Sporelings and growth of the marine red alga, Gelidium elegans (Gelidiaceae), from Northern Taiwan

Gelidium elegans is a marine red alga widely distributed in the northwestern Pacific Ocean. In Taiwan, wild populations of G. elegans have been gradually declining over the past decade due to global warming and overharvesting. Two types of cultivation experiments with G. elegans were conducted: spore germination experiments under four different temperature conditions and a growth experiment to test the growth condition and longevity of G. elegans in a controlled environment. The sporeling temperatures were set to simulate seawater temperatures between 18 °C and 25 °C, corresponding to seawater temperatures from March to May in Northern Taiwan. This period aligns with the peak growth season for G. elegans. The purpose of this setup was to provide optimal conditions for the germination and growth of seedlings of G. elegans for indoor cultivation. Most of the tetraspores germinated into seedlings under the four temperature conditions (18 °C, 20 °C, 22 °C, 25 °C). However, the seedlings grown between 22 °C and 25 °C stopped growing and turned white after 30–50 days of cultivation. On the other hand, the juveniles cultivated at 18 °C reached adult size (more than 10 cm in length) after more than a year of cultivation in the laboratory. In comparison, the juveniles at 20 °C grew slower than those at 18 °C. In the longevity experiment, the subculture thalli thrived well after three years of cultivation in a controlled environment. Next, outdoor culture experiments will be conducted under natural conditions with different nutrient and irradiance regimes to test the sensitivity of juveniles to water temperature.