We demonstrated that browser species specifically contribute to reduced macroalgae cover, and other studies have found that browser foraging behavior may result in higher rugosity reefs, as bites from browser species typically do not erode reef substrate. Little is known about the ecological factors contributing to “re-sheeting,” but it is hypothesized that grazing from herbivores provides top-down control of algal growth and promotes coral recovery. The principal threat to corals is the rise in sea temperature associated with global climate change. doi: 10.3354/meps12600, Adam, T. C., Kelley, M., Ruttenberg, B. I., and Burkepile, D. E. (2015b). Elkhorn Coral form shallow marine sediment s. It is a photosymbiotroph. Sci. (2007). (2006). Elkhorn is a city located in Wisconsin.With a 2020 population of 10,208, it is the 92nd largest city in Wisconsin and the 3059th largest city in the United States. Ecol. The branches can grow out to over 6.5 feet. 62, 75–84. Elkhorn Coral was once very abundant, but in recent decades it has remained at low levels of abundance, with no signs of recovery and in some areas, continued decline. Fossil data from multiple locations indicates that Atlantic elkhorn coral, Acropora palmata, formed shallow reefs throughout the Caribbean Sea since the Pleistocene. Oecologia 168, 1079–1090. doi: 10.1371/journal.pone.0096140, Rotjan, R. D., and Lewis, S. M. (2006). Go-Pro cameras (Hero 4) in underwater housings were used to record benthic images along each transect, remaining ~25 cm above the benthos. PLoS ONE 10:e0130312. Additionally, herbivorous fishes have larger foraging ranges (up to 0.5 hectares) so the grazing pressure from fish is more diffuse due to their roaming behavior (Carpenter, 1986; Sandin and McNamara, 2012; Adam et al., 2015a). Most Elkhorn Corals are Found on Spur and Groove Reefs. Elkhorn coral received its common name due to its resemblance to elk antlers. Endangered Species Act in May 2006. Over the past 30 years a strong population reduction has been registered due fundamentally to the white-band disease. Habitat complexity and consumer-mediated positive feedbacks on a Caribbean coral reef. Mar. Nature 429, 827–833. Mar. (2009). Mar. Transects were 20 m long, with all benthic information recorded within 1 m on each side and parrotfish observed within 2 m on either side. Additionally, we used a visual estimate for reef relief; however, studies quantifying rugosity and Diadema abundances would be more informative in quantifying the relationship not only between Diadema and reef complexity but also in developing predictions of accurate Diadema densities based on reef rugosity. PLoS ONE 12:e0174855. Towards automated annotation of benthic survey images: variability of human experts and operational modes of automation. Due to their tree-like growth form, elkhorn corals provide complex habitat for fish and other coral ree… World Wide Web Electron. Like its name suggests, staghorn coral is a species of coral that looks a bit like the antlers of a male deer. (B) An example of re-sheeting growth over a relict elkhorn colony. (6). Hagedorn et al. Potential sources of coral mortality include invasive microbes that become trapped in the surface mucus and thrive under conditions of increased coral stress. Diadema counts from paired day/night transects. Catastrophes, phase shifts and large-scale degradation of a Caribbean Coral Reef. 37, 297–317. 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. Restoration of critically endangered elkhorn coral (Acropora palmata) populations using larvae reared from wild-caught gametes . The spatial extent of grazing pressure can also influence effectiveness of top-down control of macroalgal growth. 162, 2029–2045. Macroalgae was observed on every transect, so the step two mixed-effects structure was used to estimate the effect of the predictor variables on percent cover of macroalgae. The IUCN Redlist for Threatened Species recommends research into the population abundance, ecology, habitat status, threats and coral restoration for elkhorn and staghorn corals. The greatest threat to staghorn coral is ocean warming, which causes the corals to release the algae that live in their tissue and provide them food, usually causing death. Average percent cover of elkhorn coral was determined from the point-count image analysis and ranged from 0 to 6.5% (Table 1). Conservation efforts resulted in a fish sanctuary being announced in 2015 (Yucatan Times, 2019) and a larger (1,653 hectare) Marine Refuge for Protected Species in 2016 (Official Gazette of the Federation, 2016), yet formal protection and management measures are still being developed. 