasons. Marron >48 mm OCL tended to consume less FPOM and more coarse material than did marron of <28 mm OCL. The volumes of the dietary components in all three size classes of marron ranged between: 40.2 - 47.8% for FPOM; 22.5 - 32.2% for wood fragments; 2.0 - 6.3% for plant fibre; 0.5 - 7.0% for leaf fragments; 2.0 - 7.5% for terrestrial insects; 2.2 - 5.5% for roots; 3.5 - 8.2% for indigestible animal remains; 0.7 - 8.5% for aquatic insects; 1.4 - 2.2% for flowers and seeds; and O - 1.6% for sand. The visually determined volumes of the FPOM were underestimated by 15-20% compared to the more accurate sieving and weighing techniques. The percentage occurrence of each of the categories of material ingested followed a similar pattern to that of volumes ingested. Diatom frustule densities averaged 56.5 ± 13.7 ml^-1 of the gut contents of juveniles and adults. Food resources appear to be predominantly associated with the FPOM fraction of the detrital food chain. The coarse component comprised coarse refractory vegetable matter of terrestrial origin, which was clearly discernible in the faeces and therefore is considered to be of minimal nutrient value. The quantity of animal material ingested, terrestrial and aquatic insects, decreased with the size of the marron sampled and considering that it includes indigestible exoskeletons, appears to be too small to be a predominant food source. Diatoms are also considered to be of minor quantitative importance in the diet of marron. Differences in dietary constitution between sexes and seasons were minimal. Marron are most accurately describe as predominantly microphagic detritivores with the capacity to be opportunistic omnivores.

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