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Global seaweed aquaculture production has more than tripled since 2002 and is dominated by Asian countries with farming operations that typically occur in relatively wave‐protected, nearshore areas. To meet future demand, production must move to "non‐traditional" regions and into less contested waters offshore. However, the technological complexities and uncertainties in the performance of seaweed cultivated in high‐energy offshore environments are substantial and must be overcome. Here, we identify knowledge gaps and suggest a research roadmap to inform the advancement of a commercial offshore seaweed aquaculture industry using southern Australian species as case studies: (1) Durvillaea spp. (order Fucales); (2) four kelps (order Laminariales); and (3) the rhodophyte Asparagopsis. These groups lie along a spectrum of commercial viability and readiness for offshore aquaculture, and key knowledge gaps are cultivation technology and the suitability to offshore conditions. Cultivation of Durvillaea is restricted by a low level of biological and technical understanding, but there is high market potential and readiness. For laminarian kelps, commercial production in nearshore conditions is already occurring elsewhere, which make them the most likely candidate for offshore cultivation in the medium term. Asparagopsis is least suited to offshore conditions, with substantial gaps in general cultivation knowledge, and its cultivation is likely to be restricted to land‐based systems or relatively sheltered nearshore waters. The knowledge gaps identified here will inform research and development programs to advance offshore seaweed aquaculture in southern Australia and globally. [ABSTRACT FROM AUTHOR]

The IUCN Species Survival Commission has established the Seaweed Specialist Group, which consists of scientists and practitioners from around the world. The group's main objectives are to assess and improve the conservation status of seaweeds, establish networks and partnerships for conservation efforts, and raise awareness about the importance of seaweed species. Seaweeds are found in all oceans and seas, with over 10,000 known marine species. However, climate change and other human activities pose significant threats to seaweeds, including iconic species that form habitats. The group aims to prioritize conservation efforts for key seaweed taxa, such as Laminarian kelps, which are vital for ecosystems and local economies. By 2025, the group plans to assess the conservation status of at least 120 Laminarian species. Researchers and practitioners in relevant fields are encouraged to collaborate and contribute to the group's conservation efforts. [Extracted from the article]

The kelp, Ecklonia radiata, is an abundant subtidal ecosystem engineer in southern Australia. Density‐dependent changes in the abiotic environment engineered by Ecklonia may feedback to affect reproduction and subsequent recruitment. Here, we examined: 1) how the reproductive capacity of Ecklonia individuals in the field (zoospores released · mm−2 reproductive tissue) varied with adult density and time, and 2) how the recruitment of microscopic gametophytes and sporophytes was influenced by zoospore density at two times. Zoospore production did not vary with adult density, with only one month out of ten sampled over a 2‐y period showing a significant effect of density. However, zoospore production varied hugely over time, being generally highest in mid‐autumn and lowest in mid‐late summer. There were strong effects of initial zoospore density on gametophyte and sporophyte recruitment with both a minimum and an optimum zoospore density for sporophyte recruitment, but these varied in time. Almost no sporophytes developed when initial zoospore density was <6.5 · mm−2 in spring or <0.5 · mm−2 in winter with optimum densities of 90‐355 · mm−2 in spring and 21‐261 · mm−2 in winter, which resulted in relatively high recruitment of 4‐7 sporophytes · mm−2. Sporophyte recruitment declined at initial zoospore densities >335 · mm−2 in spring and >261 · mm−2 in winter and was zero at very high zoospore densities. These findings suggest that although adult Ecklonia density does not affect per‐capita zoospore production, because there is a minimum zoospore density for sporophyte production, a decline in population‐level output could feedback to impact recruitment. [ABSTRACT FROM AUTHOR]

The guidebook walks users through: (1) What is a kelp forest and why they are important, (2) How to know whether kelp restoration is needed, (3) How to engage with local communities to plan restoration, (4) What steps are needed before you attempt restoration, (5) What methods are available for kelp restoration, (6) How to monitor and report on the outcomes of restoration activities, and (7) How to consider climate change and warming oceans in restoration efforts. We are achieving this goal using multiple approaches, including reviewing available data on kelp restoration, establishing a kelp restoration database, authoring a kelp restoration guidebook, raising awareness of kelp forests, and are moving forward to host a kelp restoration summit and set an international restoration target for kelp forests over the next two decades. [Extracted from the article]

Habitat‐forming ecosystem engineers are the foundation of many marine ecosystems where they support diverse and productive food‐webs. A reduction in their patch size or density may affect the productivity, biodiversity and stability of these ecosystems. We determined the effects of different densities and patch sizes of Ecklonia radiata (the dominant kelp in southern Australia) on the secondary productivity, species richness, diversity and community structure of understory epifaunal invertebrates and how associated environmental covariates modified by kelp affected those patterns. We assessed sub‐canopy epifauna across 28 artificial reefs with transplanted E. radiata consisting of seven different patch sizes (0.12–7.68 m2) crossed with four kelp densities (0–16 kelp m−2) over two years. Epifaunal secondary productivity associated with both natural algal and standardised rope fibre habitats decreased with patch size and was elevated when kelp was absent, however, it was also high in natural habitat when there was a high density of kelp. Epifaunal productivity was positively associated with sub‐canopy light and water flow but negatively associated with the biomass of the dominant understory alga, Ulva sp. Epifaunal diversity declined with a reduction in reef size as did richness which correlated with a loss of algal species richness. Community structure of epifauna also differed between small and large reefs, between reefs with and without kelp, between rope habitats at the centre and at the edge of reefs, and within natural habitat between reefs supporting high and low densities of kelp. Overall, these results indicate complex effects of E. radiata decline on epifaunal communities, with high secondary productivity associated with dense kelp stands, but also areas without kelp that are dominated by turf algae. While the loss of standing kelp from rocky reefs may result in declines in epifaunal biodiversity, where turf algae replaces kelp, the reefs may still support high secondary productivity. [ABSTRACT FROM AUTHOR]

Kelp forests are threatened by ocean warming, yet effects of co-occurring drivers such as CO 2 are rarely considered when predicting their performance in the future. In Australia, the kelp Ecklonia radiata forms extensive forests across seawater temperatures of approximately 7-26°C. Cool-edge populations are typically considered more thermally tolerant than their warm-edge counterparts but this ignores the possibility of local adaptation. Moreover, it is unknown whether elevated CO 2 can mitigate negative effects of warming. To identify whether elevated CO 2 could improve thermal performance of a cool-edge population of E. radiata , we constructed thermal performance curves for growth and photosynthesis, under both current and elevated CO 2 (approx. 400 and 1000 µatm). We then modelled annual performance under warming scenarios to highlight thermal susceptibility. Elevated CO 2 had minimal effect on growth but increased photosynthesis around the thermal optimum. Thermal optima were approximately 16°C for growth and approximately 18°C for photosynthesis, and modelled performance indicated cool-edge populations may be vulnerable in the future. Our findings demonstrate that elevated CO 2 is unlikely to offset negative effects of ocean warming on the kelp E. radiata and highlight the potential susceptibility of cool-edge populations to ocean warming.