This dataset summarises 30 years of seagrass data collection (1984-2014) within the Great Barrier Reef World Heritage
Area. The Site data describes seagrass at 66,210 sites; while the Meadow data describes seagrass at 1,169 individual or
composite meadows. The data includes information on species, meadow type and age and reliability of the data. The dataset
is available as shapefiles, GIS layer packages, and/or a CSV file. Data represented in this dataset has been collected by
the TropWATER Seagrass Group and CSIRO in a GIS database.
In making this data publicly available for management, the authors from the TropWATER Seagrass Group request being contacted
and involved in decision making processes that incorporate this data, to ensure its limitations are fully understood. The
site and meadow GIS available on eAtlas should be considered a “living” document that will be updated and modified as
new data become available.
A later version (2020) of this dataset including 35 years of data has been published under "Seagrass mapping synthesis:
A resource for coastal management in the Great Barrier Reef (NESP TWQ Project 3.2.1 and 5.4, TropWATER, James Cook University)."
The sampling methods used to study, describe and monitors seagrass meadows were developed by the TropWATER Seagrass Group
and tailored to the location and habitat surveyed; these are described in detail in the relevant publications (https://research.jcu.edu.au/tropwater).
Methods for data sets collected by CSIRO are reported in Pitcher et al (2007).
1. Location – Latitudes and longitudes are from converted RADAR fix or GPS. Depth is depth below mean sea level (dbMSL) in
2. Seagrass metrics – Visual estimation methods prior to 1990 were mostly percent cover estimates matched to standard photographs.
Data limitations for these early surveys are specific to each survey and advice from the TropWATER data custodians should
be sought for assistance with interpretation. For recent surveys (post-1990) above-ground biomass was determined using a
“visual estimates of biomass” technique (Mellors 1991) using trained observers. A linear regression was calculated for the
relationship between the observer ranks and the harvested values. This regression was used to calculate above-ground biomass
for all estimated ranks made from the survey sites. Biomass ranks were converted into above-ground biomass estimates in
grams dry weight per square metre (g DW m-2) for each site. Observers estimated biomass data using video transects, grabs,
free diving, helicopter and walking:
* Video transect: Commonly used for subtidal meadows at each transect site. A CCTV camera was lowered to the bottom and towed
at drift speed (less than one knot). Footage was observed on a TV monitor and digitally recorded. The recording was paused
at random times and frames selected. From this frame, an observer estimated a rank of seagrass biomass and a species composition.
On completion of the video analysis, the video observer ranked five additional quadrats that had been previously videoed
for calibration. The camera sled included a small collecting net to obtain a specimen for identification.
* van Veen grab: Commonly used for subtidal meadows. A sample of seagrass was collected using a van Veen grab (grab area
0.0625 m2) to identify species present at each site. Species identified from the grab sample were used to inform species
composition assessments made from the recorded video transects (Kuo and McComb 1989), or to record presence/absence where
visibility was too poor for video transects.
* Free diving, helicopter and walking: At each site seagrass above-ground biomass and species composition were estimated
from 0.25 m2 quadrats placed randomly. Seagrass percent cover was recorded at each site. The “visual estimates of biomass”
technique when applied to free diving/helicopter/walking surveys involves ranking while referring to a series of quadrat
photographs of similar seagrass habitats for which the above-ground biomass has been previously measured. The relative proportion
of the above-ground biomass (percentage) of each seagrass species within each survey quadrat was also recorded. Field biomass
ranks were converted into above-ground biomass estimates in grams dry weight per square metre (g DW m-2).
This section will document changes to the dataset as subsequent versions are released. This section will allow you to tell
if you have the latest copy of the dataset.
- Version 1 (2016-06-09): Initial release of the dataset containing data from 1984 - 2014. The filenames for this release
were: GBR_NESP-TWQ-3-1_JCU_Seagrass_1984-2014_Site-surveys and GBR_NESP-TWQ-3-1_JCU_Seagrass_1984-2014_Meadow-boundaries.
All survey data were entered into a Geographic Information System (GIS) using MapInfo (generally pre-2005) then ArcMap®
software. MapInfo spatial data was converted to ArcMap shapefiles. Rectified colour satellite imagery of the region (Source:
ESRI), field notes and aerial photographs taken from helicopter surveys were used to identify geographical features such
as reef platforms, channels and deep-water drop-offs to assist in determining seagrass meadow boundaries. Two GIS layers
- a Site layer and a Meadow layer - were created to describe seagrass. The projection used for these layers is GDA94.
* GBR_NESP-TWQ-3-1_JCU_Seagrass_1984-2014_Site-surveys.shp (Site surveys)
* GBR_NESP-TWQ-3-1_JCU_Seagrass_1984-2014_Meadow-boundaries.shp (Meadow boundaries)
Seagrass site Data:
1. Temporal survey details:
- MONTH/YEAR: Time of survey.
- SEASON: Whether the survey occurred in the growing (September to January) or senescent (February to August) season;
2. Spatial survey details
- LOCATION: Description of the location of the survey.
- NRM: The NRM region, where applicable, in which the survey occurred.
- LATITUDE/LONGITUDE: survey site.
- DEPTH: the site depth in metres below mean sea level (dbMSL).
3. Seagrass information:
- PRESENCE_A: the presence/absence of seagrass.
- DOMINANT_S: the dominant species, where recorded, at the survey site.
- C_ROTUNDAT: presence/absence of Cymodocea Rotundata at the site.
- C_SERRULAT: presence/absence of Cymodocea Serrulata at the site.
