The red seaweed Asparagopsis taxiformis can reduce methane emissions in livestock by over 90

Elevated terrestrial nutrient loads entering coastal waters in northeastern Australia are adversely affecting the Great Barrier Reef World Heritage Area. ‘Seaweed biofilters’ have been proposed as a mechanism for the bioextraction of elevated nutrient levels from coastal environments, with potential to target diffuse source nutrient discharges while generating biomass with potential applications as fertiliser, soil conditioning agents and agricultural fodder. Here, we use a novel modelling approach to identify optimal candidate locations for seaweed biofilter deployment in northeastern Australia’s coastal waters, prioritising sites for more detailed assessment and on-ground feasibility evaluation. The analysis integrates spatial layers representing regulatory constraints and practical deployment considerations with a model for the seaweed growth potential. Growth potential is determined from outputs of the Environmental Modelling System (EMS), a sophisticated environmental model that simulates coupled physical, chemical, and biological processes and is continuously operated over the Great Barrier Reef region as part of the eReefs project. Based on this analysis, fourteen sites, located near river mouths, satisfied the selection criteria and were identified as potential candidates for seaweed biofilter deployment. Potential sites for seaweed biofilters in the Great Barrier Reef identified using legal and practical criteria. Identified over 800,000 ha of coastal waters as potentially suitable for seaweed cultivation. eReefs biogeochemical simulations used to estimate spatial variability in seaweed growth potential. Fourteen sites shortlisted for further assessment of seaweed mariculture for nutrient biofiltration.

The red seaweed Asparagopsis taxiformis (common name: red sea plume) is attracting global attention because of its ability to reduce methane emissions in livestock systems. However, its habitat and distribution within the Great Barrier Reef (GBR)-one of the world's most iconic marine ecosystems-remain largely unexplored, posing challenges for conservation and the sustainable development of the seaweed industry. To help bridge this gap, we used habitat suitability modelling to identify areas in the GBR with favourable environmental conditions for A. taxiformis. We combined traditional and community-contributed data with marine spatial datasets to generate a predictive model using a machine learning approach (MaxEnt). Our findings indicate that A. taxiformis may occupy a broad habitat range along the GBR, spanning nearshore and offshore areas from the northern to southern sectors, albeit with some gaps. These potential habitats include areas with no previous records. Highly suitable habitats were found in areas with water depth of less than 20 m, minimum average seawater velocities of 0.3-0.5 m s-1, and minimum photosynthetically active radiation levels of 25-28 E m-2 day-1. Future projections suggest that more areas will become more suitable by 2050, possibly indicating habitat expansion. The identification of unreported potential habitats of A. taxiformis in the GBR provides a foundation for targeted monitoring and adaptive conservation and management strategies at both species and ecosystem levels.

The red seaweed Asparagopsis taxiformis has the potential to reduce methane emissions from livestock, but key challenges remain in developing scalable, ocean-based cultivation protocols using a closed-lifecycle approach. A critical milestone in this effort is developing seeding methodologies and identifying effective substrates for the attachment of gametophyte germlings. This study evaluates the suitability of synthetic and natural twine substrates and a sodium alginate binder for A. taxiformis germling cultivation under laboratory conditions. Polypropylene, nylon, cotton and sisal twines and a smooth polypropylene control surface were seeded with a germling solution, either directly or within a sodium alginate binder. Germling cover (%) was assessed after six weeks of tank-based cultivation and again following unravelling and exposure to moderate-velocity flow to simulate ocean deployment conditions. Polypropylene twine retained the highest germling cover (104% cover post-exposure), while cotton twine (70% cover) showed promise as a biodegradable alternative. Reduced germling cover was observed on the sodium alginate binder treatments across the majority of substrates, with germling loss particularly high (81% reduction in cover) on the smooth surface of the polypropylene control. By demonstrating a scalable seeding methodology and identifying two effective, widely available substrates for cultivation; polypropylene and cotton twine, this study provides a foundation for developing seeded twine for A. taxiformis mariculture. Field trials will be essential to validate this nursery-stage performance at-sea. Ultimately, optimising seeding techniques and cultivation substrates will be key to scaling A. taxiformis mariculture and unlocking its potential for sustainable bioproduct applications.

