icolls - Sustainable Tourism CRC

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS
For A. australis individuals there was general agreement between the contributions of prey items to
individual diets (Figure 6). However, mixing model analyses indicated that a greater contribution from teleost
fish was to be expected on the basis of muscle carbon and nitrogen signatures (Figure 6). Furthermore,
difficulties associated with identification of prey items in some guts (high miscellaneous contribution in Figure
6) makes comparisons between these two methods difficult.
Figure 6: Comparison of gut contents and stable isotope analyses of percent contribution of prey types to
the diet of A. australis individuals in Belongil Creek
Given that the diet of M. cephalus is generally dominated by miscellaneous detritus and particulate matter
(Table 9 and 10) and that similar catch sizes were recorded in Belongil and Tallows Creeks (Table 8), we used
mixing model reconstructions of dietary compositions from primary carbon sources to compare the basis of M.
cephalus nutrition in the two sites. Whilst epilithon contributed almost 100% of the carbon and nitrogen in M.
cephalus muscles in Belongil Creek, equivalent contributions were made from epilithon, seston and riparian
vegetation in Tallows Creek (Figure 7).
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100%
80%
60%
40%
20%
0%
100%
80%
60%
40%
20%
0%
Gut Contents Mixing Model
Tallows Belongil
Gastropods
Polychaetes
Decapods
Figure 7: Mixing model analyses of sources of carbon contributing to M. cephalus diets from individuals
caught in Tallows (n=12) and Belongil (n=13) Creeks
Stable isotope analyses revealed that S. ciliata individuals fed on a broader range of prey taxa than was
revealed on the basis of gut contents analyses (Figure 8). While the guts of many individuals were full of
polychaete worms (Table 9 and 10), isotope data indicates that these prey items had contributed only a small
proportion of the dietary carbon and nitrogen in their muscle tissues. Other teleost fish, decapod crustaceans and
gastropod molluscs also contributed to S. ciliata diets despite the low abundance or complete absence from the
guts of individuals in both sites.
Fish
Epilithon
Seston
Miscellaneous
Riparian Vegetation