Tripneustes gratilla is a commercially valuable sea urchin known for its edible gonads, rapid growth, and aquaculture potential. However, large-scale production is limited by gaps in knowledge about optimal rearing conditions, particularly light exposure. The species displays covering behavior, likely in response to solar radiation or predation. This study examines the effects of solar radiation on T. gratilla in Seychelles to guide aquaculture practices and enhance production efficiency.
Methodology
Four experiments (exp) were conducted in fiberglass raceways. Exp1: 12 T. gratilla were offered opaque, semi_transparent, and transparent plastic pieces; number of collected plastic pieces were recorded after 3 hours. Exp 2: 12 T. gratilla were exposed to 0%, 32%, 41%, and 77% shade using overhead materials on their respective crates; the number of collected plastic pieces (opaque, semi-transparent, and transparent) was recorded after 30 minutes. Exp 3: 60 T.gratilla were placed under 0%, 37%, and 100% shade; righting time was measured after 3 hours. Exp 4: 90 T. gratilla were reared under 0%, 37%, and 100% shade treatments for 67 days; growth, fitness, survival, disease, and GSI were monitored.
Results
No significant preference for cover materials was found (p = 0.765) in experiment 1, suggesting shading capacity does not drive covering material selection. However, in the second experiment higher light intensity significantly increased the number of materials collected (p = 0.049), indicating a behavioural response to solar exposure (Figure 1). In the third experiment short-term exposure to high light significantly reduced righting ability in urchins (p = 0.027), implying stress under sudden changes (Figure 2). In contrast, in experiment 4 the long-term exposure (67 days) showed no significant differences in fitness, growth, mortality, disease, or gonad index across light treatments (p > 0.128), highlighting their capacity to acclimate.
Conclusion
While short-term light exposure negatively affects fitness, the species appears capable of acclimatizing to different light levels over time. Covering behavior increases under intense light but is not dependent on material opacity. Overall, shading may not be necessary for long-term urchin production, highlighting the potential to simplify aquaculture systems while maintaining animal welfare and productivity.