Colour Polymorphism of Tridacna crocea Mantle and Its Correlation with Growth Traits

Abstract:

As one of the main members in coral reef ecosystems, giant clams have important economic and ecological value. The conspicuous, brightly coloured mantle shared by all giant clams is a unique feature distinct from other bivalve mollusks and plays an important role in energy harvesting and privacy protection. The boring giant clam Tridacna crocea is usually found at depths of 0.5~3.5 m and is one of the most colourful giant clam species. In this study, T. crocea from Xisha, South China Sea was used to study mantle colour polymorphism by CSE-1 imaging and colour-measuring system and cluster analysis. Moreover, the relationship between mantle colour and morphological traits of T. crocea was also studied. The results showed that the mantle colour of most T. crocea individuals was distributed in the blue and red primary regions, and only a few individuals showed colour distribution in the green primary and bright green regions. T. crocea were clustered into six colour groups (including brown, reddish brown, light blue, dark blue, green and yellow), and the colour differences between each group were >15, among which the difference between dark blue colour of the fourth type and yellow colour of the sixth type was the largest (E=74.68), while the difference between light blue of the third type and dark blue of the fourth type was the smallest (E=18.98). The L, a, and b values of T. crocea mantle had significant positive correlations with shell height (P<0.05); the correlation coefficients were 0.2080, 0.2210, and 0.2375, respectively. This study provided a basic reference for the conservation of giant clam resources and the recovery of coral reef ecosystems.