DISPERSAL OF GRAY MANGROVE (AVICENNIA-MARINA) PROPAGULES IN SOUTHEASTERN AUSTRALIA

Dispersal in Avicennia marina was related to attributes of the propagu les and their response to environmental conditions. Viability of propa gules and periods of their dispersal were measured in field experiment s. Propagules extended their hypocotyl and developed root primordia wi thin a few weeks, hence the phase of obligate dispersal is about 1 wee k. However, propagules remain viable, either exposed by tides or total ly submerged, for up to 5 months during enforced dispersal. The fates of propagules were followed in two types of tidal creek over three tid al cycles. Newly released propagules are mostly moved on the initial f lood tide and strand at the high tide mark less than 500 m from the po int of their release. Buoyancy of the propagules, tides and currents m ainly determine patterns of seedlings within undisturbed mangrove stan ds. Observations of propagules washed onto beaches show that most stra nd within 1 km of an estuary, and very few propagules were observed to disperse more than 10 km. Dispersal between populations is likely to be a rare event in southeastern Australia because of low numbers of fl oating propagules, the discontinuous distribution of habitat and the h azards of recruitment. This has two consequences: first, it may restri ct gene flow among populations; second, recovery from mass mortality w ithin an estuary will be slow.