Hl. Hsieh et al., Detrital flows through the feeding pathway of the oyster (Crassostrea gigas) in a tropical shallow lagoon: delta C-13 signals, MARINE BIOL, 136(4), 2000, pp. 677-684
The spatial relationships and linkage of the detrital flows among the water
column, the sediment and the oyster Crassostrea gigas cultured in the wate
r column were examined by using stable carbon isotopes (delta(13)C) in a tr
opical shallow lagoon from October 1996 to June 1997. The lagoon is located
in southwestern Taiwan and is isolated from the sea by sand barriers excep
t at two tidal inlets. It receives freshwater mainly from two rivers. A tot
al of 12 stations were set up along three transect lines, each running acro
ss the lagoon from riverine to tidal inlet localities. The delta(13)C value
s of the water-column POM exhibited a marked sea-river gradient, with value
s depleted from a high of -21.7 parts per thousand at seaward stations to a
low of -28.2 parts per thousand at riverine stations; those in the sedimen
tary POM (< 62 mu m grain size) also revealed this trend, but to a lesser e
xtent. Oysters of two known ages, 6 months old ("old oysters") and newly se
ttled individuals ("young oysters"), were transplanted from one station to
each of the remaining stations, while some were left at the original statio
n. Values of delta(13)C in the muscle of transplanted oysters changed in pa
rallel with the sea-river gradient of delta(13)C in POM (decreasing from -1
6.0 to -18.5 parts per thousand in old oysters and from -16.8 to -21.9 part
s per thousand in young ones). The spatial sea-river gradient of the oyster
's delta(13)C is related not only to the distance between the site that the
oyster inhabits and sea or riverine environment, but also to the tidal flo
w pattern that surrounds its feeding place. Although the delta(13)C value o
f the sedimentary POM was correlated with that of the water-column POM, the
delta(13)C value of the oyster tissue was significantly correlated with th
at of the water-column POM, but not with that of the sedimentary POM. This
suggests that the oyster feeds primarily on water-column rather than sedime
ntary POM.