The Importance of the Rare: The Role of Background Symbiodinium in the Response of Reef Corals to Environmental Change

摘要: of a dissertation at the University Miami. Dissertation supervised by Associate Professor Andrew C. Baker. No. pages in text. (173) Reef ecosystems throughout much tropics are predicted to decline coral cover and diversity as result ongoing climate change (ocean acidification, temperature increases, sea level rise), disease, pollution, overfishing. Corals may be able respond some these stressors associating with diverse algal symbionts (Symbiodinium spp.) which vary their physiological traits therefore expand corals’ realized niche space. This used high-sensitivity molecular techniques investigate presence functional role ‘background’ or ‘rare’ Symbiodinium, occur low abundance, not detected using standard methods. First, order determine prevalence mixed-clade symbiont communities (including potentially low-abundance populations), I highly-sensitive, real-time PCR assay analyze archived DNA from collection geographically phylogenetically corals. found that Symbiodinium were common, clades C D present all 39 species examined. These findings provide strong evidence no is restricted hosting only single type. then investigated through series bleaching recovery experiments involving Caribbean Montastraea cavernosa. monitored changes community structure newly-designed quantitative assays, function chlorophyll fluorometry. hosted clade before (except for 2 139 cores trace amounts well). All bleached colonies (both herbicide-bleached heat-bleached) recovered dominant both 24C 29C temperatures. Therefore, (or even undetectable) became corals after disturbance. Increased temperatures, without acute disturbance, underwent less-dramatic, slower changes. bleached, but exposed heat either during recovery, fewer D1a than acclimated higher During third experiment, same how clade, past thermal history, host genotype, affect thermotolerance second stress exposure. that, stress, previously-bleached lost exhibited less photochemical damage C3 symbionts. Prior exposure, did increase thermotolerance, unless it was also associated shifts D1a-dominance. demonstrates rare undetectable symbionts) can become dominant, eventually play critical response. Finally, two-part experiment effect incremental warming cooling on incrementally heated 33C had efficiency containing symbionts, experienced loss. cooling, however, equal to, lower C3. Despite this, still compared suggests loss decoupled one another generally more resistant expulsion, regardless performance hospite. study shows M. cavernosa niches wider reinforcing importance redundancy dynamic environments. Together, studies show mixed resistance resilience have indicate potential allow reef rapidly adapt acclimatize environmental change.