Moderate Light Found to Boost Gracilaria Seaweed Spore Production
A new marine aquaculture study by Sri Wahidah, Idris, and Baiduri from Pangkep State Agricultural Polytechnic found that moderate light intensity significantly improves the release and attachment of spores in Gracilaria, one of the world’s most commercially important seaweeds. Published in 2026 in the International Journal of Contemporary Sciences, the study identified 1000 lux as the most effective light level for stimulating early reproductive development in laboratory-grown Gracilaria cultures.
The findings are considered important for the global seaweed industry, which continues to expand due to rising demand for agar, food ingredients, pharmaceuticals, cosmetics, and sustainable aquaculture products. Gracilaria seaweed is widely cultivated across Southeast Asia, including Indonesia, because it serves as a major raw material for agar production and marine-based biotechnology industries.
However, one of the biggest challenges in seaweed farming remains the availability of stable, high-quality seedlings. Many seaweed farmers still rely heavily on vegetative propagation, a method that repeatedly uses cuttings from mature plants. Over time, this approach can reduce genetic diversity and lower cultivation performance.
The new research highlights the potential of spore-based propagation as a more sustainable alternative. According to the researchers, optimizing environmental conditions during the reproductive stage is essential for improving seed quality and supporting long-term seaweed cultivation.
The study examined how different light intensities affect the release and attachment of spores from Gracilaria reproductive structures called cystocarps. Researchers tested three light levels—500 lux, 1000 lux, and 1500 lux—under controlled laboratory conditions using a completely randomized experimental design.
Observations were conducted over six days. Researchers measured two main variables:
- The number of spores released into the culture medium
- The number of spores successfully attached to the culture substrate
The released spores were counted using microscopic analysis, while attached spores were observed directly on Petri dish surfaces under stereo microscopes. Statistical analysis was conducted using one-way ANOVA to determine whether differences between treatments were significant.
The results showed a clear pattern: moderate light intensity consistently produced the strongest reproductive response.
The highest spore release occurred under the 1000 lux treatment on day four, reaching 720 ± 35 spores per cystocarp. By comparison, the 500 lux treatment produced only 360 ± 40 spores, while the 1500 lux treatment produced 460 ± 104 spores during the same observation period.
The researchers also found that spore attachment followed a similar trend. The highest attachment rate was recorded on day three under 1000 lux, reaching 520 ± 49 spores per cystocarp. The same treatment also produced the highest average attachment rate overall.
Key findings from the study include:
- 1000 lux produced the highest spore release
- Peak spore release reached 720 ± 35 spores/cystocarp
- Peak spore attachment reached 520 ± 49 spores/cystocarp
- Moderate light outperformed both lower and higher light exposure
- Spore release peaked on day four
- Spore attachment peaked on day three
- Statistical analysis confirmed significant effects of light intensity
The researchers explained that light plays a central role in photosynthesis, which provides the energy needed for growth and reproductive processes in marine algae. Too little light may not provide enough energy for optimal reproduction, while excessive light can create physiological stress that reduces reproductive efficiency.
According to the study, the 1000 lux treatment likely provided the best balance between metabolic stimulation and cellular stability. The researchers noted that increasing light intensity does not always produce better results because reproductive activity in seaweed only operates effectively within a certain physiological range.
The study also identified a distinct reproductive cycle. Spore release gradually increased during the first few days of observation before peaking on day four and declining afterward. Researchers believe this decline may occur because reproductive tissues become exhausted or because most viable spores had already been released.
Similarly, attached spores increased rapidly during the first three days before declining. The researchers explained that this early settlement phase is critical because successful attachment determines whether spores can continue developing into juvenile seaweed plants.
“The present study demonstrates that light intensity is a decisive factor in the early reproductive performance of Gracilaria sp.,” the researchers wrote in their discussion. They added that “1000 lux produced the strongest response in both spore release and spore attachment.”
The implications of the research extend beyond laboratory experiments. For the aquaculture industry, the findings may help hatcheries and seaweed farmers improve seedling production systems by using more precise light management during cultivation.
Improved spore-based propagation could reduce dependence on repeated vegetative cultivation, increase genetic diversity, and produce healthier seaweed stocks for commercial farming. This may help strengthen long-term productivity and sustainability in Indonesia’s seaweed industry, which is one of the largest in the world.
The study also supports broader efforts to develop sustainable marine aquaculture systems as demand for seaweed-based products continues to grow internationally. Global industries increasingly use seaweed in food processing, biodegradable packaging, pharmaceuticals, cosmetics, and biofuel research.
The researchers emphasized that the findings should still be interpreted within the limits of the laboratory environment. Only three light intensities were tested, and other environmental factors such as temperature, nutrients, and salinity were kept constant during the experiment. Further studies are recommended to evaluate more detailed light gradients and examine how other environmental variables interact with light during seaweed reproduction.
Future research is also expected to investigate whether the same light conditions remain effective during later growth stages, including germling development and juvenile thallus formation in hatchery and semi-commercial systems.
Author Profiles
- Sri Wahidah is a marine and aquaculture researcher at Pangkep State Agricultural Polytechnic specializing in seaweed cultivation, marine reproductive biology, and sustainable aquaculture systems.
- Idris is an aquaculture academic affiliated with Pangkep State Agricultural Polytechnic whose research focuses on marine cultivation technology and seaweed hatchery systems.
- Baiduri is a marine biology researcher from Pangkep State Agricultural Polytechnic with expertise in algal physiology, seaweed reproduction, and marine environmental management.
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