Report cards that are designed to monitor environmental trends have the potential to provide a powerful communication tool because they are easy to understand and accessible to the general public, scientists, managers and policy makers. Given this functionality, they are increasingly popular in marine ecosystem reporting. We describe a report card method for seagrass that incorporates spatial and temporal variability in three metrics—meadow area, species and biomass—developed using long-term (greater than 10 years) monitoring data. This framework summarises large amounts of spatially and temporally complex data to give a numeric score that provides reliable comparisons of seagrass condition in both persistent and naturally variable meadows. We provide an example of how this is applied to seagrass meadows in an industrial port in the Great Barrier Reef World Heritage Area of north-eastern Australia.

Vegetated coastal ecosystems, in particular mangroves, tidal marshes and seagrasses are highly efficient at sequestering and storing carbon, making them valuable assets for climate change mitigation and adaptation. The state of Queensland, in northeastern Australia, contains almost half of the total area of these blue carbon ecosystems in the country, yet there are few detailed regional or state-wide assessments of their total sedimentary organic carbon (SOC) stocks. We compiled existing SOC data and used boosted regression tree models to evaluate the influence of environmental variables in explaining the variability in SOC stocks, and to produce spatially explicit blue carbon estimates. The final models explained 75 % (for mangroves and tidal marshes) and 65 % (for seagrasses) of the variability in SOC stocks. Total SOC stocks in the state of Queensland were estimated at 569 +/- 98 Tg C (173 +/- 32 Tg C, 232 +/- 50 Tg C, and 164 +/- 16 Tg C from mangroves, tidal marshes and seagrasses, respectively). Regional predictions for each of Queensland's eleven Natural Resource Management regions revealed that 60 % of the state's SOC stocks occurred within three regions (Cape York, Torres Strait and Southern Gulf Natural Resource Management regions) due to a combination of high values of SOC stocks and large areas of coastal wetlands. Protected areas in Queensland play an important role in conserving SOC assets in Queensland's coastal wetlands. For example, similar to 19 Tg C within terrestrial protected areas, similar to 27 Tg C within marine protected areas and similar to 40 Tg C within areas of matters of State Environmental Significance. Using multi-decadal (1987-2020) mapped distributions of mangroves in Queensland; we found that mangrove area increased by approximately 30,000 ha from 1987 to 2020, which led to temporal fluctuations in mangrove plant and SOC stocks. We estimated that plant stocks decreased from similar to 45 Tg C in 1987 to similar to 34.2 Tg C in 2020, while SOC stocks remained relatively constant from similar to 107.9 Tg C in 1987 to 108.0 Tg C in 2020. Considering the level of current protection, emissions from mangrove deforestation are potentially very low; therefore, representing minor opportunities for mangrove blue carbon projects in the region. Our study provides much needed information on current trends in carbon stocks and their conservation in Queensland's coastal wetlands, while also contributing to guide future management actions, including blue carbon restoration projects.

Australia's Great Barrier Reef (GBR) catchments include some of the world's most intact coastal wetlands comprising diverse mangrove, seagrass and tidal marsh ecosystems. Although these ecosystems are highly efficient at storing carbon in marine sediments, their soil organic carbon (SOC) stocks and the potential changes resulting from climate impacts, including sea level rise are not well understood. For the first time, we estimated SOC stocks and their drivers within the range of coastal wetlands of GBR catchments using boosted regression trees (i.e. a machine learning approach and ensemble method for modelling the relationship between response and explanatory variables) and identified the potential changes in future stocks due to sea level rise. We found levels of SOC stocks of mangrove and seagrass meadows have different drivers, with climatic variables such as temperature, rainfall and solar radiation, showing significant contributions in accounting for variation in SOC stocks in mangroves. In contrast, soil type accounted for most of the variability in seagrass meadows. Total SOC stock in the GBR catchments, including mangroves, seagrass meadows and tidal marshes, is approximately 137 Tg C, which represents 9%–13% of Australia's total SOC stock while encompassing only 4%–6% of the total extent of Australian coastal wetlands. In a global context, this could represent 0.5%–1.4% of global SOC stock. Our study suggests that landward migration due to projected sea level rise has the potential to enhance carbon accumulation with total carbon gains between 0.16 and 0.46 Tg C and provides an opportunity for future restoration to enhance blue carbon.

