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1. Effects of corallivory and coral colony density on coral growth and survival

   https://doi.org/10.1007/s00338-021-02076-z  

   Kopecky, Kai L.; Cook, Dana T.; Schmitt, Russell J.; Stier, Adrian C. (April 2021, Coral Reefs)

   null (Ed.)

   Abstract A suite of processes drive variation in coral populations in space and time, yet our understanding of how variation in coral density affects coral performance is limited. Theory predicts that reductions in density can send coral populations into a predator pit, where concentrated corallivory maintains corals at low densities. In reality, how variation in coral density alters corallivory rates is poorly resolved. Here, we experimentally quantified the effects of corallivory and coral density on growth and survival of small colonies of the staghorn coral Acropora pulchra . Our findings suggest that coral density and corallivory have strong but independent effects on coral performance. In the presence of corallivores, corals suffered high but density-independent mortality. When corallivores were excluded, however, vertical extension rates of colonies increased with increasing densities. While we found no evidence for a predator pit, our results suggest that spatio-temporal variation in corallivore and coral densities can fundamentally alter population dynamics via strong effects on juvenile corals. 

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2. Different nitrogen sources speed recovery from corallivory and uniquely alter the microbiome of a reef-building coral

   https://doi.org/10.7717/peerj.8056  

   Rice, Mallory M.; Maher, Rebecca L.; Vega Thurber, Rebecca; Burkepile, Deron E. (January 2019, PeerJ)

   Corals are in decline worldwide due to local anthropogenic stressors, such as nutrient loading, and global stressors, such as ocean warming. Anthropogenic nutrient loading, which is often rich in nitrate, inhibits coral growth and worsens corals’ response to warming while natural sources of nitrogen, such as ammonium from fish excretion, promotes coral growth. Although the effects of nutrient loading and ocean warming have been well-studied, it remains unclear how these factors may interact with biotic processes, such as corallivory, to alter coral health and the coral microbiome. This study examined how nitrate vs. ammonium enrichment altered the effects of increased seawater temperature and simulated parrotfish corallivory on the health of Pocillopora meandrina and its microbial community. We tested the effects of nitrogen source on the response to corallivory under contrasting temperatures (control: 26 °C, warming: 29 °C) in a factorial mesocosm experiment in Moorea, French Polynesia. Corals were able to maintain growth rates despite simultaneous stressors. Seawater warming suppressed wound healing rates by nearly 66%. However, both ammonium and nitrate enrichment counteracted the effect of higher temperatures on would healing rates. Elevated seawater temperature and ammonium enrichment independently increased Symbiodiniaceae densities relative to controls, yet there was no effect of nitrate enrichment on algal symbiont densities. Microbiome variability increased with the addition of nitrate or ammonium. Moreover, microbial indicator analysis showed that Desulfovibrionaceae Operational taxonomic units (OTUs) are indicators of exclusively temperature stress while Rhodobacteraceae and Saprospiraceae OTUs were indicators of high temperature, wounding, and nitrogen enrichment. Overall, our results suggest that nitrogen source may not alter the response of the coral host to simultaneous stressors, but that the associated microbial community may be distinct depending on the source of enrichment. 

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3. Corallivory on small Porites colonies increases with coral colony size but is reduced by macroalgal associational refuge

   https://doi.org/10.1007/s00338-023-02424-1  

   Srednick, G.; Edmunds, P. J. (September 2023, Coral Reefs)

   Abstract Numerous tropical macroalgae provide associational refuge to other benthic organisms, presumably due to their physical structure and/or production of chemical metabolites. One feature determining their effectiveness as an associational refuge is likely to be the size of the organism benefitting from the refuge. Using a manipulative experiment in the back reef of Moorea, French Polynesia, we tested if the macroalgaTurbinaria ornataprovided an associational refuge from fish corallivores for small colonies of massivePoritesspp., and how this differed with colony size (20–100 mm diameter). Tissue loss through corallivory increased with colony size but was ~ 72% less forPoritescolonies associated withT. ornataversus colonies separated from this macroalga, while dense macroalgae beds on contemporary reefs negatively impact the recruitment, growth and survival of corals, small colonies ofPoritesappear to benefit, through reduced corallivory, by associating with the macroalgaTurbinaria. This association may come at a cost (e.g., reduced growth) and should be the focus of future research. 

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4. Corallivory varies with water depth to influence the growth of Acropora hyacinthus , a reef‐forming coral

   https://doi.org/10.1002/ecs2.3623  

   Ladd, Mark C.; Winslow, Erin M.; Burkepile, Deron E.; Lenihan, Hunter S. (August 2021, Ecosphere)