Subtidal habitats of South East Arnhem Land Sea Country Indigenous Protected Area 2023 (NESP MaC 3.5, JCU, CDU, ECU)

Full description

This dataset summarises a subtidal benthic survey of South East Arnhem Land’s Sea Country Indigenous Protected Area between Nyinpinty Point to Ranjiyirrijt Point, Gulf of Carpentaria, in 2023. Data is presented as 3 GIS layers: (1) A point (site) shapefile that describes (a) seagrass presence/absence, (b) seagrass species composition, (c) algae cover and (d) benthic macro-invertebrate cover at 151 sites surveyed by vessel. (2) A polygon (meadow) shapefile that describes seagrass features for 8 individual meadows. (3) An interpolation raster depicting variation in seagrass biomass within meadows. Carter A, Settli E, Nunggarrgalu C, Hall D, Pomery L, Ponto S, Harvey-Aziz S, Thompson R, Wurramara P, Roy J, Daniels C, Hall D, Collier C, Gordon A, McMahon K, Webster C, Groom R (2025) Marine Habitats of South East Arnhem Land Indigenous Protected Area: Ranjiyirrijt to Nyinpinti Point. Report to the Reef and Rainforest Research Centre, Cairns, Queensland. Data access: Public access to this dataset is restricted. Please refer to the Data Access Control Plan (https://nextcloud.eatlas.org.au/apps/sharealias/a/GoC_NESP-MaC-3-5_JCU_Subtidal-habitats-SEAL-2023) for more information. Methods: The methods used to study, describe and monitor seagrass meadows were developed by TropWATER JCU and tailored to the location and habitat surveyed; these are described in detail in a number of previous reports (https://www.tropwater.com/reports-and-publications). Geographic Information System (GIS): All survey data were entered into a Geographic Information System (GIS) using ArcGIS Pro 3.4. Three spatial layers were created to describe spatial features of the region and point data of seagrass presence and absence in survey area. SEAL Habitat Sites 2023 layer: This layer contains information on data collected at habitat assessment sites, and 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 and whether individual species were present/absent at a site; 5. Benthic macro-invertebrate information including the percent cover of hard coral, soft coral, sponges and other benthic macro invertebrates (e.g. ascidian) at a site; 6. Algae information including percent cover of algae at a site and percent contribution of algae functional groups to algae cover 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. 9. Survey method and vessel; 10. Data custodians. SEAL Seagrass Meadows 2023 layer: This layer contains summary information for all sites within the meadows (polygons). It was created using intertidal seagrass meadow boundaries mapped in 2022, satellite imagery and 2023 seagrass presence/absence site data in ArcGIS Pro. The layer includes: 1. Temporal survey details – Survey month and year as individual columns and the survey date; 2. Spatial survey details – Survey location, meadow identification number that identifies survey site groupings; 3. Survey method and vessel; 4. Meadow depth – Intertidal/subtidal; 5. Species presence – A list of the seagrass species in the meadow; 6. Density – Seagrass meadows were classified as light, moderate, dense based on the mean biomass of the dominant species within the meadow. For example, a Halodule uninervis dominated meadow would be classed as “light” if the mean meadow biomass was <1 grams dry weight m^-2 (g DW m^-2), and “dense” if mean meadow biomass was >4 g DW m^-2. 7. Community – Seagrass meadows were classified into community types according to seagrass species composition within each meadow. Species composition was based on the percent each species’ biomass contributed to mean meadow biomass. A standard nomenclature system was used to categorize each meadow. 