Science methods

 

The Science behind the Grades

How the data is collected for the Wet Tropics Report Card

The nine rivers in the Wet Tropics all flow east to the Great Barrier Reef. They are affected by a range of pressures including urban and agricultural development. The Report Card uses three indices to assess their condition:

Water quality Habitat & hydrology Fish

Water quality is important to aquatic ecosystem health, drinking water supply, agricultural use and recreation and cultural activities. The Report Card uses three categories of indicators to assess the condition of water quality:

Sediment Nutrients Pesticides

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Sediment

Sediment affects the reef and also freshwater ecosystem health. Levels of sediment are linked to erosion caused by land management practices.

Indicator

Total suspended solids (TSS) is a measure of the small particles in the water. Changing levels of TSS affect the clarity of the water which reduces the light for aquatic plants. It also smothers coral and other marine life and can signify a problem with normal sediment processes of the ecosystem.

Where

Sediments are sampled at the lowest end of the systems before it becomes estuarine. Details of site locations for each basin is provided on the basin’s web page and in the methods technical report.

When

During the dry season water samples are taken every month but they are taken more frequently (up to hourly) during high flow events in the wet season when water quality characteristics can change rapidly.

How

Water quality samples are collected using either manual grab sampling or automatic samplers. TSS concentrations are analysed in a lab. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Nutrients

Concentrations of nutrients in freshwaters are affected by land management practices and by point sources such as waste water treatment plants. High levels of nutrients can cause an increase in plants such algae, which smother coral and seagrass.

Indicators

Dissolved inorganic nitrogen (DIN) (eg. from urea) is used as crop fertiliser and in excess it can disturb the balance of aquatic ecosystems eg. by causing some organisms to grow faster such as algae. The Wet Tropics region contributes the highest annual DIN load to the GBR.

Filterable reactive phosphorus (FRP): High levels of phosphorus are associated with outbreaks of potentially toxic blue-green algae and blocking light for other aquatic plants.

Where

Nutrients are sampled at the lowest end of the systems before it becomes estuarine. Details of site locations for each basin is provided on the basin’s web page and in the methods technical report.

When

During the dry season water samples are taken every month but they are taken more frequently (up to hourly) during high flow events in the wet season when water quality characteristics can change rapidly.

How

Water quality samples are collected using either manual grab sampling or automatic samplers. DIN and FRP concentrations are analysed in a lab. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Pesticides

Pesticides can impact the health of freshwaters and are identified as a risk to the health of the reef. Some forms can persist in the environment for years.

Indicator

Pesticide risk metric: The Report Card currently assesses the risk posed of 22 pesticides to freshwater ecosystems. High concentrations of pesticides can impact on aquatic plants and animals.

Where

Pesticides are sampled at the lowest end of the systems before it becomes estuarine. Details of site locations for each basin is provided on the basin’s web page and in the methods technical report.

When

Sampling of pesticides occurs during the wet season when mobilisation and risk to aquatic ecosystems increases with rainfall-runoff events.

How

Water quality samples are collected using either manual grab sampling or automatic samplers. The risks are assessed based on exposure periods and concentrations.

This index gives an indication of how land use and development are impacting the health of aquatic systems and communities.

Habitat modification Flow Riparian vegetation Wetlands Invasive weeds

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Habitat modification

This refers to physical alterations in waterways (eg scouring or deposition of sediment), which can disrupt ecological processes and species distribution and behaviour.

Indicators

Impoundment length refers to the proportion of a river that has been pooled by construction of dams and weirs. Within the impoundment the water becomes deeper and slower flowing and aquatic plants and animals become more similar to those in a lake and less like the naturally occurring populations.

Fish barriers: Waterway barriers, such as causeways and weirs, impact the movement of the many migratory fish of the Wet Tropics. This can affect spawning, feeding and fish numbers.

Where

Anywhere where a weir or dam has been built on a stream. The basin fish barrier indicator is under development.

When

Every four years

How

GIS and satellite imagery are used to identify and measure impoundment length. Total length of impounded waterways is expressed as a proportion of total waterway length.

Flow

Flow assesses how closely current flows resemble pre-development flows. Natural water flows are important for waterway health but are affected by changes from urban development and agriculture eg. dams.

