P.R.F. Bell

Eutrophication and coral reefs—some examples in the Great Barrier Reef lagoon

Eutrophication or “nuisance” algal growth causes negative impacts on coral reefs via a number of routes and can eventually lead to the replacement of the coral community with various flora and fauna (e.g. attached algae, seagrasses and detrital/filter feeders). Chlorophyll a appears to be the best water quality indicator of eutrophication and a eutrophication threshold value at or below an annual mean of 0.5 mg m−3 is suggested. The concentrations of nutrients N and P associated with the onset eutrophication in coral reef communities are less well defined (annual mean DIN ∼ 1 μM; P-PO4 ∼ 0.1–0.2 μM) but are in accord with eutrophication threshold levels for sensitive freshwater ecosystems. The proliferation of nitrogen fixing algae in pristine coral reef regions highlights the importance of phosphorus and trace components such as Mo and Fe and even soluble organic matter to the overall primary production. The concentration of nutrients and levels of chlorophyll a in some regions of the Great Barrier Reef (GBR) lagoon are comparable to those that would be classed as eutrophic in other coral reef regions of the world. The available evidence points to riverine run-off as the cause of elevated P-PO4 levels in the inner lagoon. Historical evidence indicates that the levels of P-PO4 and phytoplankton growth, and particularly that of Trichodesmium spp, are relatively high in the river affected areas and that the levels may have significantly increased in the inner lagoon over the past 50–60 years. The nitrogen-fixing ability of Trichodesmium suggests that increased levels of P alone may be driving increased levels of primary productivity in the lagoon. It is hypothesized that the riverine-promoted eutrophication is a significant factor in the demise of fringing reefs in the inner GBR lagoon. The recorded levels of nano plankton growth in some river-affected regions of the GBR lagoon are sufficient to promote the survival of Acanthaster planci (crown of thorns starfish) larvae and as such eutrophication could well be a principal causative factor of the crown of thorns outbreaks. Elevated levels of nutrients and algal growth occur in some outer regions of the GBR but these appear to be due to natural phenomena. The high background concentrations of nutrients and phytoplankton in both the inner and outer GBR, whether they are natural or not, demands that special precautions be exercised in the control of sewage effluents and run-of in the vicinity of coral reefs.

Status of eutrophication in the Great Barrier Reef lagoon

Historical data on the levels of nutrients and phytoplankton in the GBR lagoon are reviewed. The results indicate that background levels of P-PO4 and phytoplankton have increased significantly over the past 50-60 years and that the levels appear be at or above the eutrophication threshold level for coral reef waters. Other data indicate that river discharge probably has a major impact on the nutrient status of the GBR lagoon, but other factors such the nitrogen-fixing blue-green alga, Trichodesmium, could also be important. Trichodesmium has the ability to introduce large amounts of new nitrogen and it appears that the increased phosphorus levels could be driving its growth. To-date little effort has been made to assess the impact of eutrophication on the coral reef communities. Because the background nutrient levels are relatively high both run-off and sewage discharges could have serious impacts on nearby coral reef communities. Tertiary treatment (i.e. nutrient removal) of sewage should be required for all discharges in the vicinity of coral reefs and special precautions need to be exercised when designing run-off drainage systems.

PHOSPHATE UPTAKE AND GROWTH KINETICS OF TRICHODESMIUM (CYANOBACTERIA) ISOLATES FROM THE NORTH ATLANTIC OCEAN AND THE GREAT BARRIER REEF, AUSTRALIA†

