Saccharina latissima is a perennial kelp with a circumboreal distribution from the North Pacific to the North Atlantic coasts. Our study clarified the taxonomy of the morphologically distinct Sacch...

To create carbon efficient sources of bioenergy feedstocks and feedstuff for aquaculture and terrestrial livestock, it is critical to develop and commercialize the most efficient seaweed cultivation approach with a sustainable nutrient input supply. Here, we present data for a novel, onshore tropical macroalgae cultivation system, based on influent deep seawater as the nutrient and carbon sources. Two red algal species were selected, Agardhiella subulata and Halymenia hawaiiana, as the basis for growth optimization. Highest productivity in small-scale cultivation was demonstrated with A. subulata in the 10% deep seawater (64.7 µg N L⁻¹) treatment, growing at up to 26% specific growth rate day⁻¹ with highest yields observed at 247.5 g m⁻² day⁻¹ fresh weight. The highest yields for H. hawaiiana were measured with the addition of 10% deep seawater up to 8.8% specific growth rate day⁻¹ and yields at 63.3 g fresh weight m⁻² day⁻¹ equivalent. Biomass should be culled weekly or biweekly to avoid density limitations, which likely contributed to a decrease in SGR over time. With a measured 30–40% carbon content of the ash-free dry weight (20–30% of the dry weight) biomass, this translates to an almost 1:1 CO₂ capture to biomass ratio. The compositional fingerprint of the high carbohydrate content of both Agardhiella and Halymenia makes for an attractive feedstock for downstream biorefinery applications. By focusing on scaling and optimizing seaweed farming technologies for large-scale onshore farms, the opportunities for yield potential, adaptability to cultivation conditions, and meeting global sustainability goals through novel, carbon-negative biomass sources such as seaweed can be realized.

The biogeographic area between Cape Mendocino, California and Cape Blanco, Oregon in the USA spans over 320 km and is characterized by prominent coastal headlands. This study was a first attempt to produce a current intertidal macroalgal and seagrass species list for this understudied region with basic habitat attributes included. A total of 164 species of marine macroalgae (105 species within 16 orders in Rhodophyta, 32 species within six orders in Heterokontophyta, Phaeophyceae, and 27 species in six orders in Chlorophyta) and two species of seagrasses (Anthophyta) were identified. The optimal habitat for most species was the rocky intertidal in the mid zone (>50%), while some species were specialists in either tidepool and/or sandy habitats (∼20%). Furthermore, based on Akaike Information Criterion, our top ranking model suggests that species richness is dependent on zonation, functional grouping and site location. Based on the seven functional group classification, the leathery macrophytes and crusts were the most prevalent at the two capes exposed to higher wave action and upwelling. One near-endemic species (Cumathamnion sympodophyllum), one invasive species (Sargassum muticum), and seven new records for the region were identified.