Indicators

10 measures of natural flow (eg. flood frequency and duration) are used to compare current flows with pre-development.

Changes in these patterns can disrupt aquatic processes and communities.

Where

DNRME flow gauging stations within each basin (some basins have multiple stations).

When

Every year

How

Measured flow is compared with modelled pre-development flow condition to determine the extent that flow has been impacted.

Riparian vegetation

Vegetation on the banks of waterways provides important bank and instream habitat. It also affects water quality by stabilising river banks, filtering coarse sediment and moderating water temperature from shading (good for fish).

Indicator

Riparian extent is a measure of the remaining streambank vegetation compared to pre-clearing. Healthy riparian vegetation reduces sediments and nutrients flowing into waterways. This indicator does not assess condition of riparian vegetation.

Where

Entire area of each basin.

When

Every four years

How

The 2009 Queensland Wetland Mapping Programme data is used to determine the extent of riparian vegetation and is compared against the pre-clearing extent.

Wetlands

The wetlands indicator assesses palustrine wetlands (swamps). These are an important habitat for a range of species but they also benefit water quality by retaining sediment and nutrients.

Indicator

Wetland extent measures how much natural wetland is remaining compared to pre-clearing. Healthy wetlands trap sediment and nutrients and support aquatic biological communities.This indicator does not assess condition of wetlands.

Where

Entire area of each basin.

When

Every four years

How

Queensland Regional Ecosystem version 5 wetlands mapping is used to determine the extent of palustrine wetlands compared to pre-clearing extent.

Invasive weeds

Invasive aquatic weeds reduce the abundance and diversity of native plant species, modify habitat for native fauna species, block and choke waterways, increase sedimentation and organic loading, decrease water quality and modify hydrology.

Indicator

Extent, diversity and impact: The invasive weed indicator maps the presence of aquatic weeds and assesses their impact on the waterway. Some invasive species are more harmful than others, which is taken into account.

Where

Entire area of each basin.

When

Every four years

How

Queensland Wetland Mapping was used to assess the presence and absence of aquatic weeds. Each weed species was scored according to its potential impact upon waterways.

Fish are an important indicator of the health of freshwater ecosystems. The Wet Tropics has the highest diversity of freshwater fish species in Australia but they can be impacted by poor water quality, flow regulation, degraded habitat and pressure from fishing.

Native fish Pest fish

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Native fish

The assessment of freshwater fish communities is based on the richness of native species and the abundance of pest fish.

Indicators

Proportion of observed vs expected species compares the current diversity of native species to the expected diversity in the absence of human pressures. This enables us to determine which species have been impacted and the nature of impacts occurring within basins.

Where

Russell and Mulgrave basins. Fish monitoring is being expanded to other basins.

When

Every four years

How

Fish are surveyed at approximately 15 sites within each basin using back pack and boat-based electrofishing during the dry season.

The species richness of native fish actually captured in 2018 and 2019 was compared with the expected species richness predicted by pre-disturbance models. The percentage of expected species was converted to a score based on standardised percent ranges, as with other indicators.

The proportion of pest fish recorded during field surveys was compared with the expected proportion of pest fish species based on a Queensland-wide model and the percentage was converted to a score using the standardised percent ranges.

Pest species

The assessment of freshwater fish communities is based on the richness of native species and the abundance of pest fish.

Indicators

Proportion pest fish measures the presence of pest fish compared to the expected number. Pest fish affect aquatic plants and animals by competing for food and space, preying on native species, introducing exotic diseases and parasites and driving habitat changes.

Where

Russell and Mulgrave basins. Fish monitoring is being expanded to other basins.

When

Every four years

How

Fish are surveyed at approximately 15 sites within each basin using back pack and boat-based electrofishing during the dry season.

The species richness of native fish actually captured in 2018 and 2019 was compared with the expected species richness predicted by pre-disturbance models. The percentage of expected species was converted to a score based on standardised percent ranges, as with other indicators.

The proportion of pest fish recorded during field surveys was compared with the expected proportion of pest fish species based on a Queensland-wide model and the percentage was converted to a score using the standardised percent ranges.

