Selection of temperate Ulva species and cultivars for land-based cultivation and biomass applications

Green seaweeds from the cosmopolitan genus Ulva are targets for land-based aquaculture and a diverse range of biomass applications, but are not currently cultivated in Aotearoa New Zealand. Therefore, the objective of this study was to identify target species and cultivars of Ulva as a first step towards establishing land-based cultivation of seaweed in Aotearoa New Zealand. We isolated 24 cultivars of Ulva from natural populations in the Bay of Plenty region of New Zealand. We compared growth and biomass productivities of 18 of these cultivars, either in their original collection morphology (e.g., blade/filamentous) and/or in cluster morphology where possible as a result of induced formation of free-floating germling clusters. Specific growth rates and biomass productivities of multiple cultivars in small-scale laboratory cultures were high (>20% day−1 and >8 g dry weight (DW) m−2 day−1 respectively), with biomass increases of 5 to 8-fold per week in the fastest growing cultivars. However, there was significant variation in growth and biomass productivity among cultivars of each morphology type. Biomass productivities were highest for cultivars WB2 (blade, 7.5 g DW m−2 day−1), SW9 (blade cluster, 9.4 g DW m−2 day−1), SW8 (filamentous, 7.8 g DW m−2 day−1), and SW6 (filamentous cluster, 9.8 g DW m−2 day−1). Growth rates and biomass productivities were consistently higher for cluster compared to non-cluster morphologies for each morphology type (e.g. filamentous or blade), demonstrating that clusters are a viable option to enable free-floating cultivation of filamentous species of Ulva. These results confirm the suitability of Ulva as a target for intensive land-based aquaculture in Aotearoa New Zealand. The significant inter-cultivar variation found in the current study further highlights the importance of sampling widely and focusing on cultivar rather than species selection when identifying targets for cultivation.