Variation in biogeochemical parameters across intertidal seagrass meadows in the central Great Barrier Reef region

This survey provides baseline information on sediment characteristics, porewater, adsorbed and plant tissue nutrients from intertidal coastal seagrass meadows in the central region of the Great Barrier Reef World Heritage Area. Data collected from 11 locations, representative of intertidal coastal seagrass beds across the region, indicated that the chemical environment was typical of other tropical intertidal areas. Results using two different extraction methods highlight the need for caution when choosing an adsorbed phosphate extraction technique, as sediment type affects the analytical outcome. Comparison with published values indicates that the range of nutrient parameters measured is equivalent to those measured across tropical systems globally. However, the nutrient values in seagrass leaves and their molar ratios for Halophila ovalis and Halodule uninervis were much higher than the values from the literature from this and other regions, obtained using the same techniques, suggesting that these species act as nutrient sponges, in contrast with Zostera capricorni. The limited historical data from this region suggest that the nitrogen and phosphorus content of seagrass leaves has increased since the 1970s concomitant with changing land use practice.     

Water quality in the inshore Great Barrier Reef lagoon: Implications for long-term monitoring and management

Coastal and inshore areas of the Great Barrier Reef lagoon receive substantial amounts of material from adjacent developed catchments, which can affect the ecological integrity of coral reefs and other inshore ecosystems. A 5-year water quality monitoring dataset provides a 'base range' of water quality conditions for the inshore GBR lagoon and illustrates the considerable temporal and spatial variability in this system. Typical at many sites were high turbidity levels and elevated chlorophyll a and phosphorus concentrations, especially close to river mouths. Water quality variability was mainly driven by seasonal processes such as river floods and sporadic wind-driven resuspension as well as by regional differences such as land use. Extreme events, such as floods, caused large and sustained increases in water quality variables. Given the highly variable climate in the GBR region, long-term monitoring of marine water quality will be essential to detect future changes due to improved catchment management.     

Polycyclic aromatic hydrocarbons in sediments of the Great Barrier Reef region,Australia

At present the concentrations of polycyclic aromatic hydrocarbons in sediments from the Great Barrier Reef are remarkably low. The baseline levels range from <0.01 μg kg^?1 dry wt. for benzo(k)fluoranthene and benzo(a)pyrene to <0.82 μg kg^?1 for chrysene. Measurable levels of polycyclic aromatic hydrocarbons have only been found in small areas close to sites frequently visited by power boats. Sediments from Townsville and Gladstone Harbours on the coast adjacent to the reef are polluted with polycyclic aromatic hydrocarbons to a similar degree to that reported for coastal sediments in similar locations in other parts of the world.     

Water quality monitoring: a combined approach to investigate gradients of change in the Great Barrier Reef, Australia

For the managers of a region as large as the Great Barrier Reef, it is a challenge to develop a cost effective monitoring program, with appropriate temporal and spatial resolution to detect changes in water quality. The current study compares water quality data (phytoplankton abundance and water clarity) from remote sensing with field sampling (continuous underway profiles of water quality and fixed site sampling) at different spatial scales in the Great Barrier Reef north of Mackay (20 degrees S). Five transects (20-30 km long) were conducted from clean oceanic water to the turbid waters adjacent to the mainland. The different data sources demonstrated high correlations when compared on a similar spatial scale (18 fixed sites). However, each data source also contributed unique information that could not be obtained by the other techniques. A combination of remote sensing, underway sampling and fixed stations will deliver the best spatial and temporal monitoring of water quality in the Great Barrier Reef.     

Seagrass population dynamics and water quality in the Great Barrier Reef region: a review and future research directions

Seagrasses in the Great Barrier Reef region, particularly in coastal habitats, act as a buffer between catchment inputs and reef communities and are important habitat for fisheries and a food source for dugong and green turtle. Within the Great Barrier Reef region there are four different seagrass habitat types now recognised. The spatial and temporal dynamics of the different types of seagrass habitat is poorly understood. In general seagrass growth is limited by light, disturbance and nutrient supply, and changes to any or all of these limiting factors may cause seagrass decline. The capacity of seagrasses to recover requires either recruitment via seeds or through vegetative growth. The ability of seagrass meadows to recover from large scale loss of seagrass cover observed during major events such as cyclones or due to anthropogenic disturbances such as dredging will usually require regeneration from seed bank. Limited research into the role of pollutants on seagrass survival suggests there may be ongoing impacts due to herbicides, pesticides and other chemical contaminants. Further research and monitoring of seagrass meadow dynamics and the influence of changing water quality on these is needed to enhance our ability to manage seagrasses on the Great Barrier Reef.     

