Poster: Education

Abs # 4: Low salinity responses measured by spectral reflectance of 4 seagrasses: Thalassia testidinum, Halodule wrightii, Suringodium filiforme and Zostera maritime

Presenter:	Thorhaug, Anitra , athorhaug@msn.com
Authors	Thorhaug, Anitra  (A)
Affiliations:	(A): Greater Caribbean Energy & Environment Foundation

Anthropomorphic salinity modification in estuaries is widespread decreasing seagrasses in many areas. This work is the first time spectral reflectance measurements have been used for measuring physiological processes in seagrasses. The spectral reflectance of four species of seagrasses (the subtropical/tropical Thalassia testudinum , Halodule wrightii, and Syringodium filiforme and the temperate Zostera maritime ) were measured as a function of decreased salinity ( within natural estuarine storm-induced limits) from 32 to 16 ppt over 308 to 1132 nm . The results of 24 hr exposure showed Thalassia, Halodule and Syringodium PRI ( Photochemical reflectance index ) and D750 were statistically significantly different ( P= 0.01) 32 ppt vs 16 ppt whereas Zostera reponses were not significantly different. Thalassia and Syringodium had large responses. This suggests a lower photosynthetic efficiency at lower salinities for the three species. Thalassia had significant differences after reduced salinity incubations in intermediate salinities seen in reflectance changes at 525nm and 650-680 nm suggesting changes in xanthophylls and chlorophylls. The structural-independent pigment index (SIPI) was higher in mature Thalassia blades at 16 than in new blades. The normalized difference vegetation index (NDVI) was reduced at 16 ppt from that at 32 ppt for mature blades, but increased slightly for new blades.Lethal salinity differences of Thalassia had already been established by one of us (AT) at 20ppt after 72 hr exposure.