- E_ACOROIDE: presence/absence of Enhalus Acoroides at the site.
- H_CAPRICOR: presence/absence of Halophila Capricorni at the site.
- H_DECIPIEN: presence/absence of Halophila Decipiens at the site.
- H_OVALIS: presence/absence of Halophila Ovalis at the site.
- H_SPINULOS: presence/absence of Halophila Spinulosa at the site.
- H_TRICOSTA: presence/absence of Halophila Tricostata at the site.
- H_UNINERVI: presence/absence of Halodule Uninervis at the site.
- S_ISOETIFO: presence/absence of Syringodium Isoetifolium at the site.
- T_CILIATUM: presence/absence of Thalassodendron Ciliatum at the site.
- T_HEMPRICH: presence/absence of Thalassia Hemprichii at the site.
- Z_CAPRICOR: presence/absence of Zostera Muelleri subsp. Capricorni at the site.
4. Sampling methods:
- SURVEY_MET: helicopter, walking, boat with camera, diver, grab and/or sled
5. Data custodians:
- DATA_CUSTO: Data custodians
Seagrass meadow data:
- NRM_REGION: The NRM region in which the survey occurred.
- SURVEY_DAT: Survey month and year, or a list of survey dates for meadows repeatedly sampled.
- METHOD: Sampling and mapping methods – GPS/aerial photography, helicopter, walking, boat with camera, diver, grab and/or
- PERSISTENC: Meadows were classed according to four categories: Stable, Variable, Highly variable ephemeral, or Unknown.
- MEADOW_LOC: Meadows were classed according to three categories, although some meadows cover a range of these locations:
Intertidal, Shallow subtidal, or Deep subtidal.
- DENSITY: Meadow density categories (light, dense, variable among years, unknown) were determined by the consistency of
mean above-ground biomass of the dominant species among all years sampled.
- DOMINANT_S: Dominant species and species present.
- SPP_PRESEN: All species present.
- MEAN_BIOMA: Mean meadow biomass in g DW m-2 (+ standard error if available), or the minimum and maximum biomass recorded
for meadows sampled more than once.
- AREA_HA: Meadow area in hectares (+ reliability estimate if available), or the minimum and maximum area recorded for meadows
sampled more than once.
- HECTARES: Total extent of meadow (HA)
- PERCENT_CO: Meadow percent cover - this value represents mean seagrass percent cover, or the range of percent cover (if
>1 number in the data cell). Meadow percent cover was most commonly calculated in pre-1990s surveys and recorded as “n/a”
if not available.
- CUSTODIAN: Data custodians
- Stable: enduring meadow form; seagrass presence, biomass and area expected to be stable over time and seagrass meadow
expected to be a permanent feature apart from extreme events or sustained long term impacts;
- Variable: meadow presence, biomass and area expected to fluctuate within and among years, but generally some seagrass expected
to be present apart from extreme events or sustained long term impacts;
- Highly variable ephemeral: meadow not persistent over time; at some time periods seagrass will be present and at other
times absent. Ephemeral meadows that have a naturally extreme level of variation in area and biomass within and among years;
- Unknown: undetermined persistence as meadow sampled only once.
- Intertidal - all sites surveyed by helicopter or walking within a meadow and/or comments in field books identified an
- Shallow subtidal - meadows where free divers SCUBA, sled collection, or cameras were used to sample and water depth was
generally <10 m;
- Deep subtidal - for this project meadows >10 m deep were included as deep subtidal.
Seagrass data north and south of the GBRWHA were excluded from the layers but are available on request. Data were included
when sites and meadows extended west of the GBRWHA boundary into coastal and estuarine water immediately adjacent. In shallow
coastal waters seagrass meadows have been mapped and estimates of meadow boundaries are provided in the meadow GIS layer.
For deeper water seagrass information is provided as data points in the site layer. Modelled distributions are available
(Coles et al 2009; Pitcher et al 2007) but not included here.
Data included extends back to the mid-1980s. Large parts of the coast have not been mapped for seagrass presence since that
time. Technology and methods for mapping and position fixing have improved dramatically in 30 years. Early data included
here has been re-checked and re-entered on several occasions and previously included in other spatial platforms (see McKenzie
et al 2014). The layers included in this report represent the most reliable interpretation of that early data.
Seagrass taxonomy has changed through time, with species such as Halophila ovata no longer recognised and some doubts expressed
about other species whose morphology is relatively plastic. Field surveys have at times grouped species that are difficult
to distinguish outside a laboratory. To address these issues we have amalgamated some species into complexes: Halophila ovata,
Halophila minor, Halophila colesi/australis and Halophila ovalis are included as Halophila. ovalis. Halodule pinifolia is
grouped with Halodule. uninervis. Data collected in winter may underestimate the extent of ephemeral species such as Halophila
decipiens and Halophila tricostata. This is important if this composite is used to compare annual changes. Zostera muelleri
subsp. capricorni has been abbreviated to Zostera capricorni throughout.
TropWATER gives no warranty in relation to the data (including accuracy, reliability, completeness, currency or suitability)
and accepts no liability (including without limitation, liability in negligence) for any loss, damage or costs (including
consequential damage) relating to any use of the data. TropWATER reserves the right to update, modify or correct the data
at any time. The limitations of some older data included need to be understood and recognised. The TropWATER Seagrass Group
would appreciate the opportunity to review documents providing research, management, legislative or compliance advice based
on this data.
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This dataset is saved in the eAtlas enduring data repository at: data\NESP1\3.1_Seagrass-mapping