Herbivory and the resilience of Caribbean coral reefs: knowledge gaps and implications for management. Browsers typically feed on fleshy macroalgae, grazers on turf algae, and excavators on endolithic algae but take large bites that usually excavate the reef framework (Adam et al., 2015b, 2018). Survey Methods. Table 3. Rev. For patches or thickets of elkhorn coral in which it was not possible to delineate individual colonies, the total width and length of the thicket was measured, and estimated percent coverage of live tissue documented (similar to the estimation of percent mortality). Browser density, browser biomass, and maximum depth were not significant terms and dropped from the final model. Under stressful conditions, Elkhorn coral colonies and fragment growth slow down substantially. Early signs of recovery of Acropora palmata in St. John, US Virgin Islands. Acroporid coral populations have declined 80–90% throughout the Caribbean and western Atlantic since the late 1980s (Bruckner 2002), and both A. cervicornis (staghorn coral) and A. palmata (elkhorn coral) were listed as threatened species under the U.S. Towards automated annotation of benthic survey images: variability of human experts and operational modes of automation. At present, around one third of the world's reef-building corals are threatened with extinction. This finding is of a population of elkhorn coral in the Pacific is of particular scientific interest because it represents one morphological extreme in Acropora, the dominant genus of reef-building corals, the researchers say. Kuempel, C. D., and Altieri, A. H. (2017). Centro Ecológico Akumal. doi: 10.7287/peerj.preprints.1565v2, Renfro, B., and Chadwick, N. E. (2017). Once the most abundant and important reef-building corals in Florida and the Caribbean, elkhorn corals have declined by more than 90 percent in many areas, mainly as a result of disease and “bleaching. Coral reef recovery dynamics in a changing world. Mar. Official Gazette of the Federation (2016). doi: 10.1890/05-1081. doi: 10.3354/meps329205. This difference is more pronounced in the shallower, higher relief reefs (df = 9, t = −4.6, p = 0.001). Modelling the abundance of rare species: statistical models for counts with extra zeros. Top-down control of macroalgal growth is one ecological factor imperative for coral recovery, as this process provides physical space on the benthos for corals to settle or grow (Knowlton, 1992; Edmunds and Carpenter, 2001). Elkhorn coral is a large, branching coral with thick and sturdy antler-like branches. The elkhorn coral’s complex large and thick green colored branches can reach a length of 6.5 feet (two meters). doi: 10.1126/science.226.4672.335, Levitan, D. R., and Genovese, S. J. doi: 10.1007/s00338-010-0717-z, Grober-Dunsmore, R., Bonito, V., and Frazer, T. K. (2006). 7, 11246–11256. National Marine Fisheries Service (2015). Ecol. (A) Typical branching colony growth form. Local management interventions may be limited in the scope of problems that can be addressed; however, without mitigation of underlying causes of coral mortality such as ocean warming and coastal development, we should not expect herbivore protection or enhancement alone to increase coral resilience (Edmunds and Elahi, 2007; Adam et al., 2015a; Arias-González et al., 2017; Cox et al., 2017; Bruno et al., 2019). The main island of Puerto Rico has been identified as within the genetic population of the eastern Caribbean while Mona Island has been proposed as a mixing zone for the eastern and western populations for the species (Baums et al. Nature 429, 827–833. Coral Reefs 30, 283–294. Total parrotfish biomass and maximum depth were not significant terms and were dropped from the final model (Table 4). Elkhorn coral in the US Caribbean. Yucatan Times. Parrotfish biomass ranged from ~2–43 g/m2. Oecologia 168, 1079–1090. The habitat and spatial heterogeneity of both coral and Diadema populations demonstrates the need for location-specific information for evaluating associations between herbivory and coral recovery. Substratum-dependent predator-prey dynamics: patch reefs as refuges from gastropod predation. 77, 3–18. Managers and researchers could work together toward finding and cultivating ideal site-specific Diadema population sizes: large enough to exhibit top-down control of macroalgal growth and promote coral recovery, but not so dense that urchin grazing harming coral recruitment by consuming coral spat or further eroding the reef substrate (Sammarco, 1980; Korzen et al., 2011; Sandin and McNamara, 2012). Complementary linear mixed-effects models indicate that Diadema density was a better predictor than parrotfish biomass of total elkhorn tissue live area index, although the fixed effects only contributed to a small portion of the variance. Assessment of Acropora palmata in the mesoamerican reef system. 