The eight estuaries in the Wet Tropics are affected by a range of pressures including urban and agricultural development, treated waste water release, fishing and water resource development. The Report Card uses three indices to assess their condition: water quality, habitat & hydrology and fish. Note: the fish index requires additional monitoring and is not currently reported.

Water quality Habitat & hydrology

Water quality is important to ecosystem health as well as recreational and cultural activities. The Report Card uses four categories of indicators to assess the condition of water quality: chlorophyll-a, nutrients, physico-chemistry and pesticide levels.

Chlorophyll-a Nutrients Physical-chemical Pesticides

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Chlorophyll-a

Chlorophyll-a concentration provides an estimate of algal biomass. High algal biomass typically occurs if nutrient concentrations are excessive.

Indicators

Chlorophyll-a is measure of algal biomass. High algal biomass is a strong indicator of elevated nutrient levels. Low flows and warmer conditions can combine with nutrients to cause impacts such algal or aquatic weed blooms.

Where

Chlorophyll-a is monitored at several locations within each estuary to represent the whole estuary. Details of site locations for each estuary are provided on the estuaries web page and in the methods technical report.

When

Samples are taken every month in the Daintree, Moresby and Hinchinbrook Channel but less frequently in the other estuaries. Details of the monitoring frequency for each estuary are provided in the methods technical report.

How

Water quality samples are collected using either in-situ measurements, grab sampling or automatic sampling. Chlorophyll-a concentrations are analysed in a laboratory. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Nutrients

Nutrient concentrations in estuaries are potentially affected by land management practices and by point sources such as wastewater treatment plants. High levels of nutrients can cause an increase in the growth of noxious algae and aquatic weeds.

Indicators

Dissolved organic nitrogen (DIN) is found in crop fertiliser and sometimes in treated wastewater. Excess amounts can disturb the balance of aquatic ecosystems by causing excessive growth of algae. This in turn can affect dissolved oxygen and food chains.

Filterable Reactive Phosphorus: Phosphorus is another component of crop fertilisers and wastewater effluent. High levels of phosphorus indicate poor land management, over fertilisation or wastewater impacts.

Where

Nutrients are monitored at several locations within each estuary to represent the whole estuary. Details of site locations for each estuary are provided on the estuaries web page and in the methods technical report.

When

Samples are taken every month in the Daintree, Moresby and Hinchinbrook Channel but less frequently in the other estuaries. Details of the monitoring frequency for each estuary are provided in the methods technical report.

How

Water quality samples are collected using either in-situ measurements, grab sampling or automatic sampling. Nutrient concentrations are analysed in a laboratory. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Physical-chemical

Basic physical and chemical parameters are commonly used indicators of water quality and can often be monitored directly. For example, temperature, electrical conductivity and pH. The physical-chemical indicators used to assess Wet Tropics estuaries are turbidity and dissolved oxygen.

Indicators

Turbidity is a measure of the amount of particulate material in the water. High turbidity is often associated with poor land management, erosion or nutrient enrichment.

Dissolved Oxygen (DO) concentrations are important to the health of aquatic biota. Low concentrations can result in fish kills and stress on other organisms. Organic matter from poor land use, high water temperatures and high levels of algae can all affect dissolved oxygen.

Where

Physical chemical indicators are monitored at several locations within each estuary to represent the whole estuary. Details of site locations for each estuary are provided on the estuaries web page and in the methods technical report.

When

Samples are taken every month in the Daintree, Moresby and Hinchinbrook Channel but less frequently in the other estuaries. Details of the monitoring frequency for each estuary are provided in the methods technical report.

How

Water quality samples are collected using either in-situ measurements, grab sampling or automatic sampling. Turbidity is measured in-situ. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Pesticides

Pesticides can impact the health of estuaries and are identified as a risk to the health of the reef. Some forms can persist in the environment for many years.

Indicators

Pesticide risk matrix: The Report Card currently assesses the risk posed by 22 different pesticides to estuarine ecosystems. High concentrations of pesticide can impact on aquatic plants and animals and/or accumulate in food chains.

Where

Pesticides are sampled in lowland freshwaters or within estuaries. The sites are those used for basins. Details of site locations is provided on the estuaries web page and in the methods technical report

When

Sampling of pesticides occurs during the wet season when mobilisation and risk to aquatic ecosystems increases with rainfall-runoff events.