56, 345–363. 335, 292–301. 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). doi: 10.1111/j.1461-0248.2005.00866.x, Cox, C., Valdivia, A., McField, M., Castillo, K., and Bruno, J. F. (2017). [10] At present, around one third of the world's reef-building corals are threatened with extinction. doi: 10.1016/j.csr.2015.04.015, Hughes, T. P. (1994). 563, 65–79. Adam, T. C., Burkepile, D. E., Ruttenberg, B. I., and Paddack, M. J. Colored dots indicate the depth zone of the survey (shallow: ≤11 m, deep: 12–17 m), which also correspond to structural complexity in this case (shallow = high relief; deep = low relief). Elkhorn coral can form dense groups called thickets in very shallow water. Mar. Several other threats have hurt the elkhorn population, including coral bleaching (loss of the … Most strikingly, we found that both herbivore populations contributed significantly to the presence of elkhorn coral. doi: 10.1007/s003380000125, Macintyre, I. G., and Toscano, M. A. The sea urchin Diadema antillarum–keystone herbivore or redundant species? When a storm or some other disturbance breaks apart a colony, each piece is able to reattach to the reef surface and begin growing again. While this study finds statistical correlations between Diadema density and parrotfish biomass with elkhorn live tissue cover, experimental manipulations of herbivore abundance and coral growth are needed to establish a causative effect. A total of 30–35 images were collected per transect and uploaded to CoralNet for analysis (Beijbom et al., 2015). If urchins are left out of management interventions, we may miss out on a critical component for coral reef recovery. Biol. The biomass (g/m2) and density (individuals per m2) of browser species was also calculated for each transect. Figure 2. Relationship between herbivore groups and elkhorn coral. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Regional Office. doi: 10.1007/s00227-013-2341-2, Mumby, P. J. Each black dot represents one transect survey (or spur). Coral Reefs 28, 555–568. Millions of male and female gametes are released into the water at the same time (usually synchronized with other adjacent colonies). This is one potential explanation for higher Diadema estimates in our models. The datasets generated for this study are available on request to the corresponding author. Of the 85 colonies surveyed, 43 were classified as re-sheeting and 37 of those colonies were in the largest size class (Figure 4); indicating that re-sheeting is contributing to a large portion of the total LAI and elkhorn cover on Akumal reefs. Elkhorn coral, or Acropora palmate, is a species of coral thought to be native to the Caribbean Sea. Demographic data for Elkhorn coral, Acropora palmata, and in situ water temperature data from seven upper Florida Keys (USA) reefs revealed three warm thermal stress events between 2010 and 2016. doi: 10.1016/0022-0981(80)90061-1, Sandin, S. A., and McNamara, D. E. (2012). McField, M., Kramer, P., Alvarez-Filip, L., Drysdale, I., Rueda Flores, M., Giro Peterson, A., et al. Mar. Predator and population density control of homing behavior in the Caribbean echinoid Diadema antillarum. Assessing the herbivore role of the sea-urchin Echinometra viridis: keys to determine the structure of communities in disturbed coral reefs. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. Zuur, A., Ieno, E. N., Walker, N. J., Saveliev, A. POPULATION ECOLOGY. Coral recovery, in general, is complex and any number of ecological or environmental mechanisms can contribute to the recovery of coral species, including recruitment and post-settlement survival (Ritson-Williams et al., 2009), capacity to cope with additional stressors (Mora et al., 2016), interactions with predators and competitors (Grober-Dunsmore et al., 2006), or variation in geographic area and management status (Graham et al., 2011). Our results suggest that historically important herbivore groups may be contributing to the recovery of elkhorn coral in Akumal by facilitating tissue re-sheeting. Science 345, 879–880. The Threatened Atlantic Elkhorn Coral, Acropora palmata: Population Dynamics and Their Policy Implications. Sci., 12 November 2019 Shelf Res. We observed higher Diadema density during our night surveys