CORRESPONDENCE BETWEEN COLD TOLERANCE AND TEMPERATE BIOGEOGRAPHY IN A WESTERN ATLANTIC SYMBIODINIUM (DINOPHYTA) LINEAGE¹

Abstract

Many corals form obligate symbioses with photosynthetic dinoflagellates of the genus Symbiodinium Freudenthal (1962). These symbionts vary genotypically, with their geographical distribution and abundance dependent upon host specificity and tolerance to temperature and light variation. Despite the importance of these mutualistic relationships, the physiology and ecology of Symbiodinium spp. remain poorly characterized. Here, we report that rDNA internal transcribed spacer region 2 (ITS2) defined Symbiodinium type B2 associates with the cnidarian hosts Astrangia poculata and Oculina arbuscula from northerly habitats of the western Atlantic. Using pulse-amplitude-modulated (PAM) fluorometry, we compared maximum photochemical efficiency of PSII of type B2 to that of common tropical Symbiodinium lineages (types A3, B1, and C2) under cold-stress conditions. Symbiont cultures were gradually cooled from 26°C to 10°C to simulate seasonal temperature declines. Cold stress decreased the maximum photochemical efficiency of PSII and likely the photosynthetic potential for all Symbiodinium clades tested. Cultures were then maintained at 10°C for a 2-week period and gradually returned to initial conditions. Subsequent to low temperature stress, only type B2 displayed rapid and full recovery of PSII photochemical efficiency, whereas other symbiont phylotypes remained nonfunctional. These findings indicate that the distribution and abundance of Symbiodinium spp., and by extension their cnidarian hosts, in temperate climates correspond significantly with the photosynthetic cold tolerance of these symbiotic algae.

The influence of irradiance on tolerance to high and low temperature stress exhibited by Symbiodinium in the coral, Pocillopora damicornis, from the high‐latitude reef of Lord Howe Island

“…It is well-documented that decreased temperatures intensify photo-inhibition in higher plants (Smilie et al 1988) due to a reduction in the rate at which the quenching of PSII occurs (Krause 1992). However, few studies have documented the effect of cold temperature stress on corals, despite knowledge of increased temperatures causing a breakdown of the symbiotic relationship (Lesser 1996;Thornhill et al 2006).…”

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

“…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.…”

“…Rodriguez-Lanetty et al 2001, Savage et al 2002, Macdonald et al 2008, Thornhill et al 2008) and in isolated locations (e.g. LaJeunesse et al 2004a) and studies done on the host species sampled in the present study throughout the Indo-Pacific (e.g.…”

“…B2) appear to be adapted to cooler temperate environments with greater seasonal fluctuations in temperature and irradiance (e.g. Thornhill et al 2008).…”

“…LaJeunesse 2002). Studies have shown that functional traits can differ among symbiont types both in hospite and in culture, particularly with respect to their temperature optima (Iglesias-Prieto et al 1992, Warner et al 1999Thornhill et al 2008, Hennige et al 2009), response to thermal stress, and influence on the relative bleaching susceptibility/ resistance of their scleractinian hosts , Glynn et al 2001, Rowan 2004, Goulet et al 2005, Berkelmans & van Oppen 2006, Jones et al 2008, LaJeunesse et al 2010b.…”