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Kelp aquaculture is an emerging industry outside of Asia. To be successful, this industry requires a reliable production of seedstock, the optimisation of which greatly benefits from a detailed physiological understanding of the microscopic life-cycle stages of the cultured species. This study investigated the impact of six zoospore densities (10–278 mm−2) on the subsequent development of Ecklonia radiata gametophytes and sporophytes. The results showed that germination rates and sex ratio were unaffected by initial zoospore density, but there were significant effects on gametophyte size and sporophyte production. After two weeks, female gametophytes were largest at an initial zoospore density of 40 mm−2 while male gametophytes grew largest at densities below 40 mm−2, but after four weeks gametophyte size showed a negative relationship with initial zoospore density. Significantly more sporophytes developed at initial zoospore densities below 40 individuals mm−2 and no sporophytes were observed at the highest density (271 zoospores mm−2). These results clearly show the importance of initial zoospore density in optimising the nursery stage of kelp aquaculture. [ABSTRACT FROM AUTHOR]

Large-scale seaweed aquaculture in the ocean is being pursued globally as a solution to many contemporary challenges, including climate change, food security, and ecosystem degradation. However, the required development and transformation of marine systems for farming may have unknown implications for sustainability objectives, such as those outlined in the United Nations Sustainable Development Goals (SDGs). The aim of this paper is to outline the opportunities for, and threats from, seaweed farming in the context of sustainability. We synthesise the perspectives of expert stakeholders from multiple sectors through a series of Australian workshops to catalogue the pathways through which seaweed farming may affect sustainability, giving specific focus to the SDGs. In doing so, this study illustrates that seaweed farming has the potential to influence, to some degree, the majority of SDGs, with both positive and negative influences. Indeed, seaweed farming is most likely to benefit progress towards achieving SDGs 2 (Zero Hunger), 8 (Decent Work and Economic Growth), 9 (Industry, Innovation, and Infrastructure), 12 (Sustainable Production and Consumption), and 15 (Life on Land). But expectations of seaweed farming may also fall short for supporting some goals if appropriate measures are not implemented to mitigate potential impacts, most notably SDG 14 (Life Below Water). We underscore that seaweed farming has the potential to contribute to sustainable development, and that this potential can only be realised with appropriate regulation and mitigation to avoid unwanted negative outcomes. Better identification and management of trade-offs between these potential positive and negative outcomes across sustainability domains, will be critical for realising the full potential of seaweed aquaculture for sustainable development. [ABSTRACT FROM AUTHOR]

Seeding twines are convienient for outplanting cultured seaweeds, facilitating seeding in high densities. Twines are typically made of synthetic polymer fibres, likely for increased durability and economic benefits relative to natural fibres. However, synthetic twines can contribute to oceanic plastic pollution if fragmented or lost at sea, whereas natural-fibre twines will biodegrade over time. We compared the seeding success of zygotes and germlings of the fucoid Phyllospora comosa among different twines varying in diameter and composition (nylon (1 mm & 3 mm), Kuralon (2 mm & 3 mm) and Algae Twine™ (1 mm) and hemp (1 mm) in three separate experiments (A, B & C). For experiments A and B (both six weeks duration), equal densities of P. comosa embryos were seeded directly onto twines wrapped tightly around 20-cm lengths of 50-mm diameter PVC pipe and cultured indoors in controlled conditions. For experiment C (three-months duration) equal sections of each twine were wrapped in a randomised order around replicate quadrats (50 cm × 50 cm) and cultured in large flow through outdoor tanks. Successful seeding of P. comosa zygotes occurred on all twines in all three experiments, but differences in length, percentage cover and densities varied among twine types across times, and between experiments. Germlings had reached ~ 1-mm lengths by 9 weeks of age in Experiment A, but similar lengths were reached by 4 weeks in Experiment B. In Experiment C, germlings had attained ~1.7 mm by 12 weeks on all twines except hemp. This study demonstrates that whilst 2-mm Kuralon twine generally performed well, a range of twine types may be suitable for seeding and subsequent hatchery growth of P. comosa embryos, including the natural twine, hemp. Farmers may thus effectively base their choice of seeding twine on the cost of material versus environmental trade-offs of using natural versus synthetic twines. However, performance of the different twines at sea remain to be tested in future studies. • Demand for seaweeds is creating opportunities for culture of novel seaweed species. • Synthetic twines for seeding seaweeds contribute to oceanic plastic pollution. • Phyllospora comosa seeded on twines varying in composition and diameter. • Farmers may base twine choice on material cost versus environmental trade-offs. • Future studies of performance of different seeded twines deployed at sea are needed. [ABSTRACT FROM AUTHOR]