Seagrass meadows are considered important natural carbon sinks due to their capacity to store organic carbon (Corg) in sediments. However, the spatial heterogeneity of carbon storage in seagrass sediments needs to be better understood to improve accuracy of Blue Carbon assessments, particularly when strong gradients are present. We performed an intensive coring study within a sub-tropical estuary to assess the spatial variability in sedimentary Corg associated with seagrasses, and to identify the key factors promoting this variability. We found a strong spatial pattern within the estuary, from 52.16 mg Corg cm−3 in seagrass meadows in the upper parts, declining to 1.06 mg Corg cm−3 in seagrass meadows at the estuary mouth, despite a general gradient of increasing seagrass cover and seagrass habitat extent in the opposite direction. The sedimentary Corg underneath seagrass meadows came principally from allochthonous (non-seagrass) sources (~70–90 %), while the contribution of seagrasses was low (~10–30 %) throughout the entire estuary. Our results showed that Corg stored in sediments of seagrass meadows can be highly variable within an estuary, attributed largely to accumulation of fine sediments and inputs of allochthonous sources. Local features and the existence of spatial gradients must be considered in Blue Carbon estimates in coastal ecosystems.

Seagrass condition was assessed for 14 monitoring meadows across six Gladstone Healthy Harbour Partnership (GHHP) reporting zones in November 2017 (GHHP 2018 reporting year). Seagrass condition in the Gladstone Harbour region remained poor (D, 0.40) in the 2018 reporting year. Survey results were mixed for individual meadows and zones. The overall score for each meadow is the lowest of the three indicator scores*. Biomass determined the overall meadow scores in seven monitoring meadows, species composition in six meadows, and area in one meadow. Seagrass condition improved in South Trees Inlet Zone (good to very good), at the Passage Island meadows (good to very good) and the meadow immediately north of Fishermans Landing (very poor to poor) in the Western Basin Zone, and at Pelican Banks (very poor to poor) in the Mid Harbour Zone. Seagrass condition declined in the Western Basin Zone (satisfactory to poor) with declines at the two meadows immediately south of Fishermans Landing (satisfactory to poor, and poor to very poor) and one meadow at Wiggins Island (good to poor). Seagrass condition also declined in The Narrows Zone (satisfactory to poor) and at one meadow in Rodds Bay Zone (poor to very poor). Elsewhere seagrass condition remained the same as the previous year. Gains in biomass and an increase in the proportion of the dominant species Z. muelleri subsp. capricorni at the Pelican Banks meadow—the largest and most stable seagrass meadow in the Gladstone region—are encouraging. The meadow is now in poor condition (an improvement from very poor in the 2017 reporting year), however all three indicators remain below the historical baseline. Environmental conditions influence seagrass condition in Gladstone. Years where >50% of meadows were assigned an overall meadow condition of poor or very poor either correspond with (2010-2016) or directly follow (2004) periods of above average rainfall and river flow in the region. Above average rainfall and riverflow events in March 2017 (associated with Tropical Cyclone Debbie) and October 2017 are likely to have inhibited any substantial seagrass recovery. There was very little seagrass recovery at the Gladstone Harbour scale from the previous year. Resilience of seagrasses to further natural or anthropogenic impacts in the Gladstone Harbour region is likely to be low. This report is presented in two parts. Part 1 summarises report card results for the annual survey. Part 2 is an accompanying technical report that details methods, analysis, results and interpretation.

