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1. Measuring Coral Skeletal Architecture Using Image Analysis

   https://doi.org/10.17504/protocols.io.bx5bpq2n  

   McLachlan, RH; Patel, A; Grottoli, AG (January 2021, Protocolsio)

   Coral morphology is influenced by genetics, the environment, or the interaction of both, and thus is highly variable. This protocol outlines a non-destructive and relatively simple method for measuring Scleractinian coral subcorallite skeletal structures (such as the septa length, theca thickness, and corallite diameter, etc.) using digital images produced as a result of digital microscopy or from scanning electron microscopy. This method uses X and Y coordinates of points placed onto photomicrographs to automatically calculate the length and/or diameter of a variety of sub-corallite skeletal structures in the Scleractinian coral Porites lobata. However, this protocol can be easily adapted for other coral species - the only difference may be the specific skeletal structures that are measured (for example, not all coral species have a pronounced columella or pali, or even circular corallites). This protocol is adapted from the methods described in Forsman et al. (2015) & Tisthammer et al. (2018). There are 4 steps to this protocol: 1) Removal of Organic Tissue from Coral Skeletons 2) Imaging of Coral Skeletons 3) Photomicrograph Image Analysis 4) Calculation of Corallite Microstructure Size dx.doi.org/10.17504/protocols.io.bx5bpq2n 

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2. Image capture and pre-filtering for 3D photogrammetry of coral colonies

   https://doi.org/10.17504/protocols.io.bgdcjs2w  

   Million, W; Kenkel, C (July 2020, Protocolsio)

   null (Ed.)

   This is a protocol for generating images to be used in 3D model building via Agisoft Metashape for coral photogrametry. This will cover underwater, field-based methods and tips to collect photographs and preprocessing of photos to improve model building. Image capture is the most important part of 3D photogrammetry because the photos taken at this point will be all that you'll have to build models and collect data. As such, you want to ensure you have enough photos to work with in the future so, in general, more is better. That being said, too many blurry or out of focus pictures will hamper model building. You can optimize your time in the field by taking enough photos from the appropriate angles, however efficiency will come with practice. This is the protocol developed and used by the Kenkel lab to phenotype Acropora cervicornis colonies as part of field operations in the Florida Keys. We incorporate Agisoft Metashape markers in this workflow to scale models and improved model building. The scaling objects used by the Kenkel lab are custom-made, adjustable PVC arrays that include unique markers and bleaching color cards, affectionately called the "Tomahawk". Specs for building a Tomahawk are included in this protocol. Filtering and pre-processing of photos is not always necessary but can be used to salvage 3D models that would be otherwise blurry or incomplete. Here, we describe photo editing in Adobe Lightroom to adjust several characteristics of hundreds of images simultaneously. For a walkthrough and scripts to run Agisoft Metashape on the command line, see https://github.com/wyattmillion/Coral3DPhotogram. For directions to phenotype coral from 3D models see our Phenotyping in MeshLab protocol. These protocols, while created for branching coral, can be applied to 3D models of any coral morphology or any object really. Our goal is to make easy-to-use protocols using accessible softwares in the hopes of creating a standardized method for 3D photogrammetry in coral biology. DOI dx.doi.org/10.17504/protocols.io.bgdcjs2w 

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3. Corals survive severe bleaching event in refuges related to taxa, colony size, and water depth

   https://doi.org/10.1038/s41598-024-58980-1  

   Winslow, Erin M.; Speare, Kelly E.; Adam, Thomas C.; Burkepile, Deron E.; Hench, James L.; Lenihan, Hunter S. (April 2024, Scientific Reports)

   Abstract Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera,PocilloporaandAcropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, butAcroporableached more severely thanPocilloporaoverall. Acroporableached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching inPocilloporacorals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10–29 cm) or small colonies (5–9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality. 

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4. A global coral-bleaching database, 1980–2020

   https://doi.org/10.1038/s41597-022-01121-y  

   van Woesik, Robert; Kratochwill, Chelsey (January 2022, Scientific Data)

   Abstract Coral reefs are the world’s most diverse marine ecosystems that provide resources and services that benefit millions of people globally. Yet, coral reefs have recently experienced an increase in the frequency and intensity of thermal-stress events that are causing coral bleaching. Coral bleaching is a result of the breakdown of the symbiosis between corals and their symbiotic microalgae, causing the loss of pigments and symbionts, giving corals a pale, bleached appearance. Bleaching can be temporary or fatal for corals, depending on the species, the geographic location, historical conditions, and on local and regional influences. Indeed, marine heat waves are the greatest threat to corals worldwide. Here we compile a Global Coral-Bleaching Database (GCBD) that encompasses 34,846 coral bleaching records from 14,405 sites in 93 countries, from 1980–2020. The GCBD provides vital information on the presence or absence of coral bleaching along with site exposure, distance to land, mean turbidity, cyclone frequency, and a suite of sea-surface temperature metrics at the times of survey. 

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5. Farmerfish gardens help buffer stony corals against marine heat waves

   https://doi.org/10.1371/journal.pone.0282572  

   Honeycutt, Randi N.; Holbrook, Sally J.; Brooks, Andrew J.; Schmitt, Russell J. (March 2023, PLOS ONE)

   Melzner, Frank (Ed.)

   With marine heat waves increasing in intensity and frequency due to climate change, it is important to understand how thermal disturbances will alter coral reef ecosystems since stony corals are highly susceptible to mortality from thermally-induced, mass bleaching events. In Moorea, French Polynesia, we evaluated the response and fate of coral following a major thermal stress event in 2019 that caused a substantial amount of branching coral (predominantly Pocillopora ) to bleach and die. We investigated whether Pocillopora colonies that occurred within territorial gardens protected by the farmerfish Stegastes nigricans were less susceptible to or survived bleaching better than Pocillopora on adjacent, undefended substrate. Bleaching prevalence (proportion of the sampled colonies affected) and severity (proportion of a colony’s tissue that bleached), which were quantified for >1,100 colonies shortly after they bleached, did not differ between colonies within or outside of defended gardens. By contrast, the fates of 399 focal colonies followed for one year revealed that a bleached coral within a garden was a third less likely to suffer complete colony death and about twice as likely to recover to its pre-bleaching cover of living tissue compared to Pocillopora outside of a farmerfish garden. Our findings indicate that while residing in a farmerfish garden may not reduce the bleaching susceptibility of a coral to thermal stress, it does help buffer a bleached coral against severe outcomes. This oasis effect of farmerfish gardens, where survival and recovery of thermally-damaged corals are enhanced, is another mechanism that helps explain why large Pocillopora colonies are disproportionately more abundant in farmerfish territories than elsewhere in the lagoons of Moorea, despite gardens being relatively uncommon. As such, some farmerfishes may have an increasingly important role in maintaining the resilience of branching corals as the frequency and intensity of marine heat waves continue to increase. 

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