Population status and lunar periodicity of spawning of Tripneustes gratilla (Echinodermata: Echinoidea), in Jose Abad Santos, Davao Occidental, Philippines

The population structure and lunar periodicity of spawning were investigated from January to February 2024 across three sites in Jose Abad Santos, Davao Occidental, Philippines. Monthly field surveys were conducted using the belt transect method to assess population structure, while laboratory analyses were performed to examine the lunar periodicity of spawning across different lunar phases. A total of 160 individuals of Tripneustes gratilla (Linnaeus 1758) were recorded with an estimated mean density of 645.83 ± 171.50 ind ha-1 and mainly dominated by adult size classes having a test diameter (TD) of 61 - 65 mm followed by pre-adults of 51 - 55 mm TD and only very few recruits 33 – 40 mm TD. The relationship between the TD and weight of T. gratilla displayed a high positive correlation. It exhibited a negative allometric growth with a b value of less than 3 in three sites. The result of the gonad index (GI) and fecundity showed that the highest GI and total number of eggs occurred during the full moon while the lowest occurred during the new moon with notes on sexual maturity at 54 mm TD. While the findings of this study provide valuable insights, they are not conclusive regarding the population structure and lunar spawning periodicity, as the study was conducted over only two months. Long-term monitoring is needed for a more accurate understanding of the status of T. gratilla at these sites.