Seagrass meadows provide critical ecosystem services but are increasingly threatened by coastal eutrophication from excessive nitrogen inputs. Seagrass response to nitrogen inputs may depend on species and background nutrient environments. This study examines the effects of elevated NH₄⁺ and NO₃⁻ concentrations on the physiological responses of common seagrass species Halophila ovalis and Cymodocea rotundata from two different locations in Singapore. The northern Johor Straits are more eutrophic due to river discharge and aquaculture activities, while the southern Singapore Straits are less eutrophic due to stronger tidal flushing. Seagrass plants were collected from the field and treated to water column dosing of NH4+ (0.0029 – 0.0274mg/L) over eight weeks in mesocosm set-up. Separately, in the subsequent eight weeks, the same experimental set-up with NO₃⁻ (0.0029 – 0.051mg/L) dosing was conducted with a fresh batch of plants. Physiological responses (e.g., Shoot count, leaf-area index, and photosynthetic efficiency) were assessed weekly. Seagrasses from southern straits responded more to nutrient enrichment; Fertilization effects were observed at lower nutrient dosages, while mortality was increased at higher nutrient dosages. The findings are relevant for coastal management as they help inform the thresholds for nutrient loads into coastal areas with seagrass meadows.