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 !inurn and Ulva rigida, the dominant algae in Peel Inlet, Western Australia. Both species had ratesaturating mechanisms of phosphate uptake described by Michaelis-Menten type functions; C. !inurn had the faster uptake rate (667 c. f. 272Jlg P g dwC 1 h-1 ) although U. rigida had a lower half-saturation value. Both species displayed linear relationships between ammonium uptake rates and substrate concentrations with C. !inurn having the greater slope (4.4 c. f. 1.7). Chaetomorpha !inurn also had a linear increase in uptake rate with increasing concentration of nitrate, but U. rigida showed rate-saturating kinetics; below 750 Jlg L -1 , U. rigida had the higher rate of uptake. Ulva rigida had critical tissue nitrogen and phosphorus concentrations of 20 and 0.25 mg g dwC 1 respectively. Corresponding concentrations for C. !inurn were 12 and 0.5 mg g dwC 1 • 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. The growth rate of Ulva is negative in winter due to low salinity, temperature and irradience, and this results in negligible biomass at the time of highest inorganic nitrogen concentration. Chaetomorpha !inurn persists over winter allowing it to take advantage of elevated nutrient concentrations at the time; nutrients stored during winter support high growth rates in summer. The maximum tissue nitrogen levels recorded for Ulva were only 47% higher than the critical concentration while maximum tissue phosphorus concentration was almost 9 times the critical level. This seasonal limitation by nitrogen supports an earlier hypothesis that production in the system may be nitrogen limited in summer. It was concluded that differences in nutrient requirements and aquisition strategies afforded C. !inurn greater competitive potential for utilizing the seasonal and short-term increases in nutrient concentrations that occur in Peel Inlet.

Nutrient control of estuarine macroalgae:growth strategy and the balance between nitrogen requirements and uptake

“…Subsistence quotas and critical tissue N conccntrations resembled data from the literature (e.g. Hanisak 1979, Gordon et al 1981, Fujita et al 1989, Lavery & McComb 1991. With the exception of Chaeton~orpha linum, ephemeral species had slightly higher subsistence cell quotas and critical N concentrations than slow-growing species and, hence, species-specific N requirements to support maximum growth became several-fold larger among fast-than slow-growing macroalgae This suggests that fast-growing species face a higher risk of N limitation when exposed to low N concentrations, unless their requirements are met by proportionally faster N uptake.…”

Short-term nutrient pulses enhance growth and photosynthesis of the coral reef macroalga Sargassum baccularia

“…The N and P storage capacity of S. baccularia is about 4, which is slightly higher than values available for a range of temperate and tropical macroalgae (calculated from data compiled in Lobban & Harrison 1994). However, much higher values are reported for the chlorophyte Chaetomorpha linurn, which formed a macroalgal bloom in an estuary in southwest Australia (Lavery & McComb 1991). The capacity to utilise stored nutrients to sustain growth over a prolonged period of time when nutrient availability is low may be a competitive advantage of macroalgae over phytoplankton and opportunistic epiphytes.…”

Regulation of spatial and seasonal variation of macroalgal biomass in a brackish, eutrophic lake

“…Critical values determined for Ulva spp. range from 2.0% to 2.4% DW (Fujita et al 1989;Lavery and McComb 1991;Pedersen 1994). As tissue N levels of Ulva spp.…”