Marine environmental report cards are an increasingly popular tool to communicate scientific results to stakeholders and communities. The challenge in developing a report card for complex marine habitats is establishing appropriate indicators to evaluate habitat condition. We developed an approach to report on seagrass condition as part of a broader report card on the environmental, social, cultural and economic health of Gladstone Harbour, which contains one of Australia's largest multi-commodity ports located in the Great Barrier Reef World Heritage Area. The process used expert opinion to determine the best indicators of seagrass condition (above-ground biomass, meadow area, species composition), trialled four approaches to determine a baseline condition of each indicator, and defined five condition categories (very good to very poor) to grade each seagrass meadow relative to a baseline. Threshold levels for each condition category were determined based on the historical variability of each indicator in a meadow. The report card approach allowed for the presentation of a large amount of spatial information, including the location, condition, and the justification for each meadow's grade to be presented on a single map. This allows for rapid comparison of seagrass condition across the range of meadows within the port and between years, and also at a broader regional scale. The report card was piloted and refined for the Port of Gladstone over three years and applied to eight other Queensland ports with seagrass monitoring programs in 2015.

• Seagrass condition was assessed for 14 monitoring meadows across 6 Gladstone Healthy Harbour Partnership reporting zones in November 2015 (GHHP 2016 reporting year). • Seagrass condition in the Gladstone Harbour region was poor (D). • Half of the monitoring meadows were assessed as being in poor condition, including all of the monitoring meadows in The Narrows, Mid Harbour and South Trees Inlet Zones. In the Western Basin Zone two meadows were in satisfactory condition, two meadows were in good condition, and two meadows were in poor condition. No meadows were graded as very good for overall meadow condition. • Seagrass was in poor condition in four Gladstone Harbour Zones (The Narrows, Mid Harbour, South Trees Inlet and Rodds Bay); the Inner Harbour Zone was in very poor condition; and the Western Basin Zone was in satisfactory condition. • The overall meadow score for each meadow is the lowest of the three indicator scores. The Narrows, Mid Harbour, South Trees Inlet (lower) and Rodds Bay Zones all received poor scores which were driven by low biomass. Area determined the overall meadow score in the Western Basin Zone in two meadows, species composition in three meadows, and biomass in one meadow. Species composition determined the overall score in the Inner Harbour. • Environmental conditions influence seagrass condition in Gladstone. Years where overall meadow condition was poor/very poor in the majority of meadows either correspond with (2010-2015) or directly follow (2004) years of above average rainfall and discharge in the region, particularly from the Calliope River. These rainfall /river flow peaks are often associated with tropical cyclones. Tropical Cyclone Marcia crossed the coast just north of Gladstone in February 2015, bringing with it short but significant rainfall and flooding from the Fitzroy River (just north of Gladstone) and south to the Upper Brisbane River. • There was no sign of seagrass recovery at the Gladstone Harbour scale from the previous year. Overall seagrass condition improved from very poor to poor in The Narrows; remained stable in the Western Basin (satisfactory) and Rodds Bay (poor); and declined in the Inner Harbour (poor to very poor), Mid Harbour and South Trees inlet (satisfactory to poor). Consecutive years of poor seagrass condition have likely reduced meadow resilience to further impacts. • This report is presented into two parts. Part 1 summarises report card results for the most recent annual survey conducted in November 2015. Part 2 is an accompanying technical report that details methods, analysis, results and interpretation. • Several minor changes to the methods used to assess seagrass condition were applied in the 2016 reporting year. This resulted in minor grade changes in some meadows in some years (e.g. meadow 43 area in 2008). These changes are detailed in Section 2.2 of the report.

Marine environmental report cards are an increasingly popular tool to communicate scientific results to stakeholders and communities. The challenge in developing a report card for complex marine habitats where changes in abundance, cover, distribution and species can occur is establishing appropriate indicators to evaluate habitat condition. We developed an innovative approach for reporting on the condition of seagrasses as part of a broader report card on the environmental, social, cultural and economic health of one of Australia's largest multi-commodity ports located in the Great Barrier Reef World Heritage Area. The process used expert opinion to determine the best indicators of seagrass condition (above-ground biomass, meadow area, species composition), trialled four approaches to determine a baseline condition of each indicator, and defined five condition categories (very good - very poor) to grade each seagrass meadow relative to a baseline. Threshold levels for each condition category were determined based on the historical variability of each indicator in a meadow. The report card approach allowed for the presentation of a large amount of spatial information, including the location, condition, and the reason for each meadow’s grade to be presented within a single map. This allowed not only for rapid comparison of seagrass condition across the range of meadows within the port, but also at a broader regional scale.

