*2.1. Carotenoids of Corals and the Tridacnid Clam*

The carotenoids composition of the corals and the tridacnid clam were similar to each other (Table 1). Ά,Ά-Carotene, peridinin (including the 9<sup>ȝ</sup>*Z* isomer), pyrrhoxanthin, diatoxanthin, and diadinoxanthin were found in these animals. These carotenoid patterns resembled those of symbiotic zooxanthellae [5,6]. The results indicate that corals and the tridacnid clam directly absorb carotenoids from symbiotic zooxanthellae and accumulate them without metabolic modification. In the eggs of corals, peridinin and pyrroxanthin were present as major carotenoids. It was assumed that peridinin and pyrroxanthin play important roles in reproduction in corals, as with astaxanthin in salmonid fishes [7]. 

Recently, Daigo *et al.* studied carotenoids of more than 20 species of coral inhabiting reefs in Okinawa [8]. They reported that carotenoids found in these corals were not only peridinin and diadinoxanthin, that originated from symbiotic zooxanthellae, but also zeaxanthin, lutein, and, fucoxanthin, that originated from cyanobacteria, green algae, and diatoms. Cyanobacteria, green algae, and diatoms were epizoic and/or endolithic algae that grew in association with the corals. Corals accumulated carotenoids from these epizoic and/or endolithic algae [8]. However, the present study found that carotenoids in *Acropora* corals, inhabiting the Kuroshio current coast of Kochi, only consisted of those that originated from zooxanthellae. These differences might reflect the constitution of associating algae with corals. 

Peridinin and pyrrhoxanthin were found to be major carotenoids in the tridacnid clam. In general, major carotenoids found in clams are fucoxanthin and its metabolites originating from diatoms [9–11]. On the other hand, neither fucoxanthin nor its metabolites were found in the tridacnid clam. This indicates that the tridacnid clam only ingested carotenoids from dinoflagellate algae. Similar results were reported in carotenoids of the bivalves, *Modiolus modiolus* and *Pecten maximus* [12]. 

**Figure 1.** Carotenoids identified from *Acropora* corals, the tridacnid clam *T. squamosa*, starfish *A. planci*, and sea snail *D. fragum*. 


**Table 1.** Carotenoids of *Acropora* corals and the tridacnid clam *Tridacna* 

*squamosa*.
