The intertidal distribution of the grey mangrove (Avicennia marina) in southeastern Australia: The effects of physical conditions, interspecific competition, and predation on propagule establishment and survival

Abstract

The upper and lower limits of the distribution of mature Avicennia marina lie between mean high water and mean sea level m open estuaries in southeastern Australia. Newly established seedlings are highly variable in abundance, but are rarely found in the saltmarsh or on mudflats. Their distribution is unlikely to be limited by dispersal because propagules disperse into the saltmarsh and to intertidal mudflats, but their establishment may be hmited by physicochemical conditions, interspecific competition and predation.The model that physicochemical conditions control the mtertidal limits of establishment of seedlings was accepted for propagules stranding in the saltmarsh but rejected for those stranding on mudflats. No seedlings established on saltmarsh sediments but similar numbers of seedlings established within light gaps in adult mangrove stands and on intertidal mudflats. The model that interspecific interaction with freelivmg macroalgae (Hormosira banksii) reduces the establishment of seedlings on mudflats covered with macroalgae or in stands with a ground cover of macroalgae was accepted. Under controlled conditions five times as many propagules established on cleared ground compared with ground covered with macroalgae. Predators also reduce seedling establishment, but the model that they preferentially act on propagules stranding on the mudflat was rejected. The low number of seedhngs found on mudflats without macroalgae appears to relate to wave and current efFects on establishment and the efFects of waterlogging or fouling on survival.

Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms

“…The majority of propagules remained within the lagoon and its adjacent channels, and often near the parental trees. Field experiments support these findings as modal or average propagule movement of Rhizophora and even Avicennia was found to be limited and concentrated near the parental trees, especially within mature forest stands (Clarke and Myerscough, 1993;De Ryck, 2009;McGuinness, 1997;Sousa et al, 2007). Water-buoyant propagules may set out to colonise and establish new stands but like in most plant species, they will rather strand in the vicinity of the parent trees to replenish existing stands (Duke et al, 1998;Harper, 1977;Levin et al, 2003;Sousa et al, 2007) with a higher chance of suitable environmental conditions.…”

Relationship between sediment conditions and mangrove Rhizophora apiculata seedling growth and nutrient status

“…High silt loads in the rivers cause increased sediment accretion and thus the formation of new habitat suitable for natural mangrove colonization and continuous development of extensive mangrove f0rest.s (Panapitukkul et al 1998). Our results show that increased siltation will enhance seedling growth, which likely helps the seedlings to outbalance the high mortality rates encountered by newly established unprotected seedlings (Clarke & Myerscough 1993). In order to promote mangrove progression and compensate for earlier losses of forest area, various programmes have been initiated to protect expanding mangrove fringes and afforestation programmes have also been conducted.…”

How do tree competition and stand dynamics lead to spatial patterns in monospecific mangroves?

“…They are fingerprints of important key factors, such as local competition 2804 M. N. I. Khan et al: Tree competition and stand dynamics lead to spatial patterns for photosynthetic light in the canopy (Clarke and Allaway, 1993;Khan et al, 2004), microtopography (DahdouhGuebas et al, 2007;Di Nitto et al, 2008), vegetation composition (Jayatissa et al, 2002;Kairo et al, 2002), sediment chemistry (Thiobodeau and Nickerson, 1986;Clarke and Allaway, 1993;McKee, 1995;Alongi et al, 2004), tidal elevation (Clarke and Myerscough, 1993), salinity (Clarke and Allaway, 1993;Krauss et al, 2008), dispersal patterns (Rabinowitz, 1978;Clarke and Myerscough, 1991;Clarke, 1993), and the competitive ability of species (Clarke and Myerscough, 1993;Berger andHildenbrandt, 2000, 2003;Canham et al, 2004).…”