especially at shallower, high relief reef sites. Due to low sample size (n = 16), we could not include night time urchin density as a predictor in the models. We would like to thank Jenny Hughes for her help in the first few days of conducting fieldwork in Akumal, the staff at CEA and Akumal Dive Centre for providing logistical support in the field, and Dr. James Umbanhowar for statistical assistance. Smithson. Diadema and its relationship to coral spat mortality: grazing, competition, and biological disturbance. Dev. Coral Reefs 26, 71–78. The shallowest spur and groove set has a depth range generally ≤11 m, the middle set is ~12–16 m deep, and the deepest set is >16 m deep. Ecol. Figure 3. Survey Methods. The elkhorn coral Acropora palmata is coming back to the Belize Barrier Reef. Mote Marine Laboratory scientists are launching a new, underwater spawning nursery for elkhorn coral, with the goal of strategically breeding and restoring this rapidly declining, native species that is at risk of disappearing from Florida’s Coral Reef in our lifetime. Coral decline in the Caribbean is marked by the loss of habitat-forming corals, such as elkhorn coral (Acropora palmata). Additionally, we tested for sampling bias in counting Diadema urchins and found that a significant difference in urchins counts between paired day and night transects on shallow, high complexity reefs. The editor and reviewers' affiliations are the latest provided on their Loop research profiles and may not reflect their situation at the time of review. doi: 10.1007/BF00392768, Carpenter, R. C. (1986). April 2019; PeerJ 7; DOI: 10.7717/peerj.6751. Definition of size classes from Larson et al. Ecological limitations to the resilience of coral reefs. These sexually-bred corals therefore not only aid in the recovery of dwindling elkhorn coral populations by increasing the number of colonies, but also by increasing the genetic diversity of this critically endangered species, thus giving evolution the opportunity to play its part. (2018). Global Coral Reef Monitoring Network, IUCN, Gland. Both corals were listed as threatened on the U.S. 12, 45–54. Coral Reefs 27, 63–72. Table 3. In 2006, elkhorn coral was the first coral, along with its sister species, staghorn coral (Acropora cervicornis), to be included on the U.S. Front. J. Stat. 2015 Report Card for the Mesoamerican Reef. Table 2. Maximum depth, measured in meters, was used as the fixed effect because depth category of the spurs (deep or shallow) is confounding with site: meaning that sites were either deep or shallow, but not both. Figure 6. The species is also threatened by climate change impacts, including warming ocean temperatures, ocean acidification, and intensifying hurricanes. Because of the mixture of variables (depth, complexity) we cannot statistically attribute the differences in Diadema count due to any covariates other than time of day. doi: 10.1111/maec.12395, Wilson, S. K., Graham, N. A. J., and Polunin, N. V. C. (2007). (2015). How do coral reefs recover? doi: 10.1038/srep39670, Lacey, E. A., Fourqurean, J. W., and Collado-Vides, L. (2013). Specifically, we tested hypotheses that higher local density or biomass of herbivores corresponds to increased elkhorn presence, higher elkhorn live area index (LAI), and lower macroalgal percent cover. doi: 10.1155/2011/960207. The purpose of this study was to evaluate the status of elkhorn populations in Akumal, Mexico and determine if Diadema urchins or parrotfish populations are associated with higher elkhorn abundance and lower algal cover. [pic 5] “We just learned that elkhorn corals … Biol. Throughout its range, it has become more and more rare, and scientists now consider it to be critically endangered (very highly vulnerable to extinction). doi: 10.1111/j.0030-1299.2006.14247.x, Lessios, H. A., Robertson, D. R., and Cubit, J. D. (1984). The 12 m line indicates the separation between the “shallow” and “deep” sets of spur and groove reef areas. 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.). *Correspondence: Laura Mudge, lmudge@live.unc.edu, Front. Understanding the impacts of multiple grazer populations is important for management, and an ongoing debate of the relative importance of parrotfish and urchin populations in controlling macroalgal growth, specifically, has not been resolved (Adam et al., 2015a; Russ et al., 2015; Bruno et al., 2019). (7), Elkhorn Coral was once very abundant, but in recent decades it has remained at low levels of abundance, with no signs of recovery and in some areas, continued decline. 