How

Water quality samples are collected using either manual grab sampling or automatic samplers and are analysed in a laboratory. The risks are assessed based on exposure periods and concentrations.

This index gives an indication of how land use and development are impacting the health of aquatic systems and communities.

Fish barriers Flow Riparian vegetation Mangrove and saltmarsh Seagrass

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Fish barriers

Physical barriers such as causeways, road culverts and weirs, impact the movement of migratory fish with implications for spawning, feeding and fish recruitment.

Indicators

Fish barrier measures: Barriers are assessed on distance from the estuary and the degree to which they disrupt fish movement.

Where

Anywhere where a weir or dam has been built or a culvert installed.

When

Every four years

How

Mapping is used to identify potential barriers. Each one is assessed in the field according to a list of criteria.

Flow

This category assesses how closely current flows resemble natural flows. Seasonal flow patterns are important for waterway health but are affected by changes from urban development and agriculture, especially dams.

Indicators

Flow measures: 10 measures of natural flow (e.g. flood frequency and duration) are used to compare current flows with pre-development. Changes in these patterns can disrupt aquatic processes and communities.

Where

DNRME flow gauging stations upstream of each estuary.

When

Every year

How

Measured flow is compared with modelled pre-development flow to determine the extent that flow has been impacted.

Riparian vegetation

Streambank vegetation provides instream and fringing habitat. It also improves water quality by stabilising banks, filtering coarse sediment and cooling temperatures by shading.

Indicators

Riparian extent is a measure of the remaining streambank vegetation compared to pre-clearing. Healthy riparian vegetation reduces sediments and nutrients flowing into waterways. This indicator does not assess condition of riparian vegetation.

Where

Entire area of each estuary.

When

Every four years

How

The 2017 Queensland Wetland Mapping Programme data is used to determine the extent of riparian vegetation and is compared against the pre-clearing extent.

Mangrove and saltmarsh

Mangrove and saltmarsh vegetation filters and purifies water and is critical for estuarine ecosystem function habitat. These systems also play a major role in trapping carbon.

Indicators

Mangrove and saltmarsh extent measures how much is remaining compared to pre-clearing. Healthy mangroves and saltmarsh trap sediment and nutrients and support aquatic biological communities. This indicator does not assess condition.

Where

Entire area of each estuary.

When

Every four years

How

Queensland Regional Ecosystem version 5 wetlands mapping is used to determine the mangrove and saltmarsh extent compared to pre-clearing.

Seagrass

Seagrass provides nursery habitat for fish and crustaceans and is an important food source for dugongs and sea turtles. It also cycles nutrients, stabilises sediment, improves water quality and acts as a carbon sink.

Indicators

Seagrass health measures: Seagrass health is measured on biomass, area and species composition at selected monitoring meadows.

Where

Seagrass are currently monitored in Trinity Inlet and Moresby estuaries.

When

Every year

How

Queensland Ports Seagrass Monitoring Program is used to assess the health of seagrass meadows by aerial surveys compared to benchmarks from long term monitoring.

 

The inshore marine environment includes coral reefs, seagrass meadows, coral cays and islands in the coastal and mid-shelf marine areas. They are affected by a range of pressures including land use, coastal development, ports, tourism, shipping and fishing. The Report Card uses three indices to assess their condition: water quality, coral and seagrass. A fourth index (fish) is in development. There is currently insufficient monitoring and data for its inclusion in the Report Card.

Water quality Coral Seagrass

Water quality is important to aquatic ecosystem health as well as recreational and cultural activities. The Report Card uses four categories of water quality indicator: chlorophyll a, nutrients, water clarity and pesticides.

Chlorophyll-a Nutrients Water clarity Pesticides

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Chlorophyll-a

Chlorophyll-a is a pigment present in algae. High concentrations indicate excessive algal growth as a result of nutrient loads.

Indicators

Chlorophyll-a: Under natural conditions a shortage of nutrients prevents algae concentrations from building up. Chlorophyll-a is a convenient and effective way to measure algae levels.

Where

Chlorophyll-a is monitored at multiple locations within the North Central, South and Palm Island inshore zones.

