Abstract
The unique mutualism between corals and their photosynthetic zooxanthellae (Symbiodinium spp.) is the driving force behind functional assemblages of coral reefs. However, the respective roles of hosts and Symbiodinium in this endosymbiotic association, particularly in response to environmental challenges (e.g., high sea surface temperatures), remain unsettled. One of the key obstacles is to produce and maintain aposymbiotic coral hosts for experimental purposes. In this study, a simple and gentle protocol to generate aposymbiotic coral hosts (Isopora palifera and Stylophora pistillata) was developed using repeated incubation in menthol/artificial seawater (ASW) medium under light and in ASW in darkness, which depleted more than 99% of Symbiodinium from the host within 4∼8 days. As indicated by the respiration rate, energy metabolism (by malate dehydrogenase activity), and nitrogen metabolism (by glutamate dehydrogenase activity and profiles of free amino acids), the physiological and biochemical performances of the menthol-induced aposymbiotic corals were comparable to their symbiotic counterparts without nutrient supplementation (e.g., for Stylophora) or with a nutrient supplement containing glycerol, vitamins, and a host mimic of free amino acid mixture (e.g., for Isopora). Differences in biochemical responses to menthol-induced bleaching between Stylophora and Isopora were attributed to the former digesting Symbiodinium rather than expelling the algae live as found in the latter species. Our studies showed that menthol could successfully bleach corals and provided aposymbiotic corals for further exploration of coral-alga symbioses.
Highlights
The unique mutualism between corals and their photosynthetic zooxanthellae (Symbiodinium spp.) underpins ecological success of corals in shallow and oligotrophic seawater
When I. palifera was incubated in menthol-supplemented artificial seawater (ASW), the Symbiodinium density in the coral declined with an increase in the incubation time, and rates of algal depletion were dependent on the concentration of menthol used (Fig. 1A)
In order to examine the dose response of menthol, the decline in Symbiodinium density with time was converted to an equation using a curvefitting model provided by SigmaPlot
Summary
The unique mutualism between corals and their photosynthetic zooxanthellae (Symbiodinium spp.) underpins ecological success of corals in shallow and oligotrophic seawater This association is highly vulnerable to rising seawater temperatures. Coral bleaching events are known to further cause a breakdown [1,2,3,4] or phase shift [5,6,7] in coral reefs These situations are predicted to worsen with time if the increase in seawater surface temperatures cannot be slowed [8,9]. In studies of symbionts, cultured and freshly isolated Symbiodinium (FIS) was widely used to explore the symbiont physiology Different physiological performances, such as the photosynthesis capability under thermal stress, of FIS or cultured Symbiodinium were revealed at the clade or subclade levels [13,14,15,16]. Studies on physiological responses of aposymbiotic coral hosts are limi’ted due to a lack of suitable protocols
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