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). SAVING ELKHORN CORALS. Blue dots indicate average values at each site with bootstrapped standard errors. Spatial variation in sea urchins, fish predators, and bioerosion rates on coral reefs of Belize. 321, 123–132. Population assessment of staghorn (Acropora cervicornis) and elkhorn corals (A. palmata) in the upper Keys region of the Florida Keys National Marine Sanctuary Principal Investigator Steven L. Miller, Center for Marine Science, University of North Carolina at Wilmington (UNCW), We observed seven different species of parrotfishes, with species, average length (cm), and average weight (g) reported in Table 2. Many steps have been taken within the Dutch Caribbean to protect this and other valuable coral species. Mixed Effects Models and Extensions in Ecology with R. New York, NY: Springer. doi: 10.1111/j.1461-0248.2012.01861.x, Edmunds, P. J., and Carpenter, R. C. (2001). Elkhorn coral recovery has been isolated and patchy, but recently a “re-sheeting” phenomenon, in which elkhorn tissue grows over standing dead coral skeletons, was observed along the reefs in the Mexican Yucatán peninsula. These provide important habitat for other reef animals, especially fish. Elkhorn coral, along with staghorn coral and star corals built Caribbean coral reefs over the last 5,000 years. Mar. Elkhorn Coral colonies have suffered heavily from a variety of threats, notably white-band disease, bleaching and sedimentation. However, we may not have an accurate understanding of the contribution of Diadema to coral recovery on contemporary coral reefs. Our results also revealed increased coral presence and cover with increasing urchin populations and confirmed previous studies demonstrating that higher Diadema densities are associated with coral recovery (Edmunds and Carpenter, 2001; Carpenter and Edmunds, 2006; Myhre and Acevedo-Gutiérrez, 2007) and lower macroalgal cover (Carpenter and Edmunds, 2006; Myhre and Acevedo-Gutiérrez, 2007; Williams et al., 2016; Rodríguez-Barreras et al., 2018) in the Caribbean. Significant temporal variance in Diadema urchin counts. Parrotfish biomass was calculated from published length-weight ratios found on www.fishbase.org (see Table 2 for coefficient values used), using the equation: W = a × Lb (Froese and Pauly, 2000). However, we do know that grazing of benthic algae by herbivorous fishes and urchins is one mechanism of coral recovery which generally facilitates the survival and growth of juvenile or remnant corals (Edmunds and Carpenter, 2001; Hughes et al., 2007). Mora, C., Graham, N. A. J., and Nystrom, M. (2016). doi: 10.1890/05-1081. Elkhorn coral colonies can also reproduce through fragmentation (asexually). These sources of tissue damage should be closely monitored. Substratum-dependent predator-prey dynamics: patch reefs as refuges from gastropod predation. Rev. Prog. (2009). Abstract. Recovery Plan for Elkhorn (Acropora palmata) and Staghorn (A. cervicornis) Corals. Aquat. J. Exp. Mar. 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). Elkhorn coral, or Acropora palmate, is a species of coral thought to be native to the Caribbean Sea. J. Exp. Figure 8. Proc. ABSTRACT: Caribbean populations of the elkhorn coral Acropora palmata have declined due to environmental stress, bleaching, and disease. Elkhorn coral recovery has been isolated and patchy, but recently a “re-sheeting” phenomenon, in which elkhorn tissue grows over standing dead coral skeletons, was observed along the reefs in the Mexican Yucatán peninsula. National Marine Fisheries Service (2015). The abundance and density of herbivores also varies by site and depth (Figure 3). Biol. Prog. doi: 10.1016/0304-3770(76)90013-9, Precht, L. L., and Precht, W. F. (2015). doi: 10.2307/1942551, Carpenter, R. C., and Edmunds, P. J. A two-step hurdle modeling approach was used to evaluate the relationship between elkhorn coral and six predictor variables: total parrotfish biomass, biomass of parrotfish browser species, density of parrotfish browser species, Diadema density, maximum depth, and site. Elkhorn colonies and patches were grouped into three size classes (<60, 60–1,600, and >1,600 cm2) based on reproductive potential (Larson et al., 2014). Mar. Their numbers decreased rapidly beginning in the 1970s due … 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. