Loss of Symbiodinium from bleached Australian scleractinian corals (Acropora hyacinthus, Favites complanata and Porites solida)

Abstract

Coral bleaching results from the dissociation of Symbiodinium and is primarily related to sea surface temperatures above mean yearly maximums. The numbers of live, dead, and mitotic Symbiodinium cells lost from three scleractinian corals from three different families (Acropora hyacinthus, Favites complanata, and Porites solida), which have not been studied previously in central Queensland (Australia), were compared at 28, 30, 32, and 34°C. Specific expulsion rates, growth rates, and mitotic indices were compared for each host at each temperature. Porites solida was the most robust coral, A. hyacinthus bleached more readily at low temperatures and F. complanata showed levels of intermediate bleaching tolerance to elevated temperatures. However, the timing of Symbiodinium cell loss was similar between all corals tested. Mitotic indices and specific growth rates were found to be positively associated with increasing temperature; thus, symbiont reproduction increased despite elevated losses of Symbiodinium from the host. Because all corals in the present study were symbiotic with Symbiodinium from clade C, different levels of stress tolerance to temperature suggests that bleaching resistance is an attribute associated with the coral host and, to a lesser degree, the symbiont.

Breakdown of the coral-algae symbiosis: towards formalising a linkage between warm-water bleaching thresholds and the growth rate of the intracellular zooxanthellae

“…Bhagooli and Hidaka (2002) found that the intracellular MI of zooxanthellae within the coral Galaxea fasicularis increased with temperature, and was maximal at the observed bleaching threshold temperature of 30 • C. The authors concluded that, "the host appeared to lose the capacity of controlling algal cell division after 7-day exposure to 30 • C". A positive association between rising temperature, zooxanthellae MI, and coral bleaching was also recorded by Strychar et al (2004) for three different coral families (Acropora hyacinthus, Favites complanata and Porites solida). Porites solida (massive morphology) was the most thermally tolerant coral, A. hyacinthus (branching/plate morphology) bleached most readily at low temperatures, and F. Complanata (mounding morphology) showed intermediate bleaching tolerance to elevated temperature (Fig.…”

“…5a), with the different zooxanthellae types varying in terms of thermal growth optimum (Sakami, 2000;Kinzie et al, 2001;Strychar et al, 2004). Significantly, the thermal growth optimum for many of the zooxanthellae types that associate with corals often exceeds the thermal break-point of the symbiotic association (> 32 • C) (see e.g.…”

“…Significantly, the thermal growth optimum for many of the zooxanthellae types that associate with corals often exceeds the thermal break-point of the symbiotic association (> 32 • C) (see e.g. Kinzie et al, 2001;Strychar et al, 2004). Yet, this temperature-dependent ("potential") growth rate can only be obtained when essential nutrients (particularly nitrogen) are not limiting to cell multiplication (Fitt, 2000).…”

“…The implications of this suggestion are intriguing, since it implies that in natural settings, the onset of the bleaching syndrome and setting of upper thermal bleaching limits are emergent attributes of the coral symbiosis that are ultimately underpinned by the characteristic growth profile of the intracellular zooxanthellae; with excessive (re)growth potential equating with reduced thermotolerance. Since zooxanthellae growth rates have been extensively measured, and are known to display consistent variations depending not just on temperature (Kinzie et al, 2001;Strychar et al, 2004), but also external (seawater) nutrient availability (Hoegh-Guldberg, 1994;McGuire and Szmant, 1997) and Symbiodinium type (Kinzie et al, 2001;Fitt, 1985), it follows that there exists a wealth of information (at a variety of observational scales) with which to test the parsimony of the proposed bleaching linkage. The following essay provides a review of this evidence, and where possible, endeavours to provide insight into the design of future experiments that can more formally test the linkage.…”

Effects of Heat and Salinity Stress on the Sponge Cliona Celata

“…All artificial marine water was twice exposed to a sock filter (filter bag, 200 µm) before use in experimental analyses to ensure dissolution of salt in the water. Ambient lighting was simulated by a 12 h light : 12 h dark diel cycle (Mobley and Gleason, 2003) with two Super Actinic bulbs and two Actinic white bulbs following Strychar et al (2004).…”