Assessment of Posidonia australis transplant survival at 3, 8, 12, 18, and 26 months (August transplant); and 3, 8, 12, 18, 26 and 30 months (April transplant), after planting at Middle Bluff, and Dubaut Point, Shark Bay.

Genomic sampling locations and meadow indices for ribbon weed (Posidonia australis) and wire weed (Amphibolis antarctica) in Shark Bay (Gathaagudu)

Growth (shoot count) of Amphibolis antarctica and Posidonia australis following transplant to Middle Bluff and Dubaut Point, Shark Bay. Plants were transplanted by the Malgana people with assistance from UWA staff then assessed for shoot counts after 8 months.

Total organic carbon (TOC) sediment stocks as a CO2 mitigation service require exclusion of allochthonous black (BC) and particulate inorganic carbon corrected for water–atmospheric equilibrium (PICeq). For the first time, we address this bias for a temperate salt marsh and a coastal tropical seagrass in BC hotspots that represent two different blue carbon ecosystems of Malaysia and Australia. Seagrass TOC stocks were similar to the salt marshes with soil depths < 1 m (59.3 ± 11.3 and 74.9 ± 18.9 MgC ha-1, CI 95% respectively). Both ecosystems showed larger BC constraints than their pristine counterparts did. However, the seagrass meadows’ mitigation services were largely constrained by both higher BC/TOC and PICeq/TOC fractions (38.0% ± 6.6% and 43.4% ± 5.9%, CI 95%) and salt marshes around a third (22% ± 10.2% and 6.0% ± 3.1% CI 95%). The results provide useful data from underrepresented regions, and, reiterates the need to consider both BC and PIC for more reliable blue carbon mitigation assessments.

This record provides an overview of the NESP Marine and Coastal Hub Research Plan 2023 project "Exploring the distribution and ecological value of seagrass at the Furneaux Islands, Tasmania". For specific data outputs from this project, please see child records associated with this metadata. -------------------- Seagrass meadows are a dominant marine ecosystem of Tayaritja (the Furneaux Group of Islands) in north-eastern Tasmania. Historical coarse-scale mapping indicated extensive beds of Posidonia, Amphibolis, Heterozostera and Zostera, with the Posidonia and Amphibiolis beds being potentially some of the largest and deepest extents in temperate Australian waters. These habitats provide ecological, social, cultural and economic values, including habitat for fish and for maireener shells used by Pakana people for traditional necklace making. This project worked in partnership with the Tasmanian Aboriginal Centre (TAC) to improve knowledge of seagrass extent, composition, population structure, ecological condition and blue carbon value around Tayaritja. Existing data were collated to guide survey design for mapping, and high-resolution satellite remote sensing was used to map seagrass beds down to a depth of approximately 30 metres, including intertidal lagoon systems associated with the Logan Lagoon Ramsar site. Field surveys, including video observations and rhizome coring, were used to validate satellite-derived maps and collect ecological samples. Outputs from this project include spatial layers of seagrass extent, variability and species composition, classified using the Seamap Australia National Benthic Habitat Classification Scheme. Rhizome samples were used to assess blue carbon storage, genetic connectivity and diversity, population structure, reproductive strategies, and relationships between seagrass, animal and microbial communities in shallow waters. The project developed new standards-based approaches for collecting, analysing, managing and reporting seagrass data, alongside training and guidance for the TAC land and sea management team and Pakana Rangers. The resulting methods and datasets will support Indigenous-led monitoring and management of the proposed Tayaritja Sea Country Indigenous Protected Area (IPA), and improve understanding of wetland values relevant to Ramsar reporting and future blue carbon opportunities. Outputs • Seagrass extent and composition map for Furneaux group [dataset] • Seagrass imagery and associated seafloor annotations [dataset] • Final project report [written]