Symbiodinium diversity in mesophotic coral communities on the Great Barrier Reef: a first assessment

Abstract

Despite a growing interest in mesophotic coral ecosystems (MCEs), information on the photosynthetic endosymbionts (genus Symbiodinium) associated with scleractinian corals inhabiting deep reef ecosystems is sparse. Here, the deep-water Symbiodinium diversity is assessed from 10 different coral genera at a depth range of 45 to 70 m on the Great Barrier Reef (GBR), Australia. Symbiodinium identity was established using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the internal transcribed spacer region 2 (ITS2) of the ribosomal DNA. Except for the novel Symbiodinium type C131 (found in Porites), all Symbiodinium types have previously been identified in shallow reef corals across the Pacific. Specimens of Seriatopora, Montipora, and Porites harboured similar symbionts as reported in shallow water (e.g. C3n, C3n-hh, C15, and C17), thus adhering to patterns of host-specificity across a wide depth range. However, several other Symbiodinium types were found to transcend previously established patterns of host-specificity at mesophotic depths. For example, 'host-specialist' types C3i and C3k (previously only reported in Acropora spp.) were found here to associate with a range of different genera (Leptoseris, Pachyseris, Fungia, and Echinophyllia). Although limited in sample size, this preliminary survey indicates that mesophotic habitats on the GBR may not represent an isolated community in terms of Symbiodinium diversity, which has significant relevance to their potential to act as refugia. Moreover, the present study identifies the need to examine symbiont diversity across broad environmental ranges (including MCEs) in order to gain an accurate understanding of symbiosis specificity and distribution range of specific coral-Symbiodinium associations. KEY WORDS: Symbiodinium · Mesophotic · Deep reefs · Coral · ITS2 · DGGE · Great Barrier ReefResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 439: 117-126, 2011 118 zation of Symbiodinium into cladal (e.g. Rowan & Powers 1991, Baker & Rowan 1997 and subcladal types (e.g. van Oppen et al. 2001, LaJeunesse 2002 has greatly enhanced our understanding of the symbiosis. Studies of Symbiodinium diversity on broad latitudinal or longitudinal gradients have shown distinct biogeographical patterns (e.g. LaJeunesse et al. 2003, Silverstein et al. 2011), whereas more local or species-specific studies have highlighted ecological zonation, physiological diversification, and host-specificity of distinct symbionts (e.g. Rowan & Knowlton 1995, LaJeunesse et al. 2003, 2004, Iglesias-Prieto et al. 2004, Sampayo et al. 2007, Frade et al. 2008a.Community-wide shifts in symbiont diversity occur with increasing depth (LaJeunesse 2002, LaJeunesse et al. 2003, 2004, but this observation is likely to be, in part, the result of host community composition changes over depth. Nonetheless, studies focusing on single coral species show a similar pattern, and depth zonation of symbionts has been shown to occur on a cladal...

Mesophotic coral depth acclimatization is a function of host-specific symbiont physiology

“…Coral-Symbiodinium association on the upward-facing surface of the colonies followed a host-specific rather than a depth-specific pattern supporting data from the Great Barrier Reef (Bongaerts et al, 2011) and the Caribbean (Bongaerts et al, 2013). Although one species of Leptoseris hosted clade D symbionts in shallow water and other corals of this genus were associated with clade C symbionts in deep water, there was no symbiont species overlap between depths, and hence we could not identify depthdependent shifts of the main Symbiodinium types as reported for other coral species (Frade et al, 2008b;Lesser et al, 2010;Cooper et al, 2011).…”

To what extent do mesophotic coral ecosystems and shallow reefs share species of conservation interest?

“…Kahng et al [2] reported 26 papers from 16 regions in their 2010 review of MCEs for zooxanthellate corals, as well as papers on fish and algae. Additional data are now available from: the Red Sea [12,13], the Caribbean [14,15], the central Pacific [16][17][18], the Great Barrier Reef [19,20], and others. However, the techniques employed, the questions asked and the taxa considered are variable.…”

Habitat-specific environmental conditions primarily control the microbiomes of the coral Seriatopora hystrix

“…The genus Symbiodinium can be categorised into eight distinct phylogenetic clades (A-H) based on their ribosomal DNA sequence (ITS2), with five of these (A-D and F) found in association with the corals (Baker, 2003). A high degree of host specificity (LaJeunesse et al, 2004(LaJeunesse et al, , 2010, habitat partitioning and ecological diversification have been identified as controlling factors of the distribution of the different Symbiodinium clades (Douglas, 1998;LaJeunesse et al, 2003;LaJeunesse, 2005;Stat et al, 2008a;Bongaerts et al, 2010Bongaerts et al, , 2011bLaJeunesse et al, 2010;Silverstein et al, 2011). To date the main role of Symbiodinium in the coral holobiont is thought to be through its involvement in its host's metabolism, including photosynthesis and nutrient cycling, which provides their hosts with up to 95% of their carbon requirements (Muscatine and Porter, 1977) and the cycling of nitrogenous compounds (Leggat et al, 2007;Pernice et al, 2012).…”