Coastal ecosystems continue to come under increasing pressure from human activities and the input of anthropogenic substances. This is being realised in a number of areas where eutrophic conditions begin to dominate and phenomena such as toxic algal blooms increase in frequency. Amidst this situation there is a growing need to understand how ecosystem components such as benthic fauna might respond to these conditions and how we might better use some of these components as indicators of ecosystem perturbation. In this context the current study examines the distribution and abundance of sediment meiofauna in seagrass beds at two different locations in Moreton Bay estuary. This ecosystem presently receives significant anthropogenic inputs from the Brisbane River and other sources draining the greater Brisbane catchment and adjoining areas. The main aims of the study were to characterise the distribution and abundance of meiofauna in these sediments and to also examine some of the main factors influencing these features. Also, it was intended that on examination be made of the influence that blooms of the cyanobacterium Lyngbya majuscula might have on meiofauna abundance and distribution in these areas. Blooms of this alga are an increasing feature of the Moreton Bay estuary and potentially represent a strong influence on a range of habitats and organisms within the ecosystem. In considering the physico-chemical aspects influencing meiofauna, sediment grain size and nutrient levels were shown to have some effect on distribution and abundance although this varied between species and location. Further, the grain size of the sediment and the total organic carbon did not change significantly between bloom and non-bloom periods and but total nitrogen and C/N ratio did show a change. In regard to the observed effects of the L. majuscula blooms, a negative impact was observed on copepod and nematode abundance and distribution. In both cases their abundance was considerably smaller during the bloom period. Notably, polychaetes showed no effect from the bloom?s occurrence. The results also indicate that during the bloom the meiofauna were distributing shallower in the sediment, probably due to the hypoxic conditions that the bloom may have created. Moreover, the impact of the bloom was more pronounced in the smaller size classes for the meiofauna and suggests that these classes are more sensitive to the conditions generated by the deposited bloom material. Under Multiple Regression Analysis nematodes and polychaetes were positively correlated with sediment nitrogen concentration, while copepods were not. Also, during the bloom the nitrogen concentration in the sediment increased but the abundance of nematodes showed an opposite trend. The general negative effect of the bloom on the total fauna might be the responsible for this result. An attempt was also made to assess whether the nematode:copepod ratio (Ne:Co) could be used in this ecosystem as an indicator of pollutant input or habitat disturbance by the algal bloom. This ratio has been used elsewhere with some success. Results from this study indicated that this ratio has only limited value as an indicator in the study situation and that the concomitant influence of sediment grain size and nutrient levels lead to a potentially misleading interpretation of the results that the ratio provides. The interactions between meiofauna, the prevailing physico-chemical and biological characteristics of the sediments in Moreton Bay are clearly very complex. The influence of phenomena such as the Lyngbya blooms adds to this complexity but, in the current study, this was seen to clearly have an effect on both animal abundance and their distribution. In this regard, the present study has identified the key areas of influence from the algal blooms and has also highlighted the need to further research these important animal groups so that we may better understand how the benthos, and thus the wider ecosystem, might cope with pollutants and anthropogenic disturbances.

Yes / A bidirectional synthesis of the originally proposed structures for the natural products elatenyne and a chloroenyne from Laurencia majuscula is described along with a reassessment of the structures of the halogenated enynes based upon a 13C NMR chemical shift/structure correlation / EPSRC

<p>Discoveries in recent years have disclosed the importance of marine cyano-bacteria in the context of primary production and global nitrogen cycling. It is hypothesized here that microbial mats in tropical coastal habitats harbour a rich diversity of previously uncharacterized cyanobacteria and that benthic marine nitrogen fixation in coastal zones is substantial.</p><p>A polyphasic approach was used to investigate cyanobacterial diversity in three tropical benthic marine habitats of different characters; an intertidal sand flat and a mangrove forest floor in the Indian Ocean, and a beach rock in the Pacific Ocean. In addition, nitrogenase activity was measured over diel cycles at all sites. The results revealed high cyanobacterial diversity, both morphologically and genetically. Substantial nitrogenase activity was observed, with highest rates at daytime where heterocystous species were present. However, the three habitats were dominated by non-heterocystous and unicellular genera such as <i>Microcoleus</i>, <i>Lyngbya</i>, <i>Cyanothece</i> and a large group of thin filamentous species, identified as members of the Pseudanabaenaceae family. In these consortia nocturnal nitrogenase activities were highest and <i>nifH</i> sequencing also revealed presence of non-cyanobacterial potential diazotrophs. A conclusive phylogenetic analysis of partial nifH sequences from the three sites and sequences from geographi-cally distant microbial mats revealed new clusters of benthic potentially ni-trogen-fixing cyanobacteria. Further, the non-heterocystous cyanobacterium <i>Lyngbya majuscula</i> was subjected to a physiological characterization to gain insights into regulatory aspects of its nitrogen fixation. The data demon-strated that nitrogenase activity is restricted to darkness, which called upon a re-evaluation of its diazotrophic behaviour.</p>

Discoveries in recent years have disclosed the importance of marine cyano-bacteria in the context of primary production and global nitrogen cycling. It is hypothesized here that microbial mats in tropical coastal habitats harbour a rich diversity of previously uncharacterized cyanobacteria and that benthic marine nitrogen fixation in coastal zones is substantial. A polyphasic approach was used to investigate cyanobacterial diversity in three tropical benthic marine habitats of different characters; an intertidal sand flat and a mangrove forest floor in the Indian Ocean, and a beach rock in the Pacific Ocean. In addition, nitrogenase activity was measured over diel cycles at all sites. The results revealed high cyanobacterial diversity, both morphologically and genetically. Substantial nitrogenase activity was observed, with highest rates at daytime where heterocystous species were present. However, the three habitats were dominated by non-heterocystous and unicellular genera such as Microcoleus, Lyngbya, Cyanothece and a large group of thin filamentous species, identified as members of the Pseudanabaenaceae family. In these consortia nocturnal nitrogenase activities were highest and nifH sequencing also revealed presence of non-cyanobacterial potential diazotrophs. A conclusive phylogenetic analysis of partial nifH sequences from the three sites and sequences from geographi-cally distant microbial mats revealed new clusters of benthic potentially ni-trogen-fixing cyanobacteria. Further, the non-heterocystous cyanobacterium Lyngbya majuscula was subjected to a physiological characterization to gain insights into regulatory aspects of its nitrogen fixation. The data demon-strated that nitrogenase activity is restricted to darkness, which called upon a re-evaluation of its diazotrophic behaviour.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.