Mangrove litter production, Darwin Harbour, Northern Territory

  • Kristin Metcalfe

    Student thesis: Coursework Masters - CDU


    The mangroves of Darwin Harbour represent one of the most extensive and diverse assemblages on Australia’s northern coastline. The Harbour’s large tidal range (7.8 m), climatic and environmental characteristics produce a distinctive pattern of mangrove zonation, recently stratified as 8 major communities or zones.

    Measurements of mangrove litter production are reliable indicators of net primary productivity and are highly relevant given the ecological role of mangroves in supporting vast detrital-based food webs. Litter fall within the 8 major mangrove zones of Darwin Harbour, measured between March 1997 and December 1998 was found to differ significantly between zones, but shows little spatial variation across the 3 arms of the harbour.

    The highest rates of between 2.69 to 3.48 g m-2 day-1 (dry weight) were found in the most seaward zones dominated by Sonneratia alba (Zone 8) and Rhizophora stylosa (Zone 1). A maximum rate of litter fall of > 1,800 g m-2 year -1 was recorded for the Sonneratia zone in East Arm. The seaward zones occur between -1.5 and 2.5 m AHD but occupy only 8% of the total mangrove area. In contrast, Zone 4 is the most extensive community, comprising Ceriops-dominated forests (at between 2 and 3.5 m AHD) occupy 40% of the total mangrove but have the lowest productivity (1.23 g m-2 day-1; 394 g m-2 year -1).

    Production of litter shows significant temporal variation (p=0.01), both between months and interannually. This variation appears to reflect strong spatial variation and marked seasonal differences in soil and environmental characteristics. Indeed, significant negative correlations were found between annual productivity and mean dry season soil conductivity, pH and moisture content. Significant relationships were also found between productivity and tree height and % canopy cover. Ranked estimates of flowers and fruit indicated a general peak in flowering during the late dry and early wet season (October to December). Peak fruit/propagule production for most species occurs during the wet season (November to January).

    Topographic elevation data indicates that the height of the major zones is consistent throughout the harbour. This research indicates that spatial patterning and productivity of mangrove zones in Darwin Harbour is predictable, and reflects the importance of those environmental factors governed by the frequency and duration of tidal inundation to the structure and function of these systems.

    Note: Please note that the author has made all reasonable efforts to contact the copyright owner for permission of "Figure 1 : Map of Darwin Harbour mangrove communities showing zonation and location of 8 transects established for leaf litter fall studies -- page 17" but to no avail.
    Date of AwardJan 1999
    Original languageEnglish
    SupervisorKeith Mcguinness (Supervisor)

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