We compared inorganic phosphate (Pi) uptake and growth kinetics of two cultures of the diazotrophic cyanobacterium Trichodesmium isolated from the North Atlantic Ocean (IMS101) and from the Great Barrier Reef, Australia (GBRTRLI101). Phosphate‐limited cultures had up to six times higher maximum Pi uptake rates than P‐replete cultures in both strains. For strain GBRTRLI101, cell‐specific Pi uptake rates were nearly twice as high, due to larger cell size, but P‐specific maximum uptake rates were similar for both isolates. Half saturation constants were 0.4 and 0.6 μM for Pi uptake and 0.1 and 0.2 μM for growth in IMS101 and GBRTRLI101, respectively. Phosphate uptake in both strains was correlated to growth rates rather than to light or temperature. The cellular phosphorus quota for both strains increased with increasing Pi up to 1.0 μM. The C:P ratios were 340–390 and N:P ratios were 40–45 for both strains under severely P‐limited growth conditions, similar to reported values for natural populations from the tropical Atlantic and Pacific Oceans. The C:P and N:P ratios were near Redfield values in medium with >1.0 μM Pi. The North Atlantic strain IMS101 is better adapted to growing on Pi at low concentrations than is GBRTRLI101 from the more Pi‐enriched Great Barrier Reef. However, neither strain can achieve appreciable growth at the very low (nanomolar) Pi concentrations found in most oligotrophic regimes. Phosphate could be an important source of phosphorus for Trichodesmium on the Great Barrier Reef, but populations growing in the oligotrophic open ocean must rely primarily on dissolved organic phosphorus sources.

Factors affecting N2 fixation by the cyanobacterium Trichodesmium sp. GBRTRLI101

Abstract Various factors affecting N(2) fixation of a cultured strain of Trichodesmium sp. (GBRTRLI101) from the Great Barrier Reef Lagoon were investigated. The diurnal pattern of N(2) fixation demonstrated that it was primarily light-induced although fixation continued to occur for at least 1 h in the dark in samples that had been actively fixing N(2). N(2) fixation was dependent on the light intensity and stimulated more by white light when compared with blue, green, yellow and red light whereas rates of N(2) fixation decreased most under red light. Inorganic phosphorous concentrations in the lower range of treatments up to 1.2 muM significantly stimulated N(2) fixation and further additions promoted little or no increase in N(2) fixation. Organic phosphorous (Na-glycerophosphate) also stimulated N(2) fixation rates. Added combined nitrogen (NH(4) (+), NO(3) (-), urea) of 10 muM did not inhibit N(2) fixation in short-term studies (first generation), however it was depressed in the long-term studies (fifth generation).

Identification and treatability of organics in oil shale retort water

Analysis by GC-MS of the process water derived from Fischer Assay retoring of oil shale from Rundle, Australia has provided positive identification of the major organic constituents present. This is the first detailed analysis of retort water from Australian oil shales and showed that the compounds ranged from being highly biodegradable to highly inhibitory and resistant to biological oxidation. The major classes of compounds found in a composited sample included normal carboxylic acids, alkyl pyridines, quinolines and cyclic saturated and unsaturated ketones. Separation of the retort water into its acid, base and neutral fractions was brought about by solvent extraction using methylene chloride. A series of treatability studies on the retort water confirmed the hypothesis that only a portion of the organic carbon was amenable to biological treatment. In addition, high ammonia levels further inhibited biological action. Adsorption of the retort water with activated carbon proved most successful in removing the non-biodegradable fraction of the organic species. Chemical oxidation by ozone does not appear attractive because it lacks the specificity of adsorption.

Reevaluation of ENCORE: support for the eutrophication threshold model for coral reefs.

Abstract The results from the multimillion dollar Enrichment of Nutrients on Coral Reefs Experiment (ENCORE) on One Tree Island Reef (OTIR) suggest that increased nutrient loads to coral reefs will have little or no effect on the algal growth rates and, hence, on the associated effects that increased algal growth might have on the functioning and stability of coral reefs. However, a comparison of the concentrations of nutrients within the OTIR lagoon with the proposed nutrient threshold concentrations (NTC) for coral reefs suggests that all sites, including the control sites, were saturated with nutrients during ENCORE, and, hence, one would not expect to get any differences between treatments in the algal-growth related measurements. Thus, ENCORE results provide strong support for the proposed NTCs and support the ecological principle that algal productivity and, consequently, the functioning of coral reefs are sensitive to small changes in the background concentrations of nutrients. The principal conclusion of ENCORE, namely that the addition of nutrients did not cause the “pristine” OTIR to convert from coral communities to algal dominated reefs, is contrary to the fact that there was prolific macroalgal growth on the walls and crests of the experimental microatolls by the end of ENCORE.