Water quality and coral bleaching thresholds: Formalising the linkage for the inshore reefs of the Great Barrier Reef, Australia

The threats of wide-scale coral bleaching and reef demise associated with anthropogenic climate change are widely known. Here, the additional role of poor water quality in lowering the thermal tolerance (i.e. bleaching ‘resistance’) of symbiotic reef corals is considered. In particular, a quantitative linkage is established between terrestrially-sourced dissolved inorganic nitrogen (DIN) loading and the upper thermal bleaching thresholds of inshore reefs on the Great Barrier Reef, Australia. Significantly, this biophysical linkage provides concrete evidence for the oft-expressed belief that improved coral reef management will increase the regional-scale survival prospects of corals reefs to global climate change. Indeed, for inshore reef areas with a high runoff exposure risk, it is shown that the potential benefit of this ‘local’ management imperative is equivalent to ∼2.0-2.5 °C in relation to the upper thermal bleaching limit; though in this case, a potentially cost-prohibitive reduction in end-of-river DIN of >50-80% would be required. An integrated socio-economic modelling framework is outlined that will assist future efforts to understand (optimise) the alternate tradeoffs that the water quality/coral bleaching linkage presents.     

Monitoring pesticides in the Great Barrier Reef

Pesticide runoff from agriculture poses a threat to water quality in the world heritage listed Great Barrier Reef (GBR) and sensitive monitoring tools are needed to detect these pollutants. This study investigated the utility of passive samplers in this role through deployment during a wet and dry season at river mouths, two near-shore regions and an offshore region. The nearshore marine environment was shown to be contaminated with pesticides in both the dry and wet seasons (average water concentrations of 1.3-3.8 ng L⁻¹ and 2.2-6.4 ng L⁻¹, respectively), while no pesticides were detected further offshore. Continuous monitoring of two rivers over 13 months showed waters flowing to the GBR were contaminated with herbicides (diuron, atrazine, hexazinone) year round, with highest average concentrations present during summer (350 ng L⁻¹). The use of passive samplers has enabled identification of insecticides in GBR waters which have not been reported in the literature previously.     

Adaptive management and its role in managing Great Barrier Reef water quality

Adaptive management is the pathway to effective conservation, use and management of Australia's coastal catchments and waterways. While the concepts of adaptive management are not new, applications involving both assessment and management responses are indeed limited at the national and regional scales. This paper outlines the components of a systematic framework for linking scientific knowledge, existing tools, planning approaches and participatory processes to achieve healthy regional partnerships between community, industry, government agencies and science providers to overcome institutional barriers and uncoordinated monitoring. The framework developed by the Coastal CRC (www.coastal.crc.org.au/amf/amf/_index.htm) is hierarchical in the way it displays information to allow associated frameworks to be integrated, and represents a construct in which processes, information, decision tools and outcomes are brought together in a structured and transparent way for adaptive catchment and coastal management. This paper proposes how an adaptive management approach could be used to benefit the implementation of the Reef Water Quality Protection Plan (RWQPP).     

Water quality guidelines for the Great Barrier Reef World Heritage Area: a basis for development and preliminary values

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC Guidelines) provide default national guideline values for a wide range of indicators of relevance to the protection of the ecological condition of natural waters. However, the ANZECC Guidelines also place a strong emphasis on the need to develop more locally relevant guidelines. Using a structured framework, this paper explores indicators and regional data sets that can be used to develop more locally relevant guidelines for the Great Barrier Reef World Heritage Area (GBRWHA). The paper focuses on the water quality impacts of adjacent catchments on the GBRWHA with the key stressors addressed being nutrients, sediments and agricultural chemicals. Indicators relevant to these stressors are discussed including both physico-chemical pressure indicators and biological condition indicators. Where adequate data sets are available, guideline values are proposed. Generally, data were much more readily available for physico-chemical pressure indicators than for biological condition indicators. Specifically, guideline values are proposed for the major nutrients nitrogen (N) and phosphorus (P) and for chlorophyll-a. More limited guidelines are proposed for sediment related indicators. For most agricultural chemicals, the ANZECC Guidelines are likely to remain the default of choice for some time but it is noted that there is data in the literature that could be used to develop more locally relevant guidelines.     

