Laboratory and aquaculture experiments show that strong light is a key to suppressing the early-stage growth of Undaria pinnatifida
摘要
The brown macroalga Undaria pinnatifida has been introduced from Asia to the world and is now cultivated worldwide as a commercially important species. One notable problem that occurs during U. pinnatifida cultivation is that juvenile sporophytes of often disappear immediately after the start of cultivation, which is likely due to both abiotic or biotic factors. Previous studies showed that juvenile sporophytes are susceptible to abiotic factors such as high temperature, nutrient-poor conditions, and strong light; however, which of these factors are important for early-stage growth remains to be determined. We investigated the combined effects of 7 temperatures (12–24ºC), two light intensities (50 and 200 µmol photons m⁻2 s⁻1), and nutrient enrichment (i.e., non-enriched and enriched) on the relative growth rate and chlorophyll a (chl-a) content of juvenile sporophytes under controlled laboratory conditions. The relative growth rate generally declined with increasing temperature, which was driven by increased light intensity; nutrient enrichment did not appear to be a factor. The chl-a concentration generally increased with increasing temperature under the low light treatment but was not observed under high light; nutrient enrichment did not influence these observations. We suggest that high light intensity, rather than no nutrient enrichment affects U. pinnatifida juvenile sporophytes, especially under high temperature. An experiment conducted at an aquaculture farm suggest that an aquaculture rope set at a lower depth during the early life-stages led to greater growth and production. Strong light will be a critical factor that suppresses the growth of juvenile sporophytes during cultivation and yield of this U. pinnatifida, especially as water temperatures continue to increase under climate change.