THE ABUNDANCE AND GROWTH OF AVICENNIA-MARINA AND RHIZOPHORA-STYLOSA IN THE LOW SHORE ZONE OF DARWIN HARBOR, NORTHERN-TERRITORY

The growth and distribution of the two mangrove seedling species, Avic ennia marina (Forsk.) Vierh, and Rhizophora stylosa Griff., were studi ed in the low-shore zone at three locations along two estuaries of Dar win Harbour to determine how growth varied along the estuary and withi n the habitats of the low shore zone. The low shore environment was he terogenous for factors such as salinity and light, with substantial va riation within and between locations. Seedlings of Avicennia were in h igher densities in light gaps than in the adjacent forest, and density in both habitats decreased towards the mouth of the estuary. Growth o f Avicennia seedlings, as measured through in situ growth trials and p lant harvests, increased towards the mouth of the estuary. Results for Rhizophora seedlings were more complex although some similar trends w ere evident. This may have been due to the greater early survival of R hizophora seedlings compared to Avicennia seedlings. The importance of propagule origin was investigated, for Rhizophora, by transplanting p ropagules between locations along one estuary. Increased seedling surv ival was observed at the propagule source site; however, this effect w as subtle and probably not the most important factor affecting seedlin g survival at a site.