120, 202–213. Create your own unique website with customizable templates. Available online at: http://www.dof.gob.mx/nota_detalle.php?codigo=5428829&fecha=07/03/2016 (accessed May 13, 2019), Ogden, J. C. (1976). Often referred to as “rainforests of the sea,” coral reefs are perhaps the greatest, most vibrant expressions of ocean life. Upper growth is determined by wave forces, while the lower growth is determined by the availability of light and the quantity of suspended sediments (National Oceanic & Atmospheric Administration n.d.). Elkhorn Coral form shallow marine sediment s. It is a photosymbiotroph. We observed higher Diadema density during our night surveys especially at shallower, high relief reef sites. 2011, 1–8. PLoS ONE 12:e0184175. Comparative analysis of foraging behavior and bite mechanics reveals complex functional diversity among Caribbean parrotfishes. Official Gazette of the Federation. Within four years after the white pox was found, the population of elkhorn coral in that reef had decreased by 82 percent. Diadema density (estimate = −5.84; p = 0.001) and browser species biomass (estimate = −3.95, p = 0.032) had statistically significant negative correlations with macroalgal cover. Mar. Coral Reefs 19, 392–399. The 12 m line indicates the separation between the “shallow” and “deep” sets of spur and groove reef areas. Acad. Roy, R. E. (2004). 8:14160. doi: 10.1038/ncomms14160, Darling, E. S., Alvarez-Filip, L., Oliver, T. A., Mcclanahan, T. R., and Cote, I. M. (2012). Like its name suggests, staghorn coral is a species of coral that looks a bit like the antlers of a male deer. Populations of the shallow-water Caribbean elkhorn coral, Acropora palmata , are being decimated by white pox disease, with losses of living cover in the Florida Keys typically in excess of 70%. Resource partitioning along multiple niche axes drives functional diversity in parrotfishes on Caribbean coral reefs. Mar. Diadema can be hard to detect on structurally complex reefs due to their nocturnal feeding behavior, as they are known to seek refuge from predators during the day (Ogden, 1976; Levitan and Genovese, 1989). Captive breeding techniques may also one day be critical to the species’ survival, should staghorn coral populations continue trending downward. Our results support recommendations to enhance herbivore populations as one mechanism to promote coral recovery and control macroalgal growth on degraded coral reefs (Adam et al., 2015a; Williams et al., 2016). Res. Mora, C., Graham, N. A. J., and Nystrom, M. (2016). This is one potential explanation for higher Diadema estimates in our models. Of those in the larger size class, we documented 15 colonies of a typical branching form, 25 observations of continuous re-sheeting over relict elkhorn skeleton, 12 observations of patchy re-sheeting colonies, and 8 thickets which contained a series of branching colonies (see Figure 1 for examples of form classification). doi: 10.1017/S1755267209990662, Carpenter, R. C. (1984). Scientists have been calling for management initiatives that will aid in the recovery of herbivore populations as one way to boost coral recovery. Lett. This means that sunlight is essential, and they are particularly sensitive to any human activities that increase water turbidity, reducing light availability. Staghorn coral populations on one reef exhibit limited ability to seed another population separated by large distances. Prog. Elkhorn coral (Acropora palmata) was once dominant on Florida and Caribbean reefs, but its populations have declined 97% in the past four decades, ... and represent the next generation of genetically diverse individuals to “recruit” back into a self-sustaining population. Diadema urchins are known bioeroders, meaning they can remove the hard carbonate substrate of the reef; therefore, benthic habitats with poor or no coral recruitment can also be flattened by grazing of extremely high-density urchin populations (Bak, 1994). Photos: elkhorn coral spawning and collection of their gametes. Map of the study region. Biol. Due to their tree-like growth form, elkhorn corals provide complex habitat for fish and other coral ree… doi: 10.1007/s00338-007-0291-1. No use, distribution or reproduction is permitted which does not comply with these terms. The biomass (g/m2) and density (individuals per m2) of browser species was also calculated for each transect. Ecol. Sci. (6). Am. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Regional Office. Mar. Staghorn coral can form dense groups called thickets in very shallow water. doi: 10.5343/bms.2012.1015, Larson, E. A., Gilliam, D. S., Padierna, M. L., and Walker, B. K. (2014). Mar. Relationship between herbivores and macroalgae cover. Pollution, climate change and other stressors cause the algae to be expelled from the coral’s tissues, which makes them lose their major source of food and their colour – a process called coral bleaching. Elkhorn coral is considered to be one of the most important reef-building corals in the Caribbean and it was the first coral species in the world to receive ... the Critically Endangered Elkhorn coral (Acropora palmata), a once abundant coral species which has seen a dramatic population reduction exceeding 80% over the past 30 years". We found that even at low abundances, these herbivore groups are associated with less macroalgal cover, although experimental grazing studies are needed to quantify the magnitude of this effect. Strong associations between elkhorn abundance and Diadema populations in Akumal suggest that Diadema reintroduction may be an appropriate tool for local managers when developing holistic coral recovery or restoration plans (Adam et al., 2015a; Precht and Precht, 2015). 2005). Parrotfish species were assigned functional groups based on feeding strategy and the proportion of biomass and total individuals observed was calculated for each group (browser, scraper, and excavator). Elkhorn coral is much less abundant than staghorn coral and NSU scientists estimate that the remaining Keys’ population is . doi: 10.1073/pnas.071524598, Edmunds, P. J., and Elahi, R. (2007). doi: 10.1007/s00227-006-0538-3, Yucatan Times (2019). Image found on William B Tomanek's Photography website. Both corals were listed as threatened on the U.S. Elkhorn (Acropora palmata) and staghorn (A. cervicornis) corals were listed as threatened under the U.S. The Elkhorn coral (Acropora palmata) is a Critically Endangered stony coral species distributed in the Caribbean, Gulf of Mexico, Florida and the Bahamas. doi: 10.1126/science.265.5178.1547, Hughes, T. P., Rodrigues, M. J., Bellwood, D. R., Ceccarelli, D., Hoegh-Guldberg, O., McCook, L., et al. doi: 10.1111/j.0030-1299.2006.14247.x, Lessios, H. A., Robertson, D. R., and Cubit, J. D. (1984). Mar. Estimated regression parameters, standard error, z-value or t-value, and p-values from the final linear mixed-effects models. (A) Location of Akumal, Mexico on the Yucatán Peninsula; (B) Survey site locations on Akumal coral reefs, made with Google Earth. Over the past 30 years a strong population reduction has been registered due fundamentally to the white-band disease. Coral Reefs 28, 761–773. Science 226, 335–337. Yet due to global warming, already-delicate coral reefs throughout the Caribbean and along the coast of Florida are vanishing at unprecedented rates. Jackson, J., Donovan, M., Kramer, K., and Lam, W. (2014). Patterns of coral ecosystem degradation in Akumal mirror past Caribbean region-wide decline of herbivores and corals from overfishing, hurricanes, and disease (Roy, 2004). Staghorn and Elkhorn coral are harvested for building materials, souvenirs, jewelery, and for aquariums. doi: 10.1016/j.cub.2006.12.049. Most Elkhorn Corals are Found on Spur and Groove Reefs. Also, sedimentation threatens the elkhorn coral’s marine habitat, as the increased sediment prevents light from reaching the lower portion of the coral preventing lower growth. Even though total parrotfish biomass was not correlated to lower macroalgal cover, fish grazing activity from non-browser species may have other positive benefits such as contributing to increased coral calcification (Suchley and Alvarez-Filip, 2017) or overall reef accretion (Cramer et al., 2017). However, the bay area in Akumal is a distinctly different reef structure than the spur-and-groove forereef. Prog. Fish. Biodivers. Rep. 7, 1–10. 162, 2225–2233. Ecol. Water quality assessment in the Mexican Caribbean: impacts on the coastal ecosystem. Sci. The branches can grow out to over 6.5 feet. Diadema density recorded in the day-time ranged from 0 to 1.2 individuals per m2, with an average of 0.18 individuals/m2 across all sites. Coral Reefs 13, 99–103. Go-Pro cameras (Hero 4) in underwater housings were used to record benthic images along each transect, remaining ~25 cm above the benthos. Figure 4. Trop. Elkhorn coral is one of the most important corals in the Caribbean. doi: 10.1093/icb/32.6.674, Korzen, L., Israel, A., and Abelson, A. For each elkhorn colony or patch observed, we measured the colony size (length, width, and height in cm); estimated percent mortality; and documented observations of lesions from disease or predation, bleaching, fish bites, worms, and overgrowth.

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