Seagrass meadows continue to be lost and degraded globally. Restoration is one promising and emerging conservation strategy to combat such losses and place seagrass on a pathway to net gain. However, successful restoration methods remain limited to a few species, and geographically constrained, with few experimental trials comparing planting methods across species and seagrass bioregions. This study trialled three seed-based seagrass restoration planting methods in two seagrass bioregions (the temperate north Atlantic and temperate southern oceans). Using two seagrass species Zostera marina and Zostera muelleri this research investigated seed-based planting methods and their influence on the likelihood of seedling emergence, shoot emergence, and seedling growth (i.e. leaf length). Seagrass emergence was observed at 50 % of the experimental sites, with the likelihood of seagrass emergence largely influenced by local site conditions. Each planting method performed variably in relation to species and environmental conditions. Dispenser injection seeding resulted in the highest shoot emergence efficiency of the three methods for Z. marina while biodegradable planting pots and hessian bags were the more favourable methods for use with Z. muelleri seeds. Despite all chosen sites deemed suitable for restoration from habitat suitability models, low seedling emergence suggests that site conditions including wind fetch, redox boundary depth and mud- dominant sediments present specific bottlenecks to seed germination and retention. This work demonstrates the importance of matching seed planting methods to site conditions and species life history traits and highlights the need for greater understanding of mechanisms to overcome germination and emergence bottlenecks in seed-based restoration.

Seagrass meadows are under increasing pressure from anthropogenic activities, which are contributing to global declines. Seagrass vegetative fragment dispersal can assist natural meadow recovery and can be influenced by winds, currents and marine animals (e.g. bioturbation). Fragment viability can also affect dispersal, settlement and establishment, ultimately impacting successful recruitment to an area, as well as resilience and metapopulation dynamics. Here, we investigated the viability of Zostera muelleri and Halophila ovalis fragments sourced from the water column and experimentally detached fragments collected from intertidal beds by mimicking megaherbivore foraging behaviours. We evaluated fragment settlement and root establishment, and viability and growth rates for 1 mo in an outdoor mesocosm experiment. Plant morphometrics were measured before and after the experiment to evaluate their influence on fragment settlement and root establishment. H. ovalis settlement was influenced by rhizome length, and Z. muelleri settlement was influenced by the number of shoots and shoot length. Root establishment was limited for both species, with no relation to plant morphometrics. Experimentally grazed fragments of both species showed a faster rhizome elongation rate than naturally floating fragments, and H. ovalis exhibited the fastest rhizome elongation rate. Naturally floating and experimentally grazed fragments also had similar viability. Ultimately, our results suggest that root establishment in the sediment is the rate-limiting step in fragment reattachment. Fragments actively grew fresh rhizomes and were equally viable for both species, indicating they are ecologically functional propagules. Root establishment potential requires further study, as it determines the success of natural seagrass reestablishment from vegetative fragments.

Large-scale mangrove restoration initiatives have been attempted worldwide but have often suffered from low success rates and high costs. Direct seeding is increasingly used as a viable and cost-effective strategy for achieving restoration at scale for other coastal habitats yet has been little used for mangroves. Planting mangrove propagules instead of saplings can reduce costs and labour associated with the collection, growing out, and replanting involved in conventional restoration methods. In this study, we document research into direct seeding for mangrove restoration, focussing on early establishment processes and identifying recruitment enhancement strategies that will improve natural recruitment success rates. The elongated propagules produced by Rhizophoraceae species can establish by self-planting into the substrate, or after grounding flat as the tide recedes. An aquaria experiment showed that vertically sown (to simulate self-planting) Rhizophora stylosa propagules grew significantly longer and more roots than propagules sown horizontally. After 35 days the vertical propagules grew roots 46.3 +/- 20.5 mm in length while horizontal propagules grew roots 17.4 +/- 16.6 mm in length. A field study showed that specially designed bamboo structures facilitate vertical self-planting, thus enhancing successful establishment. Propagules grounding in a vertical orientation successfully established 52.6 % of the time, whereas propagules grounding horizontally had a 10 % success rate. Results from this study suggest that grounding orientation, and the hypocotyl being embedded into the substrate, prompt root initiation and may lead to R. stylosa reaching an establishment threshold quicker than naturally stranding propagules. As such we propose that direct seed planting represents a viable alternative for large-scale restoration of Rhizophora.

