The takeover of Thalassia testudinum by Anadyomene sp. at Biscayne Bay, USA, cannot be simply explained by competition for nitrogen and phosphorous.

Apart from direct light effects, we tested whether the takeover of the seagrass Thalassia testudinum by the seaweed Anadyomene sp. in high nutrient areas of Biscayne Bay, Florida, USA, is related to a faster nutrient surge uptake capacity of the seaweed and/or a negative effect on the seagrass uptake rates. Anadyomene sp. and T. testudinum showed a similar ammonium surge uptake capacity, but the seagrass performed better than the seaweed in mixed incubations at high ammonium concentrations. T. testudinum was faster than Anadyomene sp. at taking up pulses of phosphate, but the uptake rates of the seagrass were significantly decreased in the presence of the seaweed. The takeover of T. testudinum by Anadyomene sp. at Biscayne Bay is likely dominated by light and cannot be simply explained by their single or mixed nutrient surge uptake rates, but the phosphate availability and the seagrass uptake inhibition by the seaweed may also play a key role in the process.