Importance of freshwater flow in terrestrial-aquatic energetic connectivity in intermittently connected estuaries of tropical Australia

delta C-13 was used to identify seasonal variations in the importance of autochthonous and allochthonous sources of productivity for fish communities in intermittently connected estuarine areas of Australia's dry tropics. A total of 224 fish from 38 species were collected from six intermittently connected estuarine pools, three in central Queensland (two dominated by C-3 forest and one by C-4 pasture) and three in north Queensland (one dominated by C-3 and two by C-4 vegetation). Samples were collected before and after the wet season. Fish collected in the two forested areas in central Queensland had the lowest delta C-13, suggesting a greater incorporation of C-3 terrestrial material. A seasonal variation in delta C-13 was also detected for these areas, with mean delta C-13 varying from -20 to -23aEuro degrees from the pre- to the post-wet season, indicating a greater incorporation of terrestrial carbon after the wet season. Negative seasonal shifts in fish delta C-13 were also present at the pasture site, suggesting a greater dependence on carbon of riparian vegetation (C-3 Juncus sp.) in the post-wet season. In north Queensland, terrestrial carbon seemed to be incorporated by fish in the two C-4 areas, as delta C-13 of most species shifted towards slightly heavier values in the post-wet season. A two-source, one-isotope mixing model also indicated a greater incorporation of carbon of terrestrial origin in the post-wet season. However, no seasonal differences in delta C-13 were detected for fish from the forested area of north Queensland. Overall, hydrologic connectivity seemed to be a key factor in regulating the ultimate sources of carbon in these areas. It is therefore important to preserve the surrounding habitats and to maintain the hydrologic regimes as close to natural conditions as possible, for the conservation of the ecological functioning of these areas.