Four Decades of Seagrass Spatial Data from Torres Strait and Gulf of Carpentaria (NESP MaC Project 1.13, TropWATER JCU)

This dataset summarises 40 years of seagrass data collection (1983-2022) within Torres Strait and the Gulf of Carpentaria into two GIS shapefiles: (1) a point shapefile that includes survey data for 48,612 geolocated sites, and (2) a polygon geopackage describing seagrass at 641 individual or composite meadows.

Managing seagrass resources in northern Australia requires adequate baseline information on where seagrass is (presence/absence), the mapped extent of meadows, what species are present, and date of collection. This baseline is particularly important as a reference point against which to compare seagrass loss or change through time. The scale of northern Australia and the remoteness of many seagrass meadows from human populations present a challenge for research and management agencies reporting on the state of seagrass ecological indicators. Broad-scale and repeated surveys/studies of areas are logistically and financially impractical. However seagrass data is being collected through various projects which, although designed for specific reasons, are amenable to collating a picture of the extent and state of the seagrass resource.

In this project we compiled seagrass spatial data collected during surveys in Torres Strait and the Gulf of Carpentaria into a standardised form with point-specific and meadow-specific spatial and temporal information. We revisited, evaluated, simplified, standardised, and corrected individual records, including those collected several decades ago by drawing on the knowledge of one of our authors (RG Coles) who led the early seagrass data collection and mapping programs. We also incorporate new data, such as from photo records of an aerial assessment of mangroves in the Gulf of Carpentaria in 2017.
This project was funded by the National Environmental Science Programme (NESP) Marine and Coastal Hub and Torres Strait Regional Authority (TSRA) in partnership with the Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University. The project follows on from TropWATER’s previous work compiling 35 years of seagrass spatial point data and 30 years of seagrass meadow extent data for the Great Barrier Reef World Heritage Area (GBRWHA) and adjacent estuaries, funded through successive NESP Tropical Water Quality Hub Projects 3.1 (2015-2016) and 5.4 (2018-2020). These data sets are now publicly available through the eAtlas data portal: https://doi.org/10.25909/y1yk-9w85 . In making this data publicly available for management, the authors and data custodians request being contacted and involved in decision making processes that incorporate this data, to ensure its limitations are fully understood.

Methods:
The data were collected using a variety of survey methods to describe and monitor seagrass sites and meadows. For intertidal sites/meadows, these include walking, observations from helicopters in low hover, and observations from hovercraft when intertidal banks were exposed. For subtidal sites/meadows, methods included free diving, scuba diving, video transects from towed cameras attached to a sled with/without a sled net, video drops with filmed quadrats, trawl and net samples, and van Veen grab samples. These methods were selected and tailored by the data custodians to the location, habitat surveyed, and technology available. Important site and method descriptions and contextual information is contained in the original trip reports and publications for each data set provided in Table 1 of Carter et al. (2022).

Geographic Information System (GIS)
Mapping data for historic records (1980s) were transcribed from original logged and mapped data based on coastal topography, dead reckoning fixes and RADAR estimations. More recent data (1990’s onwards) is GPS located. All spatial data were converted to shapefiles with the same coordinate system (GDA 1994 Geoscience Australia Lambert), then compiled into a single point shapefile and a single polygon shapefile (seagrass meadows) using ArcMap (ArcGIS version 10.8 Redlands, CA: Environmental Systems Research Institute, ESRI). Some early spatial data was offset by several hundred metres and where this occurred data was repositioned to match the current coastline projection. The satellite base map used throughout this report is courtesy ESRI 2022.

Seagrass Site Layer:
This layer contains information on data collected at assessment sites, and includes:
1. Temporal survey details – Survey month and year;
2. Spatial position - Latitude/longitude;
3. Survey name;
4. Depth for each subtidal site is m below MSL Depth and was extracted from the Australian Bathymetry and Topography Grid, June 2009 (Whiteway 2009). This approach was taken due to inconsistencies in depth recordings among data sets, e.g., converted to depth below mean sea level, direct readings from depth sounder with no conversion, or no depth recorded. Depth for intertidal sites was recorded as 0 m MSL, with an intertidal site defined as one surveyed by helicopter, walking, or hovercraft when banks were exposed during low tide;
5. Seagrass information including presence/absence of seagrass, and whether individual species were present/absent at a site;
6. Dominant sediment - Sediment type in the original data sets were based on grain size analysis or deck descriptions. For consistency, in this compilation we include only the most dominant sediment type (mud, sand, shell, rock, rubble), removed descriptors such as “fine”, “very fine”, “coarse”, etc., and replaced redundant terms, e.g. “mud” and “silt” are termed “mud”;
7. Survey methods – In this compilation we have updated and standardised the terms used to describe survey methods from the original reports; and
8. Data custodians.