When

Regular samples are taken throughout the year and in some instances are monitored continually by automatic loggers. Details of the frequency of monitoring is provided in the results technical report.

How

In-situ measurements, grab sampling and automatic loggers are used to assess inshore water quality. Water samples are analysed for chlorophyll-a in a laboratory. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Nutrients

Concentrations of nutrients in inshore waters are influenced by land use including agricultural and urban development. High levels of nutrients can cause an increase in plants such as algae and upset natural ecological processes.

Indicators

Oxidised nitrogen (NOx) (nitrite and nitrate) comes from crop fertilisers. Excess amounts can disturb the balance of aquatic ecosystems by causing excessive growth of algae and noxious aquatic weeds.

Particulate nitrogen (PN) (nitrite and nitrate) is nitrogen that is not dissolved and is found in or on particles such as sediment and algae. It is a measure of the total nitrogen that might become available for use by algae and aquatic plants.

Particulate phosphorus (PP) measures the phosphorus content that is not dissolved and is found in or on particles such as sediment and algae. It is a measure of the total phosphorus that might become available for use by algae and aquatic plants.

Where

Nutrients are monitored at multiple locations within the North Central, South and Palm Island inshore zones.

When

Regular samples are taken throughout the year and in some instances are monitored continually by automatic loggers. Details of the frequency of monitoring is provided in the results technical report.

How

In-situ measurements, grab sampling and automatic loggers are used to assess inshore water quality. Water samples are analysed for nutrients in a laboratory. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Water clarity

Water clarity is a measure of light penetration, which is needed for coral and seagrass survival. It is impacted by sediment loads and excessive algal growth.

Indicators

Turbidity is a measure of water clarity. Water that holds lots of sediment or algae has a high turbidity and hence low clarity.

Total suspended solids (TSS) is a measure of the small particles in the water, which affects water clarity. It is slightly different to turbidity in that it doesn’t measure the tiniest particles (called colloids).

Where

Indicators are monitored at multiple locations within the North Central, South and Palm Island inshore zones, although turbidity is not included in the northern zone.

When

Regular samples are taken throughout the year and in some instances are monitored continually by automatic loggers. Details of the frequency of monitoring is provided in the results technical report.

How

In-situ measurements, grab sampling and automatic loggers are used to assess inshore water quality. Water samples are analysed for TSS in a laboratory. Annual water quality scores are calculated from monthly data using scheduled water quality guidelines.

Pesticides

Pesticides are toxic and persistent chemicals that affect the health and diversity of aquatic organisms.

Indicators

Pesticide risk matrix: The Report Card currently assesses the risk posed by 22 pesticides to biological communities in inshore marine ecosystems. High concentrations of pesticides can impact on aquatic plants and animals.

Where

Pesticides are sampled at one or two fixed locations in each inshore marine zone.

When

Sampling of pesticides occurs year- round via passive samplers.

How

Passive samplers are replaced every 1-2 months, with the old sampler being taken to a laboratory for analysis.

Information used in this table was sourced from Johnson (2014).

Healthy coral reefs are critical to inshore marine communities and ecosystem processes and are affected by range of disturbances and impacts. The Report Card uses five categories of indicator to assess coral condition: coral cover, macroalgae cover, rate of coral cover increase, density of juvenile corals and community composition.

Coral cover Macroalgae cover Rate of coral cover increase Density of juvenile corals Community composition

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Coral cover

Healthy reef systems have a high degree of coverage by growing coral. Conversely, coral cover can be affected by floods, cyclones, bleaching and Crown of Thorns Starfish.

Macroalgae cover

Macroalgae can out-compete corals and can impact on reproduction, recruitment and growth. High proportions of macroalgae cover indicate an imbalance in the system.

Rate of coral cover increase

Healthy reef systems exhibit growth and also recover better from disturbance events Systems under stress from water quality and other factors show negative growth. The rate of increase in coral cover is an important indicator of health.

Density of juvenile corals

Reefs that have a high juvenile coral survival rate are able to recover more rapidly from disturbance events such as cyclones, floods and bleaching

Community composition

Healthy reef systems exhibit a diversity of coral species, while systems under stress may lose some of the more sensitive corals.

Where

Surveys are conducted at 4-7 sites within each zone. Details of the sites are provided in the methods technical report.

