Subtidal habitat of North-West Marra Sea Country, Gulf of Carpentaria, Northern Territory, Australia - 2023 (JCU, Mabunji, CDU)

Full description

This dataset summarises subtidal benthic surveys in North-West Marra Sea Country into 1 GIS shapefile: (1) A point (site) shapefile describes seagrass presence/absence at 63 subtidal sites surveyed by vessel. Methods: The sampling methods used to study, describe and monitor seagrass meadows were developed by TropWATER and tailored to the location and habitat surveyed; these are described in detail in the relevant publications (https://research.jcu.edu.au/tropwater). Geographic Information System (GIS): All survey data were entered into a Geographic Information System (GIS) using ArcGIS 10.8. A GIS layer was created to describe spatial features of the region and point data of seagrass presence and absence in survey area. Site layer: This layer contains information on data collected at assessment sites. This layer includes: 1. Temporal survey details – Survey date; 2. Spatial position - Latitude/longitude; 3. Survey location; 4. Seagrass information including presence/absence of seagrass, above-ground biomass (total and for each species), percent cover of seagrass at each site; 5. Benthic macro-invertebrate information including the percent cover of hard coral, soft coral, sponges and other benthic macro invertebrates (e.g. ascidian, clam) at a site; 6. Algae information including percent cover of algae functional groups at a site; 7. Open substrate – the percent cover of the site that had no flora or habitat forming benthic invertebrates present; 8. Dominant sediment type - Sediment type based on grain size visual assessment or deck descriptions, listed in order of dominance; 9. Survey method and vessel; 10. Relevant comments and presence/absence of megafauna and animals of interest (dugong, turtle, dolphin); and 11. Data custodians. Base map: The base map used is courtesy ESRI 2025. Limitations of the data: Recordings of dugong, turtle, and dolphin were opportunistic sightings and recorded if nearby a survey site. This presence/absence data was not collected as part of a formal structured survey of these animals and should therefore be used with caution. Format of the data: This dataset consists of 1 shapefile: 1. GoC_JCU_NorthWest-Marra-Sea-Country_2023_Subtidal-Sites.shp - Symbology representing seagrass presence/absence at each survey site. Data Dictionary: North-West Marra Sea Country subtidal sites 2023 (point data): - SITE (numeric) - Unique identifier representing a single sample site. - SURVEY_DAT (numeric) – survey date (day/month/year). - MONTH (text) – survey month. - YEAR (numeric) – survey year. - SURVEY_NAM (text) – Name of survey location. - LOCATION (text) – Name of survey location. - LATITUDE (numeric) – Site location in decimal degrees south. - LONGITUDE (numeric) – Site location in decimal degrees east. - TIME (numeric) – sample time (24 hours; GMT +9:30) (NT time - subtidal sites only). - DEPTH_MSL (numeric) – depth below mean sea level (metres) for subtidal sites. Intertidal sites depth recorded as 0. - TIDAL (text) – identifying if the site was in an intertidal or subtidal location - SUBSTRATE (text) – tags identifying the types of substrates at the sample site. Possible tags are Mud, Sand, Coarse Sand, Silt, Shell, Rock, Reef, Rubble and various combinations. Listed in order from most dominant substrate to least dominant. - SEAGRASS_P (numeric) – Absence (0) or Presence (1) of seagrass. - SEAGRASS_C (numeric) - Estimated % of seagrass cover at sample site. - SEAGRASS_B (numeric) - Estimated total biomass per square metre for sample site calculated from the mean of three replicate quadrats. Unit is gdw m^-2. - SEAGRASS_S (numeric) – standard error of biomass at sample site calculated from the three replicate quadrats used to estimate biomass at a sample site. Unit is gdw m^-2. - EXCLUDE_FR (numeric) – Include (0) or Exclude (1). Any site identified that needs to be excluded from contributing to the calculation of mean meadow biomass, e.g. where a visual estimate of biomass could not be optioned (i.e. no visibility at the site, only a van Veen sediment grab was used at the site). - HU_BIO (numeric) – Estimated biomass of Halodule uninervis at the site. Unit is gdw m^-2. - HD_BIO (numeric) – Estimated biomass of Halophila decipiens at the site. Unit is gdw m^-2. - EA_BIO (numeric) – Estimated biomass of Enhalus acoroides at the site. Unit is gdw m^-2. - TC_BIO (numeric) – Estimated biomass of Thalassodendron ciliatum at the site. Unit is gdw m^-2. - TH_BIO (numeric) – Estimated biomass of Thalassia hemprichii at the site. Unit is gdw m^-2. - CS_BIO (numeric) – Estimated biomass of Cymodocea serrulata at the site. Unit is gdw m^-2. - CR_BIO (numeric) – Estimated biomass of Cymodocea rotundata at the site. Unit is gdw m^-2. - ZC_BIO (numeric) – Estimated biomass of Zostera muelleri subsp. capricorni at the site. Unit is gdw m^-2. - SI_BIO (numeric) – Estimated biomass of Syringodium isoetifolium at the site. Unit is gdw m^-2. - HS_BIO (numeric) – Estimated biomass of Halophila spinulosa at the site. Unit is gdw m^-2. - HT_BIO (numeric) – Estimated biomass of Halophila tricostata at the site. Unit is gdw m^-2. - HO_BIO (numeric) – Estimated biomass of Halophila ovalis at the site. Unit is gdw m^-2. - ALGAE_TURF (numeric) – (Turf mat algae % contribution to algae cover). Algae that forms a dense mat on the substrate. - ALGAE_MACR (numeric) – (Erect macrophyte algae % contribution to algae cover). Macrophytic algae with an erect growth form and high level of cellular differentiation, e.g. Sargassum, Caulerpa and Galaxaura species. - ALGAE_ENCR (numeric) – (Encrusting algae % contribution to algae cover). Algae that grows in sheet-like form attached to the substrate or benthos, e.g. coralline algae. - ALGAE_CALC (numeric) – (Erect calcareous algae % contribution to algae cover). Algae with erect growth form and high level of cellular differentiation containing calcified segments, e.g. Halimeda species. - ALGAE_FILA (numeric) – (Filamentous algae % contribution to algae cover). Thin, thread-like algae with little cellular differentiation. - HARD_CORAL (numeric) – (Hard coral %). All scleractinian corals including massive, branching, tabular, digitate and mushroom. - SOFT_CORAL (numeric) – (Soft coral %). All alcyonarian corals, i.e. corals lacking a hard limestone skeleton. - SPONGES (numeric) – (Sponge %). - OTHER_BMI (numeric) – Any other benthic macro-invertebrates identified, e.g. oysters, ascidians, clams. Other benthic macro-invertebrates are listed in the “comments” attribute for intertidal and shallow subtidal camera drops, and listed as percent cover in the deepwater GIS. - OPEN_SUBST (numeric) – Open substrate, no seagrass, algae or benthic macro-invertebrates at site. *Note: SEAGRASS_C + ALGAE_TURF + ALGAE_MACR + ALGAE_ENCR + ALGAE_CALC + ALGAE_FILA + HARD_CORAL + SOFT_CORAL + SPONGES + OTHER_BMI + OPEN_SUBST = 100% of benthic cover - DUGONG (numeric) - Absence (0) or Presence (1) of dugong/s near site. - TURTLE (numeric) - Absence (0) or Presence (1) of turtle/s near site. - DOLPHIN (numeric) - Absence (0) or Presence (1) of dolphin/s near site. - DFTS_PRESE (numeric) - Absence (0) or Presence (1) of dugong feeding trails at site. Only clearly visible and therefore assessed at intertidal sites. Subtidal sites not assessed for DFTs coded as -999 - SURVEY_MET (text) – e.g. helicopter, walking, hovercraft, boat-based including camera, free diving, scuba diving, van Veen grab, sled net. - VESSEL (text) – Vessel name (if known). - COMMENTS (text) – Any comments for that site. - CUSTODIAN (text) – Custodian/owner of the data set. - UPDATED (text) - The date the shapefile was last updated. - AUTHOR (text) – Creator of GIS from the data set. References: Carter A, Whitman K, Collier C, Smith T, Barrett D, Barrett E, Evans S, Kerr R, Wilkins S, Kellett D, Groom R (2025) Subtidal Habitat of North-West Marra Sea Country. Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) Report Number 25/16, James Cook University, Cairns, 22 pp. eAtlas Processing: The following shapefile attributes were renamed to match the data dictionary and similar datasets. No modifications to the underlying data were performed. - GoC_JCU_NorthWest-Marra-Sea-Country_2023_Subtidal-Sites.shp: SG_PRESENT -> SEAGRASS_P; OPEN -> OPEN_SUBST; OTHER -> OTHER_BMI Location of the data: This dataset is filed in the eAtlas enduring data repository at: data\2020-2029-other\GoC_JCU_Marra-Sea-Country-Monitoring_2023

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Maintenance and Update Frequency: asNeeded

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Purpose
This project is a partnership between the li-Anthawirriyarra rangers, Marra Traditional Owners, Charles Darwin University (Northern Institute) and James Cook University (TropWATER), to map the subtidal habitats of North-West Marra Sea Country in the Gulf of Carpentaria. Benthic habitat maps of North-West Marra Sea Country were produced, with a focus on seagrass. This project was funded by the Northern Territory Parks and Wildlife Commission.