Seagrass Meadow Layer:
Polygons in the meadow layer are drawn from extent data collected during some surveys. Not all surveys collected meadow extent data (e.g., Torres Strait lobster surveys). The seagrass meadow layer is a composite of all the spatial polygon data we could access where meadow boundaries were mapped as part of the survey. All spatial layers were compiled into a single spatial layer using the ArcToolbox ‘merge’ function in ArcMap. Where the same meadow was surveyed multiple times as part of a long-term monitoring program, the overlapping polygons were compiled into a single polygon using the ‘merge’ function in ArcMap. Because meadows surveyed more than once were merged, there were some cases where adjacent polygons overlap each other.

Meadow Data Includes:
1. Temporal survey details – Survey month and year, or a list of survey dates for meadows repeatedly sampled;
2. Survey methods;
3. Meadow persistence – Classified into three categories:
a. Unknown – Unknown persistence as the meadow was surveyed less than five times;
b. Enduring – Seagrass is present in the meadow ≥90% of the surveys;
c. Transitory – Seagrass is present in the meadow <90% of the surveys;
4. Meadow depth – Classified into three categories:
a. Intertidal – Meadow was mapped on an exposed bank during low tide, e.g. Karumba monitoring meadow;
b. Subtidal – Meadow remains completely submerged during spring low tides, e.g. Dugong Sanctuary meadow;
c. Intertidal-Subtidal – Meadow includes sections that expose during low tide and sections that remain completely submerged, e.g. meadows adjacent to the Thursday Island shipping channel;
5. Dominant species of the meadow based on the most recent survey;
6. Presence or absence of individual seagrass species in a meadow;
7. Meadow density categories – Seagrass meadows were classified as light, moderate, dense, variable or unknown based on the consistency of mean above-ground biomass of the dominant species among all surveys, or percent cover of all species combined (see Table 2 in Carter et al. 2022). For example, a Halophila ovalis dominated meadow would be classed as “light” if the mean meadow biomass was always <1 gram dry weight m-2 (g DW m-2) among years, “variable” if mean meadow biomass ranged from <1 - >5 g DW m-2, and “dense” if mean meadow biomass was always >5 g DW m-2 among years. For meadows with density assessments based on both percent cover (generally from older surveys) and biomass, we assessed density categories based on the biomass data as this made the assessment comparable to a greater number of meadows, and comparable to the most recent data. Meadows with only one year of data were assigned a density category based on that year but no assessment of variability could be made and these are classified as “unknown”;
8. The minimum and maximum annual mean above-ground biomass measured in g DW m-2 (+ standard error if available) for each meadow is included for meadows with >1 year of biomass data. For meadows that were only surveyed once the mean meadow biomass (+ standard error if available) is presented as the minimum and maximum biomass of the meadow. “-9999” represents meadows where no above-ground biomass data was collected.;
9. The minimum and maximum annual mean percent cover is included for each meadow with >1 year of percent cover data. For meadows that were only surveyed once the mean meadow percent cover is presented as the minimum and maximum percent cover of the meadow. Older surveys (e.g., 1986 Gulf of Carpentaria surveys) used percent cover rather than biomass. For some surveys percent cover was estimated as discrete categories or ‘data binning’ (e.g., <10% - >50%). “-9999” represents meadows where no percent cover data was collected;
10. Meadow area survey details – The minimum, maximum and total area (hectares; ha) for each meadow:
a. Total area - Total area of each meadow was estimated in the GDA 1994 Geoscience Australia Lambert projection using the ‘calculate geometry’ function in ArcMap. For meadows that were mapped multiple times, meadow area represents the merged maximum extent for all surveys.
11. Minimum and maximum area – For meadows surveyed more than once the minimum and maximum annual area of the meadow was reported. For meadows that were only surveyed once the meadow area is presented as the minimum and maximum area of the meadow. Where possible, we retained area data reported in the original shapefiles (and calculated using original projections). Where area data did not exist in original shapefiles (e.g., 1986 Gulf of Carpentaria surveys), we calculated area using the ‘calculate geometry’ function in ArcMap in the GDA 1994 Geoscience Australia Lambert projection; Data custodians.

Spatial Limits:
Data was limited to that collected in the Gulf of Carpentaria between Cape Arnhem (Northern Territory) and Cape York (Queensland). Torres Strait data was restricted to north of Queensland’s Great Barrier Reef World Heritage Area boundary, and includes data collected along the Papua New Guinea coastline.

Taxonomy:
Seagrass taxonomic revision over the last couple of decades has resulted in the revision and reclassification of some tropical species. For example, Zostera capricorni has been reclassified as Zostera muelleri subsp. capricorni, Halophila minor a synonym of Halophila ovalis, and Halodule pinifolia a synonym of Halodule uninervis. Field surveys have at times grouped species that are difficult to distinguish in the field. To address these issues, we amalgamated some species into complexes: Halophila minor and Halophila ovalis are included as Halophila ovalis complex. Zostera muelleri subsp. capricorni has been abbreviated to Zostera capricorni throughout for simplicity.

