Low symbiont diversity in southern Great Barrier Reef corals, relative to those of the Caribbean

Abstract

The specific identity of endosymbiotic dinoflagellates (Symbiodinium spp.) from most zooxanthellate corals is unknown. In a survey of symbiotic cnidarians from the southern Great Barrier Reef (GBR), 23 symbiont types were identified from 86 host species representing 40 genera. A majority (Ͼ85%) of these symbionts belong to a single phylogenetic clade or subgenus (''C'') composed of closely related (as assessed by sequence data from the internal transcribed spacer region and the ribosomal large subunit gene), yet ecologically and physiologically distinct, types. A few prevalent symbiont types, or generalists, dominate the coral community of the southern GBR, whereas many rare and/or specific symbionts, or specialists, are found uniquely within certain host taxa. The comparison of symbiont diversity between southern GBR and Caribbean reefs shows an inverse relationship between coral diversity and symbiont diversity, perhaps as a consequence of more-rapid diversification of Caribbean symbionts. Among clade C types, generalists C1 and C3 are common to both Caribbean and southern GBR symbiont assemblages, whereas the rest are regionally endemic. Possibly because of environmental changes in the Caribbean after geographic isolation through the Quaternary period, a high proportion of Caribbean fauna associate with symbiont taxa from two other distantly related Symbiodinium clades (A and B) that rarely occur in Pacific hosts. The resilience of Porites spp. and the resistance of Montipora digitata to thermal stress and bleaching are partially explained by their association with a thermally tolerant symbiont type, whereas the indiscriminant widespread bleaching and death among certain Pacific corals, during El Niño Southern Oscillation events, are influenced by associations with symbionts possessing higher sensitivity to thermal stress.Cnidarians such as hard corals, soft corals, sea fans, and anemones are the principal faunal constituents of benthic AcknowledgmentsWe thank Jill Torregiani, María del Carmen Gómez-Cabrera, Paul Fisher, and Michael Stat for assisting with the collection and processing of samples, as well as M. J. Van Oppen for her help with determining the specific identity of subclades C1, C2, and C3 (Van Oppen et al. 2001).

Novel algal symbiont (Symbiodinium spp.) diversity in reef corals of Western Australia

“…LaJeunesse et al 2004a) and studies done on the host species sampled in the present study throughout the Indo-Pacific (e.g. Loh et al 2001, LaJeunesse et al 2003, 2004b, 2010a, Chen et al 2005, McClanahan et al 2005. The symbiont type C1h harbored by most of the Pocillopora damicornis sampled in the present study, for example, was also the most common symbiont in these corals sampled from Zanzibar, Tanzania, in the Western Indian Ocean (LaJeunesse et al 2010a), indicating that some of the partner combinations found in Western Australia occur in other regions of the Indian Ocean.…”

“…In previous studies, C40 occurred in several scleractinian genera from the central Great Barrier Reef (GBR), but was absent from coral populations in the cooler and more seasonably variable southern GBR (LaJeunesse et al 2003(LaJeunesse et al , 2004a. The restricted sampling of coral diversity and low sample sizes in the present survey limit our ability to draw broad conclusions about the importance of temperature in restricting the range of these symbionts.…”

“…Regardless of whether some variation within the Symbiodinium ITS-2 is actually intra-specific (rather than species-level), it is widely agreed that the clade-level is too coarse for generalizations regarding the ecological and physiological attributes of Symbiodinium (Iglesias-Prieto & Trench 1997a,b, Savage et al 2002, LaJeunesse et al 2003, 2004b, Iglesias-Prieto et al 2004, Tchernov et al 2004, Warner et al 2006, Sampayo et al 2007, Thornhill et al 2008.…”

Corals from the Persian/Arabian Gulf as models for thermotolerant reef-builders: Prevalence of clade C3 Symbiodinium, host fluorescence and ex situ temperature tolerance

“…This type has been suggested as contributing to the resistance of Porites spp. to temperature anomalies (LaJeunesse et al, 2003) and it is the characteristic symbiont found in Porites from the Pacific and Indo-Pacific (Lajeunesse, 2005;Barshis et al, 2010). Noteworthily, C15 contributed almost 95% of the sequences isolated from 31 colonies of P. lobata from American Samoa (Barshis et al, 2010).…”

“…Further sampling would help discern the spatial and temporal distribution of symbionts in the Gulf. The prevalence of Symbiodinium C3 in Abu Dhabi corals is surprising, given that this type is considered a ''generalist'' on Indo-Pacific reefs (LaJeunesse et al, 2003). The fact that Abu Dhabi corals routinely experience summer temperature of up to 36°C (Foster et al, 2012) indicates that this Symbiondinium clade can also support symbiotic associations with an exceptional thermotolerance.…”