[Extract] This report details findings from the second year of a study examining the density of seagrass (Zostera muelleri subsp. capricorni) seeds and their viability in Port Curtis. The project builds on seagrass seed bank assessments that were originally conducted as part of the Western Basin Dredging and Disposal Project (WBDDP). Results of the seed bank density and viability surveys undertaken, to date, have found that: 1. Seeds were present at all sites during all quarterly sampling events, with total seed density relatively high compared with other locations in Queensland where seed banks have been assessed e.g. Moreton Bay, Cairns and Mourilyan Harbour. 2. Seed bank density changed significantly at all sites over the duration of monitoring (2011 to 2016) but trends varied substantially between sites and years. Overall trends in seed bank density tended to mirror trends in peak seagrass density, particularly in the largest seagrass meadow at Pelican Banks. 3. Viable seeds were found in the sediment seed bank at all sites immediately following the end of each growing season (February 2015 and 2016). 4. We suspect that some meadows (Wiggins Island and Rodds Bay) may rely on nearby donor meadows for seed bank replenishment. 5. The average proportion of viable seeds decreased at all sites over the senescent season (from February to May) in 2015, but remained stable (Pelican Banks North) increased (Rodds Bay) or decreased (Wiggins Island) in 2016. 6. On average greater than 70% of all seeds were found at sediment depths >20mm, and for the majority of the sampling period greater than 40% were found at >50mm. This may limit seed bank function if burial depth inhibits germination and/or seedling success. 7. Seasonal trends in total seed bank density were not consistent, with some sites unexpectedly containing significantly higher seed densities following the senescent period (May) compared with densities following replenishment (February), indicating secondary dispersal events or possibly delayed recruitment of seeds to some meadows. Results have also highlighted the complexity of seed bank dynamics. The ongoing sampling planned in 2016 and 2017 will help to further resolve these dynamics but additional investigations would also enhance the understanding of seagrass resilience including studies on: 8. The spatial structure of the seed bank across the broader meadow; 9. Environmental cues for germination and rates of germination and seedling success; and 10. Connectivity between seagrass meadows through seed dispersal within the Port Curtis region.

Coastal seagrass habitats are at risk from a range of anthropogenic activities that modify the natural light environment, including dredging activities associated with coastal and port developments. On Australia's east coast, the tropical seagrass Zostera muelleri ssp. capricorni dominates intertidal mudbanks in sheltered embayments which are also preferred locations for harbours and port facilities. Dredging to establish and maintain shipping channels in these areas can degrade water quality and diminish light conditions that are required for seagrass growth. Based on this potential conflict, we simulated in-situ light attenuation events to measure effects on Z. muelleri ssp. capricorni condition. Semi-annual in situ shading studies conducted over three years were used to quantify the impact of prolonged light reduction on seagrass morphometrics (biomass, percent cover and shoot density). Experimental manipulations were complimented with an assessment of 46 months of light history and concurrent natural seagrass change at the study site in Gladstone Harbour. There was a clear light-dependent effect on seagrass morphometrics during seagrass growing seasons, but no effect during senescent periods. Significant seagrass declines occurred between four and eight weeks after shading during the growing seasons with light maintained in the range of 4 - 5 mol photons m-2 d-1. Sensitivity to shading declined when applied in two-week intervals (fortnightly) rather than continuous over the same period. Field observations were correlated to manipulative experiments to derive an applied threshold of 6 mol photons m-2 d-1 which formed the basis of a reactive light-based management strategy which has been successfully implemented to ensure positive ecological outcomes for seagrass during a large-scale dredging program.

