Variation in t ~ 1 3 C values for the seagrass Thalassia testudinum and its relations to mangrove carbon

Lin, G., Banks, T. and Sternberg, LO., 1991. Variation in 5~3C values of the seagrass Thalassia testudinum and its relations to mangrove carbon. Aquat. Bot., 40: 333-341. Carbon isotope ratios (~3C/t2C) were measured for the leaves of the seagrass Thalassia testudinum Banks ex K/Snig and carbonates of shells collected at the seagrass beds from seven sites along the coast of southern Florida, U.S.A. The 5~3C values of seagrass leaves ranged from 7 . 3 to 16.3%0 among different study sites, with a significantly lower mean value for seagrass leaves from those sites near mangrove forests ( 12.8 +_ 1.1%0) than those far from mangrove forests ( 8.3 +_ 0.9%o; P< 0.05 ). Furthermore, seagrass leaves from a shallow water area had significantly lower 5 ~ 3C values than those found in a deep water area (P<0.01) . There was no significant variation in 5~3C values between young and mature leaves (P= 0.59 ) or between the tip and base of a leaf blade (P= 0.46 ). Carbonates of shells also showed a significantly lower mean 5~3C value in the mangrove areas ( 2.3 +_ 0.6%0) than in the non-mangrove areas (0.6+_0.3%o; P<0.025). In addition, the 5~3C values of seagrass leaves were significantly correlated with those of shell carbonates (5~3C seagrass l e a f = 9.1+ 1.3 ~3C shell carbonate (R2=0,83, P<0.01 ) ). These results indicated that the input of carbon dioxide from the mineralization of mangrove detritus caused the variation in carbon isotope ratios of seagrass leaves among different sites in this study.