Introduction The structure and function of seagrass habitats are essential for supporting ecosystem services and ensuring ecosystems resilience. However, seagrass ecosystems are continuing to decline globally. Restoration initiatives are increasingly adopted to help curb these losses and accelerate ecosystem recovery.Objectives This study sought to rapidly increase seagrass cover and structural complexity of a fragmented but recovering intertidal seagrass meadow.Methods To do this, we conducted in situ field experiments using four seed-based restoration planting methods: hessian bags, clay seed balls, dispenser injection seeding (DIS), and planting seedlings. Changes in seagrass cover and structural complexity were monitored for a 6-month period and compared to natural meadow recovery.Results Our results showed few differences in seagrass cover and structural complexity across the experimental planting methods. DIS showed marginally favorable results compared to other methods at sustaining cover throughout the experimental period. Seasonality was found to substantially influence seagrass traits, with marginal decreases in growth in planted plots observed when seasonal influence was removed.Conclusions These results indicate that both direct seeding and planting seedlings could potentially be used for enhancing seagrass recovery in low density meadows; however, method selection and meadow seasonal dynamics should be given careful consideration to facilitate rapid meadow recovery.

Cultivation of the red macroalga Asparagopsis is gaining momentum as a source of methane reducing feed additives and for nutrient bioremediation, with current farming focused on the tetrasporophyte stage. Advancing Asparagopsis cultivation offers significant environmental and economic benefits. Tetrasporophytes are vulnerable to epiphytic contamination by filamentous algae, adversely impacting both productivity and product quality. This study employed morphological and molecular analyses to identify an unknown red macroalga, growing epiphytically on Asparagopsis taxiformis tetrasporophytes, as Colaconema cf. infestans. Colaconema cf. infestans infestation has the potential to disrupt Asparagopsis farming and impose significant operational and economic costs. We employed a systematic approach to evaluate 57 treatments derived from nine chemicals for eradicating C. cf. infestans from A. taxiformis tetrasporophyte cultures isolated from Queensland, Australia. Initial screening with pulse-amplitude modulation (PAM) chlorophyll a fluorescence revealed a differential tolerance to chemical treatments between the two algal species, at both one day and one week post-treatment. A subsequent four-week co-culture experiment assessed the efficacy of 13 chemical treatments. Only four treatments (ethanol: 50% for 10 seconds, applied twice per week, and sodium hypochlorite: 2% for 5 minutes, applied at any frequency) resulted in an absence of visible C. cf. infestans contamination across all replicates. However, these treatments also caused significant Asparagopsis bleaching (98.8-100.0%) and thus do not represent a viable solution for contamination management. In the absence of an effective solution, this study emphasizes the importance of regular monitoring to allow early detection and explores potential future strategies for contamination management.

Seagrass restoration can reverse trajectories of decline and foster the return of lost ecosystem services, however, poor site selection can hinder restoration success. Suitability modelling is increasingly used to identify contemporary restoration areas, but suitability can change due to environmental perturbations, potentially rendering areas unsuitable under different scenarios (E.g. climate change). Thus, there is a need for restoration practitioners to both identify contemporary areas for restoration and shortlist those resilient to environmental change. Here we use Western Port, Victoria, Australia as a case study demonstrating how forecasted suitability models can identify resilient areas for seagrass restoration and avoid areas that may be unsuitable under future forecasts (risky sites). Initially, the random forest algorithm was used to identify contemporary intertidal and subtidal seagrass restoration areas. Once identified, the resilience of these areas was assessed using environmental scenarios representing degradations to local light environments and climate change related variables (temperature, solar radiation, depth, and salinity). Models initially identified 161 km2 of areas suitable for seagrass restoration. However, only 71% (115 km2) remained suitable under 2030 climate change projections, and 62% (100 km2) remained suitable under 2090 projections. Both 2030 and 2090 projections predicted reductions in suitability in areas that were still identified as suitable for restoration in the future, suggesting climate change may both reduce the areal extent of areas for restoration and reduce their quality. Approaches used here can be transferred to other restoration programs worldwide and across taxa and demonstrate the benefits of forecasting restoration suitability to avoid risk and increase restoration success.