Base Map:
The base map used in the preview maps is courtesy ESRI 2022.

Data Sets:
Data was limited to that collected in the Gulf of Carpentaria between Cape Arnhem (Northern Territory) and Cape York (Queensland). Torres Strait data was restricted to north of Queensland’s Great Barrier Reef World Heritage Area boundary, and includes data collected along the Papua New Guinea coastline.

Further information in the data sets included in this synthesis can be found in this report:
Carter A, McKenna S, Rasheed M, Taylor H, van de Wetering C, Chartrand K, Reason C, Collier C, Shepherd L, Mellors J, McKenzie L, Roelofs A, Smit N, Groom R, Barrett D, Evans S, Pitcher R, Murphy N, Duke NC, Carlisle M, David M, Lui S, Torres Strait Indigenous Rangers (led by Pearson L, Laza T, Bon A), and Coles RG (2022). Four Decades of Seagrass Spatial Data from Torres Strait and Gulf of Carpentaria. Report to the National Environmental Science Program. Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University.

Limitations of the Data:
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 40 years. This layer represents the most reliable interpretation of that early data.

Not all surveys collected meadow data, including Torres Strait lobster and beche de mer surveys and Torres Strait intertidal transect monitoring collected only site data. Because of this, the meadow layer represents an underestimate of seagrass extent, particularly in deeper subtidal waters. The meadow layer should be used in conjunction with the site layer to determine where meadows have been mapped, and where seagrass surveys have occurred but no seagrass has been found.

See Table 1 and Data age, Limitations and Variability section in Carter et al. (2022).

Format of the data:
This dataset consists of a point shapefile and polygon shapefile with a projected coordinate system of GDA 1994 Geoscience Australia Lambert:
1. Torres Strait and Gulf of Carpentaria seagrass survey sites, 1983-2022 - The point shapefile has been saved as a layer package (TS_GOC_sites_1983_2022.lpk) with symbology representing seagrass presence/absence.
2. Torres Strait and Gulf of Carpentaria seagrass meadows, 1984-2022 - The polygon shapefile has been saved as a layer package (TS_GOC_meadows_1984_2022.lpk). This layer was converted to a geopackage by eAtlas with minor modifications.

Data Dictionary:

Torres Strait and Gulf of Carpentaria seagrass survey sites, 1983-2022 (point data)

- Site (numeric) - Unique identifier representing a single sample site
- Month (text) – Survey month
- Year (numeric) – Survey year
- Survey (text) – Name of survey location
- Latitude (numeric) – Site location in decimal degrees south
- Longitude (numeric) – Site location in decimal degrees east
- Depth_MSL (numeric) – depth below mean sea level in metres
- Custodian (text) – Custodian/owner of the data set
- Substrate (text) – Dominant sediment category
- SG_present (numeric) – Absence (0) or Presence (1) of seagrass
- SG_Species (numeric) – number of species present at the site [between 0 – 8, or -9999 where number of species were not recorded
- CR_PA (numeric) – Absence (0) or Presence (1) of Cymodocea rotundata or -9999 where species was not recorded
- CS_PA (numeric) – Absence (0) or Presence (1) of Cymodocea serrulata or -9999 where species was not recorded
- EA_PA (numeric) – Absence (0) or Presence (1) of Enhalus acoroides or -9999 where species was not recorded
- HC_PA (numeric) – Absence (0) or Presence (1) of Halophila capricorni or -9999 where species was not recorded
- HD_PA (numeric) – Absence (0) or Presence (1) of Halophila decipiens or -9999 where species was not recorded
- HO_PA (numeric) – Absence (0) or Presence (1) of Halophila ovalis or -9999 where species was not recorded
- HS_PA (numeric) – Absence (0) or Presence (1) of Halophila spinulosa or -9999 where species was not recorded
- HT_PA (numeric) – Absence (0) or Presence (1) of Halophila tricostata or -9999 where species was not recorded
- HU_PA (numeric) – Absence (0) or Presence (1) of Halodule uninervis or -9999 where species was not recorded
- SI_PA (numeric) – Absence (0) or Presence (1) of Syringodium isoetifolium or -9999 where species was not recorded
- TC_PA (numeric) – Absence (0) or Presence (1) of Thalassodendron ciliatum or -9999 where species was not recorded
- TH_PA (numeric) – Absence (0) or Presence (1) of Thalassia hemprichii or -9999 where species was not recorded
- ZC_PA (numeric) – Absence (0) or Presence (1) of Zostera muelleri subsp. Capricorni or -9999 where species was not recorded
- Comments (text) – Any comments for that site
Method (text) – e.g. helicopter, walking, hovercraft, boat-based including camera, free diving, scuba diving, van Veen grab, sled net

