Spatial differences were also detected for the d13C, although
these were less significant. Mussels grown at station R had 13C-depleted
tissues, possibly indicating an influence of terrestrial material
(d13C = 26% for terrestrial C3 detritus and 23% to 30% for
terrestrial C3 plants vs. 18% to 24% for phytoplankton and
3% to 15% for sea grasses) (Fry and Sherr, 1984). As this effect
is significant even during the dry period, we hypothesize that the
signature in this part of the bay is the result of 13C-depleted material
brought by rainy input and sediment. However, this hypothesis
must be verified by performing an isotopic analysis of the sediment
from different parts of the bay.