Effects of phosphorus on the growth and nitrogen fixation rates of Lyngbya majuscula: implications for management in Moreton Bay, Queensland

Abstract

Significant acetylene reduction and therefore N 2 fixation was observed for Lyngbya majuscula only during dark periods, which suggests that oxygenic photosynthesis and N 2 fixation are incompatible processes for this species. Results from a series of batch and continuous-flow-culture reactor studies showed that the specific growth rate and N 2 fixation rate of L. majuscula increased with phosphate (P-PO 4 ) concentration up to a maximum value and thereafter remained constant. The P-PO 4 concentrations corresponding to the maximum N 2 fixation and maximum growth rates werẽ 0.27 and ~0.18 µM respectively and these values are denoted as the saturation values for N 2 fixation and growth respectively. Regular monitoring studies in Moreton Bay, Queensland, show that concentrations of P-PO 4 generally exceed these saturation values over a large portion of the Bay and therefore, the growth of the bloom-forming L. majuscula is potentially maximised throughout much of the Bay by the elevated P-PO 4 concentrations. Results from other studies suggest that the elevated P-PO 4 concentrations in the Bay can be largely attributed to discharges from waste-water treatment plants (WWTPs), and thus it is proposed that the control of the growth of L. majuscula in Moreton Bay will require a significant reduction in the P load from the WWTP discharges. If the current strategy of N load reduction for these discharges is maintained in the absence of substantial P load reduction, it is hypothesised that the growth of L. majuscula and other diazotrophs in Moreton Bay will increase in the future.

Mapping the distribution, biomass and tissue nutrient levels of a marine benthic cyanobacteria bloom (Lyngbya majuscula)

“…The high C : P and N : P ratios of L. majuscula in the current study support the contention experienced in earlier studies (Elmetri and Bell 2004;Albert et al 2005;Ahern et al in press) that L. majuscula growth rates in Deception Bay are influenced by phosphorus availability. The C : P ratios (415-691; 396-660 adjusted for carbonate) and N : P ratios (26-72) in the present study (Fig.…”

“…Thus, the high C : P ratios (combined with high N : P ratios and low phosphorus contents) of L. majuscula in the present study strongly support phosphorus limitation of L. majuscula in Deception Bay. Phosphorus has been shown to stimulate filament growth (Elmetri and Bell 2004;Ahern et al 2007), biomass growth (Ahern et al 2007) and nitrogen-fixation rates (Elmetri and Bell 2004;O'Neil et al 2004) of L. majuscula in the laboratory and to substantially increase biomass in field experiments at two locations in Moreton Bay: Eastern Banks (Ahern et al 2007) and Deception Bay (Ahern et al in press). …”

Effects of monsoon-driven wave action on coral reefs of Guam and implications for coral recruitment

“…Benthic cyanobacteria are quick 1.8 1.5 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec colonizers that are able to fix nitrogen and respond to phosphorous enrichment (Kuffner and Paul 2001;Elmetri and Bell 2004), are unpalatable to a variety of herbivores (Pennings et al 1997;Thacker et al 1997;Nagle and Paul 1999), and can bloom rapidly forming mats of fine filaments that overgrow and quickly dominate benthic communities (Cowell and Botts 1994;Doyle and Smart 1998;. Cyanobacteria can also inhibit coral recruitment even when appropriate substrate is available (Kuffner and Paul 2004).…”

Evidence of Large-Scale Chronic Eutrophication in the Great Barrier Reef: Quantification of Chlorophyll a Thresholds for Sustaining Coral Reef Communities

“…Laboratory studies (Elmetri and Bell 2004;Fu et al 2005) show that the N-fixation rates and growth rates of various diazotrophs common to the GBR are proportional to P-PO 4 concentrations in the low concentration range (\0.3 lM). Such diazotrophs can also have high requirements for some trace compounds such as iron (Fe).…”