Physiological responses of the seagrass Thalassia hemprichii (Ehrenb.) Aschers as indicators of nutrient loading

- We examined bioindicators of the seagrass Thalassia hemprichii to nutrient loading.
- Apparent two nutrient gradients were found in the Xincun Bay seagrass meadow.
- The P% of the plant almost mirrored the two nutrient gradients in the meadow.
- The epiphytic algae biomass and N% reflected one of the two nutrient gradients.
- The P% of T. hemprichii may be the most useful indicator of nutrient loading.

To select appropriate bioindicators for the evaluation of the influence of nutrients from human activities in a Thalassia hemprichii meadow, environmental variables and plant performance parameters were measured in Xincun Bay, Hainan Island, South China. Nutrient concentrations in the bay decreased along a gradient from west to southeast. Moreover, the nutrients decreased with an increase in the distance from the shore on the southern side of the bay. Among the candidate indicators, the P content of the tissues closely mirrored the two nutrient loading gradients. The epiphytic algae biomass and the N content in the tissues mirrored one of the two nutrient loading trends. The leaf length, however, exhibited a significant negative correlation with the nutrient gradients. We propose that changes in the P content of T. hemprichii, followed by epiphytic algae biomass and N content of the tissues, may be the useful indicators of nutrient loading to coastal ecosystems.