Effects of prolonged shading stress on growth and survival of seagrass Posidonia australis in Jervis Bay, New South Wales, Australia

Spatial and temporal patterns of polychaete communities in 2 intertidal flats were examined in a subtropical mangrove swamp. Tan-Shui estuary, Taiwan from 1991 to 1993. The 2 sites appear a s distinct microhabitats, differing mainly in sediment granulometry, and consequently in community structure. The 'Creek' site was sandy (0.10 to 0.26 mm, 2 to 30% silt/clay content), while the 'River' site was muddy (0.06 to 0.14 mm, 16 to 60% silt/clay content). A total of 9 species were collected, with 6 species found at both sites. Indices of species diversity and evenness were greater at the Creek site than at the River site, but averaged denslty was 2 times lower (8317 vs 23 325 ind. Dominance a t the Creek site was shared by 2 to 3 species, whereas at the River site a single species, the sabellid Laonome albicingillun~, was domlnant Populat~on densities and phys~cal parameters were closely correlated. A4alacoceros lndicus occurred lvith large pal-tlcles, while L. dlbicingillum increased w.ith small grains. Population densities at both sltes va r~ed seasonally, but the timing for increases in densities was 1 to 2 mo earlier at the River slte. Effects of s h a d ~ n g by mangi-ove trees at the Creek site were the likely causes of such subtle differences. Abundance in t h ~ s wamp was greater than those in other tropical mangrove systems. The polychaete populations here may have experienced an environment which was not only nourished by sufficient detrital food, but was also less subject to fluctuation in terms of physical factors. L. albicingillum had high reproduct~ve rates, similar to those of opportunistic species, but differed in its large size and in its life history traits.