Patchy global data on belowground litter decomposition dynamics limit our capacity to discern the drivers of carbon preservation and storage across inland and coastal wetlands. We performed a global, multiyear study in over 180 wetlands across 28 countries and 8 macroclimates using standardized litter as measures of "recalcitrant" (rooibos tea) and "labile" (green tea) organic matter (OM) decomposition. Freshwater wetlands and tidal marshes had the highest tea mass remaining, indicating a greater potential for carbon preservation in these ecosystems. Recalcitrant OM decomposition increased with elevated temperatures throughout the decay period, e.g., increase from 10 to 20 degrees C corresponded to a 1.46-fold increase in the recalcitrant OM decay rate constant. The effect of elevated temperature on labile OM breakdown was ecosystem-dependent, with tidally influenced wetlands showing limited effects of temperature compared with freshwater wetlands. Based on climatic projections, by 2050 wetland decay constants will increase by 1.8% for labile and 3.1% for recalcitrant OM. Our study highlights the potential for reduction in belowground OM in coastal and inland wetlands under increased warming, but the extent and direction of this effect at a large scale is dependent on ecosystem and OM characteristics. Understanding local versus global drivers is necessary to resolve ecosystem influences on carbon preservation in wetlands.

There is global interest in cultivating the red alga Asparagopsis taxiformis due to its efficacy as a potent anti-methanogenic feed supplement and as a biofilter for the bioremediation of nutrient-enriched waters. However, the development of A. taxiformis cultivation is currently hindered by a lack of information about the conditions required to maximise tetraspore release and thus secure a reliable source of germlings for out-planting. In this study, we examined the effects of temperature, irradiance, and standard nutrient supplementation (F/8, potassium iodide (KI) and arsenic trioxide (As2O3)) on the number of germlings produced per tetrasporophyte, using a strain of A. taxiformis widespread within the Great Barrier Reef, Australia. Temperature, irradiance and nutrient supplementation played a pivotal role in germling numbers, which was optimised at 22 °C under 7 µmol photons m−2 s−1 and with supplementation of F/8 nutrient media, arsenic trioxide (As2O3; 98 µg L−1) and potassium iodide (KI; 166 µg L−1). Once tetrasporophytes were removed from these inducing conditions, tetrasporogenesis ceased within 12 days. In a further five-week experiment investigating the effect of separate supplementation of As2O3 and KI, germling numbers were maximised under supplementation with either As2O3 or As2O3 + KI, with the relative growth rate of tetrasporophytes maximised under supplementation with F/8 + As2O3 + KI. Under optimum conditions, an average of 3,261 ± 826 (SD) germlings were produced per tetrasporophyte over a five-week period. Our results provide a strong starting point for developing hatchery protocols for generating a reliable supply of germlings for nursery cultivation in tropical settings.

The capacity of many macroalgae to rapidly absorb soluble inorganic nutrients and convert them into primary biomass provides opportunities for their use in the bioremediation of nutrient-enriched waters. Marine-based macroalgal cultivation has the potential to target diffuse source nutrient discharges and produce valuable bioproducts such as fertiliser, soil conditioning agents and agricultural feed additives and phycocolloids. Whilst macroalgal diversity offers benefits for improving and maintaining healthy marine ecosystems, it also presents a challenge for determining the best candidate species for cultivation as a nutrient biofilter and, ultimately, a source of bioproducts. We developed and applied a multi-criteria selection model to identify likely candidate macroalgal species for cultivation in Queensland’s coastal waters for biofiltration and bioproduct development, focusing on native species and product development for the agronomical and horticultural sectors. From a species database of 1380 macroalgal species, candidates were initially selected based on their regional abundance, distribution and morphological characteristics considered amenable to in-situ cultivation and harvesting. From a resulting shortlist of 17 species, five systematic literature searches were applied to identify biofilter potential, bioproduct potential and current cultivation status. Of the shortlisted species, Ulva lactuca, Gracilaria edulis and Hypnea cervicornis ranked most highly in the multi-criteria analysis, with several other species showing good potential, but requiring further investment in understanding key biological processes and the development of cultivation protocols.