When seagrass meadows are destroyed, what happens to the 'blue carbon' stored within their sediments; does it stay in the ground, or is it released into the atmosphere? Is it possible to manage seagrass ecosystems so that they sequester more blue carbon? With seagrasses now recognised as globally-significant carbon sinks, the answers to these questions have important consequences for nature-based climate change mitigation and adaptation (i.e. 'biosequestration'). We make the case that microbes fundamentally control the fate of sequestered blue carbon within seagrass, and, therefore, management efforts aimed at bolstering blue carbon opportunities within seagrass ecosystems need to target processes that influence (directly or indirectly) microbial remineralisation of blue carbon. New data will be presented showing that blue carbon occurs in hotspots and changes in the geochemistry of seagrass sediments - such as those caused by disturbance - can create hot moments, whereby organic carbon within sediments undergoes rapid and substantial microbial remineralisation. In order to better manage seagrass ecosystems for blue carbon benefits, we outline three recommendations: reducing anthropogenic nutrient inputs, reinstating top-down control of bioturbator populations, and restoring hydrology. These processes are amenable to management control, they promote microbial dormancy and limit microbial priming, and offer ecosystem benefits beyond carbon sequestration.

Key outcomes: This report provides a summary of field and laboratory studies conducted in the course of the development and validation of a set of molecular markers to monitor low light stress in the intertidal seagrass species Zostera muellerissp. capricorni. This is the first molecular study to establish and validate stress markers in an Australian seagrass species. The report also details how these markers can be used as a rapid assessment tool of seagrass health and be applied in active management of activities that impact on the light environment such as dredging. The key outcomes of these studies are: •We have successfully developed a seagrass health molecular tool kit based on real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) technology. This molecular tool kit was established by screening a total of 28 genes and includes a set of 10 reference genes and seven target genes (four early and three late sublethal markers of low light stress). •The molecular tool kit includes a combination of two types of gene responses to low light (up-regulated or down-regulated), which allows fast and robust diagnostics. We confirm plant gene expression returns to control levels once exposure to low light stress is removed. •The seagrass health molecular tool kit has been validated within a set of laboratory-based experiments and an intensive program of field collections, which includes shading studies as well as diel and monthly sampling at permanent transect sites within Port Curtis. •The newly developed field-to-bench workflow for analyzing seagrass health with this molecular tool kit, includes optimized seagrass sample handling in the field, processing, ribonucleic acid (RNA) extraction, cryostorage, bioinformatics and quality control through to the data analysis. The entire workflow has been developed for a fast turn-around time; typically within approx.1 working day upon receipt of field-collected samples. •The bioinformatics pipeline established at the University of Technology Sydney (UTS) to support this project is publicly available as a graphical-driven web-repository (http://144.6.226.79/), which will be used by scientists all over the world to assist in the examination of Z. muelleri transcriptomes. •This novel seagrass health molecular tool kit presents a significant advance in management of dredging operations to protect seagrasses because it: Can detect changes in Z. muelleri within 2 weeks of the onset of low light stress, long before any significant changes occur in physiology / morphology (8weeks); Substantially improves the capacity for reactive management by providing sufficient time for mitigating actions to be taken prior to seagrass loss; Allows assessments of stress to be made anywhere as they are not reliant on an established seagrass monitoring site with a history of known seagrass condition; and Provides a means to easily assess compliance with management conditions and effectiveness of management thresholds

Seagrass meadows are threatened by coastal development and global change. In the face of these pressures, molecular techniques such as reverse transcription quantitative real-time PCR (RT-qPCR) have great potential to improve management of these ecosystems by allowing early detection of chronic stress. In RT-qPCR, the expression levels of target genes are estimated on the basis of reference genes, in order to control for RNA variations. Although determination of suitable reference genes is critical for RT-qPCR studies, reports on the evaluation of reference genes are still absent for the major Australian species Zostera muelleri subsp. capricorni ( Z. muelleri ). Here, we used three different software (geNorm, NormFinder and Bestkeeper) to evaluate ten widely used reference genes according to their expression stability in Z. muelleri exposed to light limitation. We then combined results from different software and used a consensus rank of four best reference genes to validate regulation in Photosystem I reaction center subunit IV B and Heat Stress Transcription factor A- gene expression in Z. muelleri under light limitation. This study provides the first comprehensive list of reference genes in Z. muelleri and demonstrates RT-qPCR as an effective tool to identify early responses to light limitation in seagrass.

