MEPS 195:93-100 (2000)  -  doi:10.3354/meps195093

Diversity of dinoflagellate symbionts (zooxanthellae) in a host individual

Alvin A. Carlos1, Brett K. Baillie2, Tadashi Maruyama2,*

1Marine Science Institute, College of Science, University of the Philippines, Diliman, Quezon City 1101, Philippines
2Marine Biotechnology Institute, Kamaishi Laboratories, Heita 3-75-1, Kamaishi, Iwate 026-0001, Japan
*Corresponding author. E-mail:

ABSTRACT: Zooxanthellae are phototrophic dinoflagellates that exist in symbiosis with a variety of marine invertebrates. The traditional view of zooxanthella-invertebrate symbioses suggests that individual hosts harbor taxonomically homogeneous symbiont populations. To assess the diversity of the zooxanthella assemblage inhabiting an individual host, zooxanthellae from 6 species of clam (Tridacna gigas, T. squamosa, T. crocea, Hippopus hippopus, H. porcellanus and Corculum cardissa) and 1 species of sea anemone (Aiptasia sp.) were studied using temperature-gradient gel electrophoresis (TGGE), coupled with polymerase chain reaction (PCR) using zooxanthella-specific primers that were designed to target hypervariable regions of the small subunit ribosomal RNA (ssrRNA) gene. Results revealed that 1 clam may harbor 2 or more genotypically distinct zooxanthellae, with 1 or more dominant taxa occurring at a time. The clams studied associated with at least 4 zooxanthellar taxa. Nucleotide sequencing of the TGGE bands and phylogenetic reconstruction revealed that the zooxanthellar taxa in clams were Symbiodinium spp.; 1 was identical to previously cultured clam symbiont isolates, 1 appeared identical to a previously studied unculturable clam symbiont, and the other 2 clams represented novel strains of Symbiodinium. Individual Aiptasia sp. harbored only 1 zooxanthellar taxon, which had a ssrRNA sequence identical to that of S. pulchrorum, previously isolated from Aiptasia pulchella. This study has shown that individual tridacnid and cardiid clams can harbor heterogeneous zooxanthellae.


KEY WORDS: Zooxanthellae · Diversity · Temperature-gradient gel electrophoresis · Dinoflagellates · Clams


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