[futrtrubl]

I presume you've seen these papers...
SCHOENBERG D.A. & R.K. TRENCH (1980) Genetic variation in Symbiodinium (=Gymnodinium) microadriaticum Freudenthal, and specificity in its symbiosis with marine invertebrates: I. Isoenzyme and soluble protein patterns of axenic cultures of S. microadriaticum. Proc. R. Soc. Lond. B. 207: 405-427.

SCHOENBERG D.A. & R.K. TRENCH (1980) Genetic variation in Symbiodinium (=Gymnodinium) microadriaticum Freudenthal, and specificity in its symbiosis with marine invertebrates: II. Morphological variation in S. microadriaticum. Proc. R. Soc. Lond. B. 207: 429-444.

SCHOENBERG D.A. & R.K. TRENCH (1980) Genetic variation in Symbiodinium (=Gymnodinium) microadriaticum Freudenthal, and specificity in its symbiosis with marine invertebrates: III. Specificity and infectivity of S. microadriaticum. Proc. R. Soc. Lond. B 207: 445-460.

Also I have seen a paper that claims while corals show some specificity, it's usually to a cell size rather than a species. I can't remember now the name or author of the paper.

Edward