When

Surveys are undertaken bi-annually with additional surveys undertaken if disturbances are suspected.

How

Corals are surveyed using the manta tow and SCUBA search techniques while reef communities are assessed using underwater digital photography and counts of juvenile corals.
Scores are calculated by comparing survey results to baseline values representative of healthy and resilient coral communities.

Much of the information provided in this table was sourced from Thompson et al. 2017

Seagrass is an important habitat for a range of marine life and plays a major role in ecosystem health. It is impacted by coastal development, flooding, storm events, dredging and changes to water quality. The Report Card uses three categories of indicators to assess seagrass condition: abundance, reproduction and tissue nutrients.

Abundance Reproduction Tissue nutrients

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Abundance

The overall abundance of seagrass is highest when conditions (particularly water clarity) are favourable. A reduction in the abundance of seagrass meadows can indicate a period of prolonged poor water quality.

Indicators

Meadow area: The size (area) of seagrass meadows changes naturally in response to conditions, increasing when water quality is good and contracting after extended periods of poor water quality. This indicator measures the area of seagrass meadow during the monitoring period and allows us to monitor change over time.

Where

Seagrass condition is monitored at sites within the North and South zones. The location of sites within in each zone is provided in the methods technical report.

When

Seagrass is monitored every year in the late dry (growing) season and the late wet season. Late dry season results capture seagrass health during those months when conditions are usually favourable whilst late wet season captures information about meadows that may have been subject to poor water quality due to floods and cyclones.

How

Data is collected by the Marine Monitoring Program (MMP) and the Queensland Ports Seagrass Monitoring Program using in-field visual assessments, benthic cores and leaf tissue samples. Reproduction and tissue nutrients are analysed in the lab and compared to baseline data.

Reproduction

Healthy seagrass meadows can be affected by short term impacts such as storms and floods, but healthy systems usually recover and re-establish fairly quickly. This indicator is a measure of the resilience of seagrass meadows to recover from disturbances such as cyclones.

Indicators

Biomass is the weight of seagrass per unit of area. Meadows that are healthy and growing have a lot of plants per square metre and therefore a high biomass. In meadows affected by adverse conditions the mass of seagrass plants per square metre is often reduced.

Where

Seagrass condition is monitored at sites within the North and South zones. The location of sites within in each zone is provided in the methods technical report.

When

Seagrass is monitored every year in the late dry (growing) season and the late wet season. Late dry season results capture seagrass health during those months when conditions are usually favourable whilst late wet season captures information about meadows that may have been subject to poor water quality due to floods and cyclones.

How

Data is collected by the Marine Monitoring Program (MMP) and the Queensland Ports Seagrass Monitoring Program using in-field visual assessments, benthic cores and leaf tissue samples. Reproduction and tissue nutrients are analysed in the lab and compared to baseline data.

Tissue nutrients

The amount of nutrients contained within the seagrass tissue provides an indication of whether the meadow is stressed by poor water quality, the condition of the seagrass and whether the meadow is expanding or contracting.

Indicators

Species compotision Healthy seagrass communities typically have a diversity of different species. Meadows that are dominated by a smaller number of fairly tolerant usually indicate adverse conditions, whilst those with a higher diversity and the presence of more sensitive species usually indicate more favourable conditions in the leadup to monitoring.

Where

Seagrass condition is monitored at sites within the North and South zones. The location of sites within in each zone is provided in the methods technical report.

When

Seagrass is monitored every year in the late dry (growing) season and the late wet season. Late dry season results capture seagrass health during those months when conditions are usually favourable whilst late wet season captures information about meadows that may have been subject to poor water quality due to floods and cyclones.

How

Data is collected by the Marine Monitoring Program (MMP) and the Queensland Ports Seagrass Monitoring Program using in-field visual assessments, benthic cores and leaf tissue samples. Reproduction and tissue nutrients are analysed in the lab and compared to baseline data.

Information in this table is sourced from McKenzie et al. 2017 and York and Rasheed 2017.

