Persistence of non-caribbean algal symbionts in Indo-Pacific mushroom corals released to Jamaica 35 years ago

Mushroom corals endemic to the Indo-Pacific were collected and brought to Discovery Bay, Jamaica, and released on the fore-reef in the mid to late 1960’s by Thomas F. Goreau, an early pioneer in coral research (cf. Goreau et al. 1969 p 180; R. K. Trench, personal communication). Subsequently, the potential problems arising from introduction of an exotic species to the Caribbean were realized. Several attempts to eradicate these non-Caribbean species were then made between 1970 and 1980 and more than 25 adult individuals were removed (cf. Bush et al. 2004; J. Woodley, personal communication). However, re-discovery of two Fungia scutaria individuals in March of 2003 showed that a remnant population of this particular mushroom coral has persisted for over 35 years in the Caribbean (Bush et al. 2004). Since being introduced to Atlantic waters, these corals have displayed remarkable resilience, enduring two destructive hurricanes (Woodley 1992), environmental degradation resulting in collapse of native coral populations (Hughes 1994), and several bleaching events related to thermal stress (Goreau 1990). Understanding the stability and/or flexibility of coralalgal symbioses is of great interest to those concerned with the long-term effects of climate change on reef building corals (Baker 2003). Whether the original symbiont population of F. scutaria was replaced by one of the many local Symbiodinium spp. found in the Caribbean (LaJeunesse 2002; LaJeunesse et al. 2003) is addressed in this report through use of genetic analyses. Tissue from a F. scutaria collected on the fore-reef (15 m) off the north shore of Jamaica was preserved in 95% ethanol, homogenized, and the DNA isolated as described previously (LaJeunesse et al. 2003). PCRdenaturing gradient gel electrophoresis (DGGE) fingerprinting of the ribosomal internal transcribed spacer region (ITS) 2 was performed and the two lowest and most prominent DNA bands were excised and sequenced (Fig. 1). The genome of this Symbiodinium sp. contains two co-dominant sequence variants of the ITS 2. They appear to reflect a phylogenetic transition from C1 (ancestral) to the C1b (derived) sequence. When the DGGE fingerprints and sequences are compared with data from hundreds of Caribbean and Indo-Pacific host taxa, an identical match is made with a symbiont of Pacific origin, type C1b (Fig. 1). That member of Symbiodinium clade C was recently identified in the coral Pavona varians (collected at 3 m) from the southern Great Barrier Reef (GBR) (LaJeunesse et al. 2003) and in Leptastrea purpurea (15 m) and the organ pipe octocoral, Tubipora musica (15 m), from mid-shelf reefs on the central GBR (LaJeunesse et al., in press). It is also found in P. superficialis (6 m) from the Pacific coast of Panama (A.C. Baker and T.C. LaJeunesse, unpublished data) and appears to possess a wide, albeit uncommon, geographic distribution in the Pacific. The identical match of the ITS 2 fingerprint, C1b, from the Jamaican F. scutaria to samples taken from various Pacific hosts indicates that this Symbiodinium sp. is most probably a product of the Indo-Pacific diversification of clade C. Presently, over 50 genetically distinguishable symbiont types, mostly from Symbiodinium clades B and C, have been classified from extensive host collections at several sites in the Caribbean (LaJeunesse 2002; LaJeunesse, in press). They predominantly have limited geographic, host-specific and/or well-defined depth distributions within the Caribbean Sea. Only two types from clade C, namely C1 (S. goreaui) and C3, are known to also occur within a wide diversity of host taxa T. C. LaJeunesse (&) Department of Plant Biology and Institute of Ecology, University of Georgia, Plant Sciences Building, Athens, GA 30602, USA E-mail: lajeunes@fiu.edu Tel.: +1-305-3481317 Fax: +1-305-3481986