Torres Strait and Gulf of Carpentaria seagrass meadows, 1984-2022 (polygon data)

- ID (numeric) - Unique identifier representing a single meadow
- SURVEY_NAME (text) – Name of survey location
- SURVEY_DATE (text) – A list of survey date(s) for meadows repeatedly sampled; month and year
- PERSISTENCE (text) – Meadow form on three categories: enduring, transitory, unknown
- DEPTH (text) – Classified into three categories (intertidal, subtidal, intertidal-subtidal)
- DENSITY (text) – Meadow density categories (light, moderate, dense, variable, unknown)
- AREA (text) - Area of the composite meadow in a given location in hectares, represents merged maximum extent
- SURVEY METHOD (text) – e.g., helicopter, walking, hovercraft, boat-based including camera, free diving, scuba diving, van Veen grab, sled net
- COMMENTS (text) – Any comments for that site
- CUSTODIAN (text) – Custodian/owner of the data set
- NO_SURVEYS (numeric) – Number of times meadow has been surveyed
- DOMINANT_SPP [DOM_SPP] (text) – The dominant species in the meadow
- EA_PA (numeric) – Absence (0) or Presence (1) of Enhalus acoroides
- TC_PA (numeric) – Absence (0) or Presence (1) of Thalassodendron ciliatum
- TH_PA (numeric) – Absence (0) or Presence (1) of Thalassia hemprichii
- CS_PA (numeric) – Absence (0) or Presence (1) of Cymodocea serrulata
- CR_PA (numeric) – Absence (0) or Presence (1) of Cymodocea rotundata
- ZC_PA (numeric) – Absence (0) or Presence (1) of Zostera muelleri subsp. capricorni
- HU_PA (numeric) – Absence (0) or Presence (1) of Halodule uninervis
- SI_PA (numeric) – Absence (0) or Presence (1) of Syringodium isoetifolium
- HS_PA (numeric) – Absence (0) or Presence (1) of Halophila spinulosa
- HT_PA (numeric) – Absence (0) or Presence (1) of Halophila tricostata
- HO_PA (numeric) – Absence (0) or Presence (1) of Halophila ovalis
- HC_PA (numeric) – Absence (0) or Presence (1) of Halophila capricorni
- HD_PA (numeric) – Absence (0) or Presence (1) of Halophila decipiens
- BIO_MIN (numeric) – The minimum mean meadow biomass measured in g DW m-2 for meadows sampled more than once, or -9999 where biomass data not recorded
- BIO_MIN_SE (numeric) – Standard error of the minimum mean meadow biomass measured in g DW m-2, or -9999 where biomass data not recorded
- BIO_MAX (numeric) – The maximum mean meadow biomass measured in g DW m-2 for meadows sampled more than once, or -9999 where biomass data not recorded
- BIO_MAX_SE (numeric) – Standard error of the maximum mean meadow biomass measured in g DW m-2, or -9999 where biomass data not recorded
- PER_CO_MIN (numeric) – The minimum mean meadow percent cover for meadows sampled more than once, or -9999 where percent cover data not recorded
- PER_CO_MAX (numeric) – The maximum meadow percent cover for meadows sampled more than once, or -9999 where percent cover data not recorded
- AREA_MIN (numeric) – The minimum area for meadows sampled more than once
- AREA_MAX (numeric) – The maximum area for meadows sampled more than once

Report:
A detailed report describing this project is available:
Carter A, McKenna S, Rasheed M, Taylor H, van de Wetering C, Chartrand K, Reason C, Collier C, Shepherd L, Mellors J, McKenzie L, Roelofs A, Smit N, Groom R, Barrett D, Evans S, Pitcher R, Murphy N, Duke NC, Carlisle M, David M, Lui S, Torres Strait Indigenous Rangers (led by Whap T, Pearson L, Laza T, Bon A), and Coles RG (2022). Four Decades of Seagrass Spatial Data from Torres Strait and Gulf of Carpentaria. Report to the National Environmental Science Program. Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University. https://www.nespmarinecoastal.edu.au/technical-reports-2/

eAtlas Processing:
The original data was provided as ArcGIS Layer Packages and for meadows an additional csv file. The Site lpk was converted to Shapefile format with no changes to the underlying data. The meadow layer was converted to a Geopackage to allow additional survey dates (as provided on CSV) to be represented in the data. Other minor formatting modifications to the survey date column data were performed.

This dataset is filed in the eAtlas enduring data repository at: data\custodian\2021-2022-NESP-MaC-1\1.13_Torres-Strait-GoC-seagrass