h , rc (he viviparous seeds, which 

 linatc on the plant, fall on 10 the 

 gga,, modfi»tS. Few Of these sced- 

 ! sin vivo, however, and the 

 'Session of a rapid advance of 

 proves on to mudflats is mis- 

 Sg They persist only where 

 'invent accretion has recently 

 5ed the level of the mudflats m 

 ( ' [0llt 0 f the mangrove fringe. An 



Aainpte of ,ms ls sccn alon s sitlc tne 



\Z C |, ;i nks at Yaringa, where an area 

 f | 0Ca l recent accretion of mud 

 I mafksd out by mangroves that 

 ire n ow three or four years old 



I Plate 3). 



There arc other sectors where a 

 UMt advance of mangroves on to 

 n u„ilUits can be demonstrated, but 

 | 00g stretches of the mangrove fringe 

 .,, ull ul Western port Bay have not 

 a 4VftB0ecl at all between l£66 and 

 I'i7l. The physiological factors which 

 Ifolil seedling survival arc not 



known, but it is clear that mangroves 

 cannot spread forward until the mud- 

 flats in front of them have been 

 built up to a suitable level by sedi- 

 mentation. 



There is, nevertheless, one way in 

 which mangroves may contribute to 

 the build-up of adjacent mudflats, 

 and thereby prepare the way for their 

 own subsequent advance. The man- 

 grove fringe provides sheltered con- 

 ditions in the nearshore zone when 

 winds are blowing off the land during 

 high tides This was observed while 

 working in boats near the outer edge 

 of the mangroves: onshore winds 

 generate waves which wash sediment 

 into the mangroves (Plate 4). hut 

 offshore winds scarcely ripple the 

 water surface within a zone up lo 

 20 yards off the mangrove edge. 

 Where mangroves are not present. 

 Offshore winds generate currents 

 which can move sediment away from 



