Optimal spawning conditions of Phyllospora comosa (Phaeophyceae, Fucales) for mariculture

The fucoid Phyllospora comosa has sparked interest from the industry as a potential commercial aquaculture species. However, information on the feasibility of culturing this species, including maximising spawning and fertilisation, remains limited. This study aimed to identify optimal conditions for spawning and early development of P. comosa under laboratory conditions. We tested spawning and germination success across lunar phase (new moon vs full moon), temperature (15 °C, 18 °C, 21 °C), light (35 μmol photons m−2 s−1 vs 0 μmol photons m−2 s−1) and exposure (desiccated vs submerged). Lunar cycles were compared over three consecutive months. Fifty fertile P. comosa male and female thalli were collected from Port Fairy, Victoria, Australia, every 2 weeks to coincide with full and new moon phases from February to April 2017. Spawning of eggs and sperm was achieved in all treatment combinations. However, there was no consistent effect of lunar phase, light, temperature or exposure, with high temporal variability amongst treatment groups. Percentage germination after 24 h in static culture varied between 35 and 90%, and overall embryo mortality was high (> 65%) after 7 days, but did not differ amongst spawning cue treatments. The high mortality observed at day 7 did not appear to be linked to insufficient egg or sperm densities nor excess sperm (polyspermy). Overall results indicate flexibility in spawning conditions which is advantageous for integration into aquaculture.