Adsorption of pyridine onto spent Rundle oil shale in dilute aqueous solution

The adsorption of pyridine from aqueous solutions onto the solids generated by the processing of Rundle oil shale shows that the adsorption isotherm is of Langmuir type (L-4) with two plateaux. Cations which are leached from the spent shale or which are in retort water (Na, K, Ca, NH4) have a marked effect on the adsorption; the anion effect, while measurable, is much less. The adsorption is controlled by a number of factors such as pyridine co-ordination, surface protonation and ion exchange. XRD studies show that the montmorillonite in the spent shale expands during the sorption process, indicating a re-orientation of the adsorbed pyridine. The results identify some of the mechanisms likely to control the transport and removal of N-heterocyclic compound in spent shale waste dumps.

Quinoline adsorption onto combusted rundle spent shale in dilute aqueous solution at the natural pH 8

The adsorption of quinoline from aqueous solutions onto combusted Rundle spent shale shows that the adsorption isotherm is of Langmuir type (L-4). Cations which are leached from the spent shale or which are in retort water (Ca2+, Mg2+, Na+, K+, NH+4) have a marked effect on the adsorption. The sulphate anions have a small effect, while chloride anions have almost no effect on the adsorption. The adsorption of the base is mainly attributed to the formation of quinoline-metal ion complexes that result from coordination/protonation mechanisms rather than simply to cation exchange of the quinolinium ion. It is noted that this study did not attempt to delineate the relative importance of coordination and protonation mechanisms. Thus the two mechanisms are lumped together and regarded as an important property of the system. The ionic potential is used to scale the importance of coordination/protonation in the adsorption process. The mechanism of proton transfer to the quinoline molecule could be important for the adsorption of quinoline in ammonium solutions.

Laboratory culture studies of Trichodesmium isolated from the Great Barrier Reef Lagoon, Australia

Cultures of Trichodesmium from the Northern and Southern Great Barrier Reef Lagoon (GBRL) have been established in enriched seawater and artificial seawater media. Some cultures have been maintained with active growth for over 6 years. Actively growing cultures in an artificial seawater medium containing organic phosphorus (glycerophosphate) as the principal source of phosphorus have also been established. Key factors that contributed to the successful establishment of cultures were firstly, the seed samples were collected from depth, secondly, samples were thoroughly washed and thirdly, incubations were conducted under relatively low light intensities (PAR ∼ 40–50 μmol quanta m−2 s−1). N2 fixation rates of the cultured Trichodesmium were found to be similar to those measured in the GBRL. Specific growth rates of the cultures during the exponential growth phase in all enriched media were in the range 0.2–0.3 day−1 and growth during this phase was characterised by individual trichomes (filaments) or small aggregations of two to three trichomes. Characteristic bundle formation tended to occur following the exponential growth phase, which suggests that the bundle formation was induced by a lack of a necessary nutrient e.g. Fe. Results from some exploratory studies showed that filament-dominated cultures of Trichodesmium grew over a range of relatively low irradiances (PAR ∼ 5–120 μmol quanta m−2 s−1) with the maximum growth occurring at ∼ 40–50 μmol quanta m−2 s−1. These results suggest that filaments of the tested strain are well adapted for growth at depth in marine waters. Other studies showed that growth yields were dependent on salinity, with maximum growth occurring between 30 and 37 psu. Also the cell yields decreased by an order of magnitude with the reduction of Fe additions from 450 to 45 nM. No active growth was observed with the 4.5 nM Fe addition.

Effect of light on growth, pigmentation and N2 fixation of cultured Trichodesmium sp. from the Great Barrier Reef lagoon

The influence of light intensity and light quality on the growth, N2 fixation and pigmentation of cultures of the cyanobacterium Trichodesmium GBRTRLI101 were investigated under defined laboratory conditions. Both growth rate and N2 fixation rate were strongly dependent on light intensity. The N2 fixation rate increased with light intensity over the whole range tested (PAR 10–160 μmol quanta m−2 s−1) but the growth rate passed through a maximum in the range 45–75 μmol quanta m−2 s−1. Growth rates were the highest under white and yellow light and were significantly reduced under red light. The results also showed that the cellular concentrations of chlorophyll a and phycobiliproteins (PBPs) increased under low light conditions and were affected by light quality. Overall the results suggest that the availability of light and the quality of that light play an important role in the growth and distribution of Trichodesmium in coastal and oceanic waters.