The Nutritional Eco-physiology of Chaetomorpha linum and Ulva rigida in Peel Inlet, Western Australia

Abstract

The uptake rates and critical tissue concentrations of nitrogen and phosphorus were determined for Chaetomorpha linum and Ulva rigida , the dominant algae in Peel Inlet, Western Australia. Both species had rate-saturating mechanisms of phosphate uptake described by Michaelis-menten type functions; C. linum had the faster uptake rate (667 c.f. 272 mu g P g/dwt/h) although U. rigida had a lower half-saturation value. Both species displayed linear relationships between ammonium uptake rates and substrate concentrations with C. linum having the greater slope (4.4 c.f. 1.7). Chaetomorpha linum also had a linear increase in uptake rate with increasing concentration of nitrate, but U. rigida showed rate-saturating kinetics; below 750 mu g/L, U. rigida had the higher rate of uptake. Ulva rigida had critical tissue nitrogen and phosphorus concentrations of 20 and 0.25 mg g/dwt respectively. Corresponding concentrations for C. linum were 12 and 0.5 mg g/dwt. Ulva is frequently nitrogen limited during spring in Peel Inlet, reflecting the high nitrogen requirements of this plant compared to Chaetomorpha as well as the reduced ability of Ulva to store nutrients over winter.