Terrestrial pollutant runoff to the Great Barrier Reef: An update of issues, priorities and management responses

The Great Barrier Reef (GBR) is a World Heritage Area and contains extensive areas of coral reef, seagrass meadows and fisheries resources. From adjacent catchments, numerous rivers discharge pollutants from agricultural, urban, mining and industrial activity. Pollutant sources have been identified and include suspended sediment from erosion in cattle grazing areas; nitrate from fertiliser application on crop lands; and herbicides from various land uses. The fate and effects of these pollutants in the receiving marine environment are relatively well understood. The Australian and Queensland Governments responded to the concerns of pollution of the GBR from catchment runoff with a plan to address this issue in 2003 (Reef Plan; updated 2009), incentive-based voluntary management initiatives in 2007 (Reef Rescue) and a State regulatory approach in 2009, the Reef Protection Package. This paper reviews new research relevant to the catchment to GBR continuum and evaluates the appropriateness of current management responses.     

Tidal currents in the central Great Barrier Reef

Observations at 8 sites in the outer central Great Barrier Reef show M₂, S₂, K₁, and O₁ tidal currents flow directly off-shelf (northeast), when the corresponding tide at Townsville is at zero height and falling, with typical amplitudes of 12, 6, 3, and 2 cm s^?1. On the slope (at 300 m depth), the vertically averaged long-shelf component was small. On the shelf, the eccentricity of the tidal ellipses decreases shoreward and the tidal ellipses rotate anticlockwise. The major axes of the tidal ellipses tilt left of cross-shelf, especially for the diurnal constituents. There is satisfactory agreement between the observed and modelled cross-shelf currents. The long-shelf velocity is sensitive to the long-shelf changes in amplitude and phase of the tide heights and high quality tidal data for open boundary conditions will be required if numerical models are to model these currents satisfactorily.     

Comparing bleaching and mortality responses of hard corals between southern Kenya and the Great Barrier Reef, Australia

We compared the bleaching and mortality response (BMI) of 19 common scleractinian corals to an anomalous warm-water event in 1998 to determine the degree of variation between depths, sites, and regions. Mombasa corals experienced a greater temperature anomaly than those on the Great Barrier Reef (GBR) sites and this was reflected in the greater BMI response of most taxa. Comparing coral taxa in different sites at the same depth produced high correlation coefficients in the bleaching response in Kenya at 2 m (r=0.86) and GBR at 6 m depth sites (r=0.80) but less in the GBR for shallow 2 m sites (r=0.49). The pattern of taxa susceptibility was remarkably consistent between the regions. Coral taxa explained 52% of the variation in the response of colonies to bleaching between these two regions (Kenya BMI=0.90 GBR BMI+26; F(1,19) - 18.3; p < 0.001; r2 = 0.52). Stylophora and Pocillopora were consistently susceptible while Cyphastrea, Goniopora Galaxea and Pavona were resistant in both regions. Three taxa behaved differently between the two regions; Acropora, and branching Porites were both moderately affected on the GBR but were highly affected in Kenya while the opposite was true for Pavona. These results suggest that a colonies response to bleaching is phylogenetically constrained, emphasizing the importance of features of the host's physiology or morphology in determining the response to thermal stress.     

Trace metals in corals from the Great Barrier Reef

Various octocorallian and scleractinian corals from within the Great Barrier Reef Province were analysed for zinc, copper, cadmium, nickel and lead by atomic absorption spectroscopy. Of the two coral groups, the octocorals accumulated significantly greater amounts of all detectable metals. The soft coral, Sarcophyton sp., revealed distinct inter-locational differences for zinc, copper and cadmium. The potential of this genus for monitoring trace metal pollution in tropical reef waters is briefly discussed.     

Long-term sea-level variations in the central Great Barrier Reef

Low frequency sea-level variations and associated geostrophic currents in the central Great Barrier Reef (GBR) region near Townsville are studied using optimally-lagged multivariate regression. The analyses show that pressure-adjusted coastal sea levels and mid-shelf geostrophic currents are influenced predominantly by local along-shelf wind stress at the weather time-scale, and by climatic variables, such as atmospheric pressure and temperature, at seasonal and inter-annual time-scales. These forcing variables can specify sea levels over annual and inter-annual time-scales with a forecasting skill of 0.53 and 0.22, respectively (where 1.0 is perfect skill). Associated along-shelf geostrophic currents can be forecast with a skill of 0.57 over an annual time scale. If, instead, absolute coastal sea levels or offshore sea-level differences are used to specify the along-shelf geostrophic current, the forecasting skill is 0.75. A characteristic El Niño/Southern Oscillation (ENSO) response is detected for time periods up to 25 years in monthly sea-level both at Townsville and at western Pacific island sea-level stations. This spatially coherent response varies in intensity and phase within the Coral Sea. Sea-level differences show a pattern which characterizes known features of the large-scale circulation of the Coral Sea. These very low frequency sea-level variations in the Coral Sea must be taken into account to obtain accurate predictions of along-shelf geostrophic current variations on seasonal and inter-annual time scales. Regression analysis and a diagnostic river plume model show that the influence of the major rivers can produce sea-level changes due to buoyancy of order 5 cm. The corresponding errors in geostrophic velocities estimated using pressure-adjusted Townsville sea-level data alone are of order 5 cm s⁻¹ rms.     