Executive Summary: The Seagrass Ecology Group within the Centre for Tropical Water and Aquatic Ecosystem Research at James Cook University (TropWATER) have developed an approach for reporting on the condition of seagrasses in the Gladstone Harbour region for incorporation into the Gladstone Healthy Harbour Partnership (GHHP) 2015 report card. Annual long-term monitoring data collected since 2002 at 14 representative seagrass meadows were used to assess the status of three seagrass indicators (mean above-ground biomass, total meadow area and species composition) relative to baseline conditions at each meadow. We assessed various methods for setting condition thresholds around baseline conditions for meadow biomass, meadow area, and percent composition of species in each meadow. These methods included percentile bands, standard deviations, and percent change above and below the baseline. The 10 year fixed mean (calculated over the period from 2002 – 2012) was considered the most appropriate baseline for which to compare annual indicator values because it incorporates the greatest range of climate conditions known to influence seagrasses in the region for the different assessment periods examined. Several threshold ranges were used, recognising that the biomass, area and species composition in some seagrass meadows are historically stable, while others are relatively variable over time. These differences reflect the changes in species assemblages and growth characteristics at individual monitoring meadows, and spatial variation between meadows growing in marginal inner harbour conditions, versus more favourable mid harbour conditions. The Gladstone Harbour Report Card assesses annual levels for each seagrass condition indicator against baseline conditions to determine a grade from A to E, where A indicates a condition of ‘very good’ and E indicates a condition of 'very poor'. In 2015 a scale was applied to each grade so a score between 0 and 1 could be calculated for each indicator. The lowest of the three indicator scores dictates the overall meadow score and grade. The harbour is divided into 13 reporting zones as part of the GHHP reporting process, 6 of which contain seagrass monitoring meadows. Where multiple monitoring meadows were present within a zone, the mean of the overall meadow scores dictates the overall zone score and grade. Three Gladstone Harbour Zones were determined to be in satisfactory condition (Western Basin, Mid Harbour and South Trees Inlet (lower)), two zones were in poor condition (Inner Harbour and Rodds Bay), and one zone was in very poor condition (The Narrows). The Gladstone Harbour score is the mean of the overall zone scores. An assessment of 14 seagrass monitoring meadows determined that the overall condition of seagrass in the Gladstone Harbour region in 2014 was poor (grade D). The report is presented into two parts. Part 1 presents the report card results for the most recent annual survey conducted in November 2014 (in the GHHP 2014-2015 reporting year). Part 2 is an accompanying technical report detailing the methods for data collection, a comparison of different methods tested to set thresholds, justification for the threshold methods used for the 2015 report card, and a detailed presentation and interpretation of the results.

The Great Barrier Reef World Heritage Area includes one of the world's largest areas of seagrass (35, 000 km2) including 20% of the world's species. Mitigating natural and anthropogenic threats to this biodiverse region requires quantifying the resource for its' effective management. The Queensland Ports Seagrass Monitoring Program conducts long-term seagrass mapping and monitoring in the majority of Queensland's commercial ports. Monitoring focuses on seagrass habitat that is most at risk from the various threats that seagrasses face, providing port managers and regulators with key information to plan and implement port development and maintenance programs that will have minimal impact on seagrasses. The program has been successful in changing coastal development and ports and shipping industry practices, and has improved the ability of managers to protect marine habitats. As a by-product of the program a range of seagrass research projects have been established including developing tools to rapidly assess the health of seagrasses and to implement management triggers and thresholds; investigating seagrass resilience and recovery; quantifying productivity of tropical seagrass systems; and deciphering the role climate plays in shaping tropical seagrass communities. One of the limitations of the program is a sampling bias towards shallow coastal seagrasses within developed regions. This bias creates a problem if using monitoring data for building species and habitat maps. The data produced from the program results in a patchwork distribution of data sets that do not cover the entire ranges of seagrass habitats of the GBR and do not effectively represent relevant spatio-temporal changes making it difficult to produce broad-scale species and habitat maps to aid in management. The Queensland Ports Association is working alongside the Seagrass Ecology Group to try and fill these gaps in knowledge.

