Spatial variation in phenolic content of seagrass thalassia hemprichii along Dar es Salaam coast

Phenolic compounds are good biomarkers of environmental disturbances. These compounds have been studied in few seagrasses species of marine ecosystems in the temperate region, but very little has been done to investigate the use of phenolic compounds as biomarkers of environmental disturbances along the coast of Dar es Salaam Indian Ocean. In this study, Thalassia hemprichii were collected from four different sites having different levels of anthropogenic perturbation namely, Ocean Road, Mjimwema, Kunduchi and Oysterbay during dry and rainy seasons. The total phenol contents of both above and belowground parts of the seagrass were determined using Folin-Ciocalteu method. The significant differences in total phenol were observed among sites in both above and below ground parts. High mean total phenol was recorded in dry season than in the rainy season.The mean total phenol in the below and above ground parts varied from 10.5 ± 1.6 to 84.8 ± 9.4 and 8.9 ± 1.9 to 21.7 ± 2.8 µg GAE / mg in dry season while the above and below ground parts in rainy season varied from 27.5 ± 3.7 to 48.5 ± 4.2 µg GAE / mg and 5.4 ± 0.6 to 17.7 ± 1.9 µg GAE / mg, respectively. Generally, in all sites the belowground parts possessed higher concentration of total phenol than aboveground parts in both seasons. There was significant negative correlation between total phenol and nitrate concentration in the water column (r = -0.95) and (r = -0.94) during dry and rainy seasons, respectively. The findings of this study shows that total phenol content is a potential early warning biological marker for assessing the status of seagrass meadows subjected to multiple environmental pressures as evidenced from studied sites.