The Offshore marine environment extends to the boundary of the Great Barrier Reef Marine Park along the coast of the Wet Tropics NRM region. It is impacted by Crown-of-Thorns Starfish (COTS) outbreaks, extreme floods, cyclones, coral bleaching and fishing. The Report Card uses two indices to assess offshore condition: water quality and coral. A third index (fish) requires additional monitoring data that are not currently collected.

Water quality Coral

Water quality is important for aquatic ecosystem health and for recreational and cultural activities. The Report Card uses two categories of water quality indicator at offshore marine sites: chlorophyll a, and water clarity.

Chlorophyll-a Water clarity

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Chlorophyll-a

This indicator category is representative of algae levels since chlorophyll a is a pigment present in algae. High concentrations are a common symptom of enrichment from excess nutrients from agriculture, storm runoff and wastewater release. When this occurs, light penetrating to coral, seagrass and other aquatic life is reduced.

Indicators

Chlorophyll-a: Ambient concentrations of chlorophyll a are natural quite low so if concentrations are high due to excessive algal growth it indicates that nutrient loading is upsetting the natural balance.

Where

Across the entire area of the offshore zone using satellite imagery.

When

Monitored continuously throughout the year.

How

Using cloud-free daytime imagery which is processed to obtain estimates of in-water optical properties and concentrations of optically active constituents.

Water clarity

Water clarity is a measure of light penetration, which is needed for coral survival. It is impacted by sediment loads and excessive algal growth. Events such as cyclones, storms and extreme floods can cause reduced clarity.

Indicators

Total suspended solids (TSS) is a measure of small particles suspended in the water, which affects light penetration and water clarity. When TSS is high but chlorophyll-a concentrations are low it suggests that the particles have come from land sources or from disturbance of marine sediments by wind and waves.

Where

Across the entire area of the offshore zone using satellite imagery.

When

Monitored continuously throughout the year.

How

Using cloud-free daytime imagery which is processed to obtain estimates of in-water optical properties and concentrations of optically active constituents.

Healthy coral reefs are critical to the Wet Tropics marine ecosystem, providing habitat, biodiversity and supporting ecosystem processes. Coral condition is affected by a range of disturbances and impacts such as bleaching, poor water quality, cyclones and recreational use. The Report Card uses three categories of indicator to assess coral condition: coral cover, rate of coral cover increase and density of juvenile corals.

Coral cover Rate of coral cover increase Density of juvenile corals

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Coral cover

Coral cover is a measure of the proportion of reef covered by live coral at a given time and is one of the most tangible and visible disturbance indicators of offshore reefs. In mature, healthy, undisturbed reef systems, coral cover tends to be relatively high and stable. A slow decline in coral cover over time can be the result of prolonged adverse conditions. Sudden loss may occur after floods, cyclones, bleaching events or outbreaks of Crown of Thorns Starfish.

Rate of coral cover increase

This indicator differs from coral cover in that it’s a measure of the rate of change in coral cover over time. Healthy coral reef systems are resilient and those that have experienced coral loss due to cyclones or floods can show high rates of coral growth afterwards as they recover. Reefs under stress may take longer to recover and show lower rates of coral cover increase. Coral reef systems experiencing a negative rate of growth in the absence of an extreme weather event may be under stress from prolonged periods of poor water quality.

Density of juvenile corals

The survival rate of juvenile corals is a good indicator of the resilience of the reef in the event of a disturbance event. Reefs with a high survival rate of juvenile coral indicate favourable conditions and good resilience. Those with lower survival rates may be slow to recover following cyclones, floods or bleaching events.

Where

Surveys are conducted at 15 sites across the offshore marine zone. Details of site locations are provided in the methods technical report.

When

Alternate years.

How

Coral surveys are undertaken using the manta tow and SCUBA search techniques. Surveys of benthic reef communities using underwater digital photography and counts of juvenile corals. Scores are calculated by comparing survey results to baseline values representative of healthy and resilient coral communities

Information used in this table was sourced from Thompson et al. 2017

 

 

References

Thompson, A., Costello, P., Davidson, J., Logan, M., Coleman, G., Gunn, K., Schaffelke, B., 2017, Marine Monitoring Program. Annual Report for inshore coral reef monitoring: 2015 to 2016. Report for the Great Barrier Reef Marine Park Authority, Great Barrier Reef Marine Park Authority, Townsville.133 pp.