Reproductive output and productivity of filamentous tropical Ulva over time

The production of macroalgae in the tropics requires robust species that tolerate temperature and salinity fluctuations. The widely distributed macroalga Ulva sp. 3 is tolerant of these environmental challenges; however, a reliable source of seedlings and a consistent production of biomass are critical for the sustainable long-term cultivation of this species. Therefore, the objective of this study was to quantify the reproductive output and productivity of multiple cultivation cycles of the asexually reproducing Ulva sp. 3 seeded onto ropes using the harvested biomass of each cycle as the seedstock for each successive generation. The seedstock of three independent collections was assessed across multiple asexual generations in outdoor culture to investigate generational and environmental effects. This study, for the first time, has demonstrated that Ulva sp. 3 can be cultivated successfully over multiple (up to seven) successive generations and highlighted the importance of generational and environmental effects. Notably, there was an order of a magnitude decrease in reproductive output and greater than 4-fold decrease in biomass productivity across generations, while the decrease across cultivation cycles was more pronounced with a greater than 20-fold decrease in reproductive output and an order of a magnitude decrease in biomass productivity. The marked decrease in reproduction and productivity was driven by a generational effect in combination with environmental effect across the multi-generational study and both require consideration for the intensive production of biomass.