Seed-based seagrass restoration strategies demand precise understanding of the environmental drivers influencing flowering. Flowering varies across diverse spatial and temporal scales, yet environmental drivers' effects on these dynamics have received less attention. Lack of knowledge regarding this life-history stage limits the advancement of seed-based restoration efforts, especially the establishment of shore-based seagrass nurseries to enhance seed production. A systematic literature review on the flowering of the genus Zostera was conducted to develop a conceptual model that links influential environmental drivers with flowering. Additionally, a case study using existing survey data supplemented by additional field surveys was designed to explore the spatio-temporal variability of flowering along the latitudinal gradient in Australasia for the species Zostera muelleri. Predictive models for flowering times were developed using regional climatic variables, following hypotheses generated from long-term mesocosm observations. The review identified the direct and/or indirect effects of temperature, light, tidal variation, nutrients, salinity and grazing pressure on flowering dynamics. Four categories of flowering variables were identified based on their implications on restoration, namely, timing, abundance, the ratio between reproductive and vegetative growth and morphological characteristics. The spathe densities varied significantly among sites along the latitudinal gradient. While first (r(2) = 0.71) and peak (r(2) = 0.68) flowering times showed significant correlation with latitude, first flowering was equally predicted by mean winter air temperature and mean winter solar radiation (r(2) = 0.73), whereas peak flowering time was best predicted by mean winter air temperature (r(2) = 0.60). Accurate predictions of flowering times can improve conservation outcomes by enabling restoration practitioners to forecast flowering times and subsequent wild seed harvesting. The strong correlation between flowering times and climatic variables suggests future shifts in flowering times under climate change are likely, which is crucial knowledge for maintaining the contribution of restoration projects to seagrass conservation.

Seagrass restoration requires information on a range of factors including site environmental conditions, appropriate planting techniques, and the identification of sites most likely to support seagrass. To address the question of where to focus restoration efforts, a key first step is to identify trends in the spatio‐temporal distribution of seagrasses to identify areas of persistence, loss, and recent gains. Areas of recent recovery (and adjacent areas), can then be targeted by practitioners for assisted recovery and restoration, whilst areas of persistent loss can be avoided. Here we identified the contemporary distribution, density, and species composition of seagrass ecosystems (using Sentinel 2 imagery and supervised object‐based imagery analysis) and integrated these data with historic extents to identify spatio‐temporal trends in seagrass distribution in Western Port, Victoria, Australia. Contemporary classifications demonstrated acceptable accuracies (Overall Accuracy 0.77–0.85, User Accuracy 0.76–0.97) and predicted a contemporary seagrass extent of 222 km 2 ; with 48 km 2 of low‐density recovery predicted to have occurred since 1999. Comparisons with historical seagrass extents indicated some seagrass recovery since large‐scale losses in 1983, although some areas of loss were also present. Recovery included a net gain of approximately 95 km 2 in the past 20 years and an eastward range expansion; suggesting environmental conditions have improved and are now conducive for restoration efforts in some areas. Results demonstrate that accurate, low‐cost, remote sensing of seagrass ecosystems is possible and show how understanding spatio‐temporal trends can guide the spatial allocation of resources by prioritizing areas for restoration where recovery is beginning to occur.

