A large population of adult colonies will be tagged at the study site to capture a wide range of phenotypic responses to thermal stress. These corals will be used to examine the relationship between thermotolerance and two key fitness traits: growth and fecundity. Corals can be broadcast spawners, releasing eggs and sperm for external fertilisation, or brooders, releasing internally fertilised fully formed larvae. Corals can also be categorised, in terms of life history traits, as competitive, weedy, stress tolerant or generalist (Darling et al. 2013). Competitive and weedy species tend to have relatively fast growth rates and high structural complexity but are often more susceptible to thermal stress and disease. In contrast, stress tolerant species are often slow growing and have massive or sub massive growth forms, while generalist species may have characteristics of different life history groups (e.g., fast growth rates and high stress tolerance). Donor colonies will be selected from four species to represent contrasting life histories and reproductive strategies including one weedy brooder (Pocillopora damicornis), and three broadcast spawning species representing generalist (e.g., Merulina spp.), stress tolerant (e.g., Favites spp.) and competitive (Acropora spp.) life histories. Certain coral species, including P. damicornis and some Acropora species (e.g., A. millepora, A. hyacinthus) have well described and annotated genomic information and are therefore considered model species for coral genomics (Kortschak et al. 2003; Shinzato et al. 2011; Traylor-Knowles et al. 2011). For each species at least 100 colonies will be permanently tagged at the study site to capture a high proportion of phenotypic variation within each population. Growth rates and fecundity will be estimated in each individual in parallel with examinations of individual differences in thermotolerance. The location of each adult colony will be mapped using GPS. Colonies of similar size (age) will be selected and colonies will be far enough apart (at least 10 m) to reduce the chance of sampling clones. Growth rates will be measured in situ using the buoyant weight technique. Fecundity will be estimated by removing 3 small branches or fragments from colonies just prior to spawning, fixing, decalcifying and counting the number and size of eggs in 10 polyps per fragment directly or using histological techniques for species with small eggs. Measurements of thermotolerance will be carried out on coral nubbins (a nubbin is defined as a small branch or fragment 3-5 cm in length that can be removed without causing harm to the donor colony) excised from each donor colony. At least five nubbins will be exciseded from each colony and randomly assigned to several experimental flow-through seawater tanks. This will result in a total of 2000 nubbins from four species and 100 genotypes per species. Nubbins will be kept in an in situ nursery at the same depth and habitat as the tagged colonies for approximately one week to recover from the stress of fragmentation. Experiments will be carried out during the warmest month of the year (based on a local decadal climatology). Temperature in the experimental tanks will be maintained at ambient for 1 week, then raised gradually above known local bleaching thresholds and maintained there for a realistic period of time to mimic the duration of natural thermal bleaching events, before being gradually returned to ambient temperature. The response to thermal stress will be measured by recording the proportion of nubbins bleaching and dying during the experiment. This approach differs from many previous experiments which have focused on short intense stressors and on bleaching rather than mortality as a response (Fitt et al. 2009). Changes in photochemical efficiency before, during and after thermal stress (for surviving nubbins), will also be estimated using an underwater Pulse Amplitude Modulator (Diving PAM) to provide an additional measure of thermotolerance. The hypothesis to be tested is: are there are resource trade- offs between increased thermotolerance, growth rates and fecundity within populations and among species with contrasting life histories? Each trait will be tested individually using linear mixed modelling approaches with species as a fixed factor. The overall aim of the experiment is to see if resource trade-offs exist, however, this experiment will also identify whether there are exceptions to the rule for certain individuals (i.e., “super corals” that resist thermal stress while maintaining high growth rates and fecundity).

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