8. Mean meadow biomass measured in g DW m^-2 (+ standard error if available); 9. Meadow area (hectares; ha) of each meadow was calculated in the GDA2020 MGA Zone 53 projection using the ‘calculate geometry’ function in ArcGIS Pro. 10. Comments; 11. Data custodians. SEAL Biomass Interpolation 2023 raster: An inverse distance weighted (IDW) interpolation was applied to seagrass site data to describe spatial variation in seagrass biomass within seagrass meadows. The interpolation was produced using ArcGIS Pro 3.4. Base map: The base map used is courtesy ESRI 2025. Format of the data: This dataset consists of 3 layers with a spatial reference of GDA2020 MGA Zone 53: 1. SEAL Seagrass Meadows 2023 – polygon shapefile 2. SEAL Biomass Interpolation 2023 - raster 3. SEAL Habitat Sites 2023 – point shapefile Data Dictionary: SEAL Habitat Sites 2023 (point data): - SITE (numeric) - Unique identifier representing a single sample site. - TIME (numeric) – Sample time (24 hours; GMT +9:30) (NT time). - SURVEY_DAT (numeric) – Survey date (day/month/year). - MONTH (text) – Survey month. - YEAR (numeric) – Survey year. - SURVEY_NAM (text) – Name of survey. - LOCATION (text) – Survey location, e.g. island, marine park zone, sea country boundary, etc. - LATITUDE (numeric) – Site location in decimal degrees south. - LONGITUDE (numeric) – Site location in decimal degrees east. - DEPTH_MSL (numeric) – Depth below mean sea level (- meters). - 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 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_B (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 was not possible (i.e. no visibility at the site, only a van Veen sediment grab was used at the site). - C_ROTUNDAT (numeric) – Estimated biomass of Cymodocea rotundata at the site. Unit is gdw m^-2. - C_SERRULAT (numeric) – Estimated biomass of Cymodocea serrulata at the site. Unit is gdw m^-2. - E_ACOROIDE (numeric) – Estimated biomass of Enhalus acoroides at the site. Unit is gdw m^-2. - H_UNINERIV (numeric) – Estimated biomass of Halodule uninervis at the site. Unit is gdw m^-2. - H_DECIPIEN (numeric) – Estimated biomass of Halophila decipiens at the site. Unit is gdw m^-2. - H_OVALIS (numeric) – Estimated biomass of Halophila ovalis at the site. Unit is gdw m^-2. - H_SPINULOS (numeric) – Estimated biomass of Halophila spinulosa at the site. Unit is gdw m^-2. - H_TRICOSTA (numeric) – Estimated biomass of Halophila tricostata at the site. Unit is gdw m^-2. - S_ISOETIFO (numeric) – Estimated biomass of Syringodium isoetifolium at the site. Unit is gdw m^-2. - T_CILIATUM (numeric) – Estimated biomass of Thalassodendron ciliatum at the site. Unit is gdw m^-2. - T_HEMPRICH (numeric) – Estimated biomass of Thalassia hemprichii at the site. Unit is gdw m^-2. - Z_CAPRICOR (numeric) – Estimated biomass of Zostera muelleri subsp. capricorni at the site. Unit is gdw m^-2. *Note: C_ROTUNDAT + C_SERRULAT + E_ACOROIDE + H_UNINERIVS + H_DECIPIEN + H_OVALIS + H_SPINULOS + H_TRICOSTA + S_ISOETIFO + T_CILIATUM + T_HEMPRICH + Z_CAPRICOR = SEAGRASS_B - TURF_MAT (numeric) – Turf mat algae % contribution to algae cover. Algae that forms a dense mat on the substrate. - ERECT_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. - ENCRUSTING (numeric) – Encrusting algae % contribution to algae cover. Algae that grows in sheet-like form attached to the substrate or benthos, e.g. coralline algae. - ERECT_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. - FILAMENTOU (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) – % cover of any other benthic macro-invertebrates (BMI), e.g. bryozoans, ascidians. Other BMI are listed in the “comments” column. - OPEN_SUBST (numeric) – % cover of bare, open substrate. - METHOD (text) – e.g. helicopter, walking, hovercraft, drone, boat-based including camera, free diving, scuba diving, van Veen grab, sled net. - VESSEL (text) – Vessel name. - COMMENTS (text) – Any comments for that site. - AUTHOR (text) – Creator of GIS from the data set and date of creation. - UPDATED (date) – Date of last update of the spatial layers. - CUSTODIAN (text) – Custodian/owner of the data set. - TIDAL (text) – Subtidal or intertidal. - MEADOW (text) – Seagrass meadow ID codes. *Note: SEAGRASS_C + TUR_MAT + ERECT_MACR + ENCRUSTING + ERECT_CALC + FILAMENTOU + HARD_CORAL + SOFT_CORAL + SPONGE + OTHER_BMI + OPEN_SUBSTRATE = 100% of benthic cover SEAL Seagrass Meadows 2023 (polygon data): - MEADOW_ID (numeric) - Unique identifier representing a single meadow. - MONTH (text) – Survey month. - YEAR (numeric) – Survey year. - SURVEY_DAT (date) – Survey date (day/month/year). - LOCATION (text) – Survey location. - SURVEY_NAM (text) – Survey name. - TYPE (text) - Meadow community type determined according to seagrass species composition within the meadow. - DENSITY (text) – Meadow density categories (light, moderate, dense). - Species (text) - List of seagrass species found within the meadow. Species are recorded as abbreviated species names such as “E. acoroides”. - Biomass (numeric) – Seagrass biomass (gdw m^-2). Mean biomass calculated from all sites (BIO_SITES) within an individual meadow. - SE (numeric) – Standard Error (gdw m^-2) of mean biomass. The error is a calculation of standard error of biomass from all (BIO_SITES) sites within an individual meadow. - Area_ha (numeric) – Meadow area (Ha). Estimated meadow size (unit: hectares). - Tot_Sites (numeric) – Number of survey sites within each meadow. - Bio_Sites (numeric) – Number of survey sites within each meadow that mean biomass was calculated from. May differ from TOT_SITES due to site exclusions where biomass estimates were not made because of low visibility, or seagrass detected using a van Veen grab only. - SURVEY_MET (text) – Survey method, e.g. helicopter, boat, camera, sled, van Veen grab. - Comments (text) – Any relevant comments for that meadow. - Updated (date) – The date the shapefile was last updated. - Author (text) - Creator of the GIS dataset. - CUSTODIAN (text) – Custodian/owner of the data set. SEAL Biomass Interpolation 2023 (raster): - Band 1: Interpolated biomass in gdw m^-2 References: Carter A, Settli E, Nunggarrgalu C, Hall D, Pomery L, Ponto S, Harvey-Aziz S, Thompson R, Wurramara P, Roy J, Daniels C, Hall D, Collier C, Gordon A, McMahon K, Webster C, Groom R (2025) Marine Habitats of South East Arnhem Land Indigenous Protected Area: Ranjiyirrijt to Nyinpinti Point. Report to the Reef and Rainforest Research Centre, Cairns, Queensland. eAtlas Processing: No modifications were made to the data as part of publication. Location of the data: This dataset is filed in the eAtlas enduring data repository at: data\custodian\2023-2026-NESP-MaC-3\3.5_Northern-Australia-seagrass-distribution\data\GoC_NESP-MaC-3-5_JCU_Subtidal-habitats-SEAL-2023

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Maintenance and Update Frequency: asNeeded

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Purpose
Northern Australian seagrass meadows support dugongs, green turtles, fish, prawns and other important species. Understanding their distribution and health now, and over time, is essential so regional planners have information to make the right decisions about community activities and economic development. Unfortunately, for large areas of the coast, data on these important habitats is lacking. Few large-scale surveys have been done, and only a handful of ongoing seagrass monitoring programs exist. Presently, regional planning often proceeds without accurate seagrass information, and therefore, with very minimal understanding of potential effects on these critically important ecosystems. NESP Marine and Coastal Hub Project 3.5 - Partnerships for Seagrass Research and Protection addresses gaps in seagrass knowledge by consolidating existing data, identifying the gaps, producing new data sets, and making data more widely available. The objective of this project was to collaborate with the Traditional Owners, Numbulwar Numburindi and Yugul Mangi Rangers in the South East Arnhem Land (SEAL) Sea Country Indigenous Protected Area to undertake a baseline survey of subtidal marine habitats between Nyinpinty Point and Ranjiyirrijt Point. This was done in partnership with TropWATER James Cook University, Northern Institute Charles Darwin University, and Edith Cowen university. The survey was undertaken in October 2023 with ranger vessels Bambeiliwarr and Ngarri Larni. The objectives of the survey were to: (1) Map seagrass and other benthic habitat (e.g. algae, coral, sponge gardens). (2) Produce baseline bilingual habitat maps for the region; (3) Produce a report and spatial data for use by Numbulwar Numburindi rangers, Yugul Mangi rangers, Northern Land Council, South East Arnhem Land Traditional Owners, and government in decision-making in local resource use.