Seagrass ecosystems, considered among the most efficient carbon sinks worldwide, encompass a wide variety of spatial configurations in the coastal landscape. Here we evaluated the influence of the spatial configuration of seagrass meadows at small scales (metres) on carbon storage in seagrass sediments. We intensively sampled carbon stocks and other geochemical properties (δ(13)C, particle size, depositional fluxes) across seagrass-sand edges in a Zostera muelleri patchy seagrass landscape. Carbon stocks were significantly higher (ca. 20%) inside seagrass patches than at seagrass-sand edges and bare sediments. Deposition was similar among all positions and most of the carbon was from allochthonous sources. Patch level attributes (e.g. edge distance) represent important determinants of the spatial heterogeneity of carbon stocks within seagrass ecosystems. Our findings indicate that carbon stocks of seagrass areas have likely been overestimated by not considering the influence of meadow landscapes, and have important relevance for the design of seagrass carbon stock assessments.

Seagrass habitats have been the focus of much attention in recent years with increasing recognition of the important role they play in sediment stabilisation, nutrient cycling, and as nursery and feeding grounds for fisheries species and megafauna such as dugong and turtle. With globally developing carbon markets, the role that seagrasses play in sequestering carbon is also becoming more widely recognised. But while shallow water seagrasses have been heavily researched, there are vast areas of seagrass habitat in deeper water which we know very little about. Within the Great Barrier Reef World Heritage Area alone, deepwater (>10m) seagrasses occupy more than 35,000 km2 of the reef lagoon. Predominantly comprised of smaller species, these communities are capable of rapidly turning over their biomass in a matter of days. Given the vast area of these meadows, the potential rate of carbon assimilation is significant. We present preliminary findings from the first two years of an ongoing research program investigating the major drivers of seasonal recruitment and senescence in tropical deepwater seagrass meadows. The program is providing information on seagrass abundance, seed bank status, productivity, benthic irradiance, temperature and spectral quality of light across three geographically distinct locations. Results will inform the development of local management strategies for mitigating impacts from coastal developments where dredging and associated plumes and ship movements threaten the long term survival of deepwater seagrasses.

Global seagrass research and assessment efforts have focused on shallow coastal and estuarine seagrass populations. Comparatively little is known about the dynamics of deep-water (>10m) seagrasses despite evidence they form extensive meadows in some parts of the world and may be highly productive compared with their shallow counterparts. Deep-water seagrasses are subject to a similar range of anthropogenic threats as shallow meadows particularly along the Great Barrier Reef (GBR) in Queensland, where they occur close to major population centres and adjacent to the coast. We examine the dynamics of deep-water seagrass populations in the GBR through a range of research studies including long term (>8 years) assessments of change; impacts of major dredging programs; resilience and recovery from severe tropical storms and; targeted research investigating the drivers, thresholds and tolerances behind seasonal and inter-annual change. Collectively these re- search programs have provided new insight into deep-water seagrass dynamics. Despite considerable inter-annual variability deep-water seagrasses had a regular annual pattern of occurrence at some locations, a low level of resilience to reduced water quality, but a high capacity for recolonisation on the cessation of impacts. While susceptible to large scale loss from severe storms these meadows were quick to re-establish compared with nearby shallow coastal seagrasses. The results of the work are establishing a series of key management thresholds and stress indictors that can be applied to ensure greater protection of these seagrasses.