Effects of extrinsic abiotic factors on induction of gametogenesis and efficacy of a device for the segregation of non-fused gametes and zygotes in the green alga Ulva lactuca

Seaweed aquaculture is one of the fastest growing marine sectors with 31.2 million tonnes year–1 of harvest worth over 11.7 billion USD. Commercial operations still rely on traditional techniques but innovative strategies are essential for future expansion. The present paper reports on a simple device that could effectively segregate non-fused haploid gametes from diploid zygotes in the green alga Ulva lactuca. The differential phototactic behaviour of gametes and zygotes was used for their separation. Approximately 56.2% non-fused haploid gametes and 5.3% diploid zygotes were separated after 5 min and after 1 hr and 2 hr, the composition of gametes was 26.6 and 8.8%, respectively while that of zygotes 32.7 and 57.4%, respectively. The effects of extrinsic abiotic factors, including light, temperature, salinity, photoperiod, dehydration and thallus fragmentation, on the induction of gametogenesis was found to be limited at 35°C (13.33 ± 5.77%) and a short day 9:15 h light:dark photoperiod (20 ± 4.08%), while dehydration treatments enhanced spore induction. This study demonstrated the efficient and cost-effective utilisation of locally available materials in producing a simple, small, precise, durable and easy to use system, which also saved on energy. The effective segregation of non-fused gametes from zygotes aids in cytological preparation, bio-chemical characterisation investigations as well as breeding and hybridisation all of which have direct implications on the future farming of Ulva and other species of seaweeds with similar life phases.