AbstractThis research has filled some of the gaps in knowledge of the function of grapsid crabs in mangrove forests by identifying some of the important factors affecting the consumption of mangrove litter. Grapsid numbers were related to mangrove litter consumption, in space and time. Feeding preferences, their significance for the consumption of mangrove, material and the survival of seedlings were also identified.
The thesis objectives were accomplished by sampling crab numbers and litter consumption in several assemblages, up-stream and down-stream of two areas in Darwin Harbour for a two-year period. Feeding preferences, of the most abundant grapsid crabs in the harbour, were studied in the laboratory.
The results from this study indicated that Sesarma spp., N. meinerti, Episesarnia sp. nov were the most abundant crab species, followed by C. merguiensis, I. paludicola, S. borneensis, M. latifrons, and Sarmatium spp.. Mangrove assemblage was the most important spatial factor affecting the distribution and abundance of grapsid crabs. Sesarma was most abundant in mid and low intertidal assemblages. C. merguiensis, I. paludicola, M. latifrons, and Sarmatium spp. were almost exclusively found in low intertidal assemblages. N. meinerti and Episesarma .sp. nov were largely limited tohigh intertidal assemblages. S. borneensis was the only species that was found dispersed in similar, numbers among the different assemblages. In many cases, crab species occurrence and abundance were specific to certain, assemblages, areas, mid-intertidal assemblage, where Sesarma spp. was dominant, C. tagal was the only option. C. tagal was consumed much less than mangrove litter in other assemblages. Sesarma, in the mid-intertidal, may turn to particulate organic matter to fill its nutritional needs.
Mangrove litter consumption rates increased from the dry season to the wet season. Mangrove productivity also increased from the dry season to the whet season. Interestingly, litter consumption rates were not related to litter fall rates. An explanation for the lack of relationship between litter fall rates and litter consumption rates may be associated with the nature of the experiment.
The structure of Darwin Harbour mangrove forests did not appear to be significantly effected by grapsid crabs. It has been suggested that in some mangrove forests, grapsid crabs may affect the structure of the forest by consuming propagules that would otherwise establish and proliferate. High consumption of A. marina and C. tagal propagules occurred in assemblages where both of these species are high in numbers.
|Date of Award||2004|
|Supervisor||Keith Mcguinness (Supervisor)|