Longer storage, brighter light? – Testing artificial gamete release and fertilisation of Fucus vesiculosus for aquaculture

Macroalgae aquaculture is an emerging field in Europe, with potential for the production of food and biomedical compounds, as well as nutrient cycling. Macroalgae harvest could become an internal nutrient removal strategy in the eutrophic Baltic Sea. Due to low salinity, seaweed aquaculture is limited to a few favourable species, with Fucus vesiculosus as a promising candidate. Its feasibility in offshore cultivation is tested in long-line aquaculture. For this approach F. vesiculosus seedlings are artificially reproduced and cultivated. To fulfill the requirements of aquaculture, like flexible sowing times and a more predictable seedling production, protocols for gamete isolation and fertilisation need to be optimised further. The present study investigated artificial reproduction of F. vesiculosus populations from Kiel Fjord in three experiments in May, June, and September. The effect of receptacle storage condition, storage duration, and light intensity as factors for stress-induced gamete release and the effect on germination success was investigated in the laboratory. The amount of gametes released per receptacle and the percentage of successfully germinated zygotes were quantified. Results of this study indicate that gamete release is most efficient after 2-3 weeks of wet receptacle storage. In contrast, dry receptacle storage is only feasible for a duration of one week, whereas longer dry storage hinders gamete release. Bright light of 250-500 μmolm−2 s−1 leads to successful gamete release. Germination success was not significantly impacted by storage treatments or light intensity, but showed a tendency of lower germination success after longer storage. Even with the optimised treatments, gamete release rates fluctuated greatly between seasons and populations. To produce reliable amounts of seedlings for aquaculture, further research is needed.