The restoration of seagrass habitats is a relatively young field with several successful restoration attempts highlighting the feasibility of large‐scale restoration. Successful restoration of seagrass habitats requires an understanding of the most appropriate techniques to use for the target species and local conditions of restoration sites, however, there are currently limited studies on Zostera muelleri . Here, we conduct field trials to explore the use of seed‐ and shoot‐based restoration approaches for Z. muelleri in Victoria, Australia. We assessed the feasibility of collecting and germinating seeds in the field for restoration purposes and trialed the success of four shoot‐based transplanting techniques. We found that seed collections for Z. muelleri were highly successful and scalable, with seed collection rates improving from 489 to 1,939 seeds/hour over 2 years. In addition, in situ seedling germination increased from a maximum of 10.80–25.25% over 2 years. In contrast, shoot‐based restoration approaches were more variable, with plants transplanted with their sediment‐intact outperforming all bare‐rooted approaches. Shoot‐based transplanting approaches appear to have more limited application, but may be appropriate for some restoration sites, or used in combination with seeds to achieve the best restoration outcome. Seed‐based approaches have the potential to be viable and scalable for Z. muelleri given that large numbers of seeds can be collected and stored for at least 7 months before successfully germinating in the field. However, further studies are required to overcome the seedling survival bottleneck (approximately 4 months from emergence) and further increase in situ germination rates.

Zostera muelleri is an abundant seagrass species distributed through intertidal and shallow subtidal waters on the subtropical coasts of Australia. The vertical distribution of Zostera is likely defined by tidal influences, particularly desiccation and light reduction stresses. These stresses were expected to affect the flowering of Z. muelleri; however, it is difficult to quantify the effects of tidal inundation with field studies due to multiple confounding environmental factors affecting flowering (e.g., water temperature, herbivory, nutrients). A laboratory aquarium experiment compared the effects of two levels of tidal height (intertidal and subtidal) and light intensity (shaded and unshaded) on flowering timing, abundance, the ratio between flowering shoots and vegetative shoots, the morphology and duration of flower development. The earliest and greatest flowering intensity was recorded in the subtidal-unshaded group, with no flowers observed in the intertidal-shaded group. Notably, the peak flowering time was the same across shaded and unshaded treatments. Shading prolonged the timing of the first flowering and reduced the density of flowering shoots and spathes, while tidal inundation had a more significant effect on the density of flowering shoots and the density of spathes. Results showed that Z. muelleri could flower under low light conditions or tidal stress but not when exposed to both stresses simultaneously in a laboratory ‘nursery setting’. Therefore, applying subtidal-unshaded conditions appears to be beneficial for seagrass nurseries aimed at improved flower abundance despite the plants previously being collected from and adapted to intertidal meadows. Further studies that explore the suitable conditions for triggering and optimising the flowering will be beneficial in designing cost-effective seagrass nurseries.

Flowering is an integral feature of the life history of seagrasses, and it contributes to the genetic diversity and resilience of meadows. There is some evidence that seagrass flowering is influenced by tidal depth; however, the effects of tidal exposure on the flowering variabilities in patchy intertidal meadows are largely unknown. In the present study, inter and intra-annual variability of flowering was examined using a line transect sampling method across two subtropical intertidal meadows (i.e., Lilley’s Beach and Pelican Banks) of Zostera muelleri on Australia’s east coast. Along each transect, the depth was measured using Leica Geosystems AGS14 RTK, and the plant cover was estimated using a standard scale. The duration of exposure at each depth was computed based on the tidal data and categorised exposure duration by hours. The abundance (i.e., the density of flowering shoots and density of spathes) and the ratio of flowering (i.e., flowering frequency) and morphology of flowering (i.e., the number of spathes per flowering shoot) were estimated at every 10 m along three 100 m fixed transects established perpendicular to the tide monthly in 2020 and 2021. Flowering started in July and extended for approximately six months, with peak flowering observed in September-October at both sites. Generalised linear mixed-effect models showed that approximately 39% of the density of flowering shoots, 36% of the density of spathes and 28% of flowering frequency were explained by plant cover and exposure duration. Similar variation in the spathes per flowering shoot was explained by plant cover only (40%). The density of spathes during peak flowering months was significantly different among exposure categories (3-4 hrs and 5-6 hrs in Lilley’s Beach and 5-6 hrs and 6-7 hrs in Pelican Banks in 2021), where significantly different interannual variability was observed only between the same exposure categories in Pelican Banks. The study offers valuable insights into seed-based restoration projects, including optimal seed harvesting times and the average quantity of harvestable flowers, although some inter-annual variations should be anticipated.