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.