Non-seasonal clade-specificity and subclade microvariation in symbiotic dinoflagellates (Symbiodinium spp.) in Zoanthus sansibaricus (Anthozoa: Hexacorallia) at Kagoshima Bay, Japan

While much work has investigated the genetic diversity of symbiotic dinoflagellate genus Symbiodinium Freudenthal in cnidarians, investigations into such diversity over temporal scales (seasonal and/or annual) remain scarce. Here, we have sequenced the internal transcribed spacer of ribosomal DNA (ITS‐rDNA) of Symbiodinium from samples of designated Zoanthus sansibaricus Carlgren (Anthozoa: Hexacorallia) colonies collected for 12 months (August 2004–July 2005) at a high latitude non‐reefal coral community at Sakurajima, Kagoshima Bay, Japan (31°35′N, 130°35′E). Our results show that despite large ocean temperature changes (15.0–29.0°C) throughout the one‐year experimental period, Z. sansibaricus colonies contained only clade C Symbiodinium from many different subclade C1/C3‐related novel types not previously reported. While no temporal changes in clade‐level associations were seen, there were consistent and extremely large amounts (145 unique sequences out of 153 total obtained sequences) of genotypic microvariation observed in our obtained sequences. Despite Z. sansibaricus acquiring Symbiodinium horizontally and the presence of various other Symbiodinium clades (A, G) and subclades (e.g. C15 and derived subclades) in the immediate environment, Z. sansibaricus at Sakurajima specifically associates with subclade C1/C3‐related Symbiodinium. While subclades C1/C3 have been found in a variety of different environments and are believed to be ancestral, ‘generalist’ types of Symbiodinium, C1/C3‐related clades such as seen here may be more adapted to specialized niches. We theorize that specific and year‐round association with many different types of subclade C1/C3‐related Symbiodinium helps Z. sansibaricus to survive in the fluctuating Sakurajima environment.