Trace metals in algae from the Great Barrier Reef

Zinc, copper, cadmium, nickel, lead and mercury concentrations were examined in 48 species of algae from the Great Barrier Reef. In general the data showed considerable inter- and intra-specific variation with mean levels for each metal ranging from 0.27 to 38.6; 0.74 to 11.2; 0.08 to 2.2; 0.41 to 46.1; <0.45 to 6.7, and 0.005 to 0.320 μg g⁻¹ dry weight, respectively. Not-withstanding this, levels of all metals were substantially lower than reported values for algae from metal contaminated environments. The green alga, Chlorodesmis fastigiata, was the only species examined which was abundant at all study sites and, as a consequence, was considered to be the most suitable candidate for continued surveillance studies in the area.     

Changes in algal, coral and fish assemblages along water quality gradients on the inshore Great Barrier Reef

Macroalgae, hard corals, octocorals, and fish were surveyed on 10 to 13 inshore coral reefs of the Great Barrier Reef, along a water quality gradient in two regions with contrasting agricultural land use. A water quality index was calculated for each reef based on available data of particulate and dissolved nutrients, chlorophyll and suspended solids. Strong gradients in ecological attributes occurred along the water quality gradient. Macroalgae of the divisions Rhodophyta and Chlorophyta increased with increasing nutrients, while Phaeophyta remained similar. Octocoral richness and abundances of many hard coral and octocoral taxa decreased, and none of the hundreds of species increased. At reefs in higher nutrient environments, hard coral and octocoral assemblages were composed of subsets of the many species found in lower nutrient environments, whereas fish and macroalgal assemblages consisted of contrasting suites of species. The study identifies species groups that are likely to increase or decrease in abundance with changing water quality.     

Water Quality in the Great Barrier Reef World Heritage Area: Past Perspectives, Current Issues and New Research Directions

Elevated sediment and nutrient concentrations have long been regarded as the pre-eminent water quality threats to the Great Barrier Reef, with the potential risk posed by other pollutants such as heavy metals, persistent chlorohydrocarbons, PCBs and petroleum related compounds considered to be of lesser consequence. However, the management focus on these latter types of pollutants has recently shifted to acknowledge the potential impact posed by diuron, dioxins, dieldrin, and mercury and cadmium concentrations detected in sediments and biota along the Great Barrier Reef and southern Queensland coastline. In general, these threats originate from areas dominated by intensive cropping agriculture and are exacerbated by high rainfall and erosion rates in the wet tropics region of the Queensland coast. Maintenance of long-term monitoring programmes, which utilize innovative data acquisition techniques will enable assessment of change in environmentally relevant pollutant concentrations over time. However, improved land management practices, which include an immediate minimization of vegetation clearance and responsible use of pesticides and fertilizers in Queensland are essential if water quality in the Great Barrier Reef World Heritage Area is to be maintained and protected.     

In the other 90%: phytoplankton responses to enhanced nutrient availability in the Great Barrier Reef Lagoon

Our view of how water quality effects ecosystems of the Great Barrier Reef (GBR) is largely framed by observed or expected responses of large benthic organisms (corals, algae, seagrasses) to enhanced levels of dissolved nutrients, sediments and other pollutants in reef waters. In the case of nutrients, however, benthic organisms and communities are largely responding to materials which have cycled through and been transformed by pelagic communities dominated by micro-algae (phytoplankton), protozoa, flagellates and bacteria. Because GBR waters are characterised by high ambient light intensities and water temperatures, inputs of nutrients from both internal and external sources are rapidly taken up and converted to organic matter in inter-reefal waters. Phytoplankton growth, pelagic grazing and remineralisation rates are very rapid. Dominant phytoplankton species in GBR waters have in situ growth rates which range from approximately 1 to several doublings per day. To a first approximation, phytoplankton communities and their constituent nutrient content turn over on a daily basis. Relative abundances of dissolved nutrient species strongly indicate N limitation of new biomass formation. Direct ((15)N) and indirect ((14)C) estimates of N demand by phytoplankton indicate dissolved inorganic N pools have turnover times on the order of hours to days. Turnover times for inorganic phosphorus in the water column range from hours to weeks. Because of the rapid assimilation of nutrients by plankton communities, biological responses in benthic communities to changed water quality are more likely driven (at several ecological levels) by organic matter derived from pelagic primary production than by dissolved nutrient stocks alone.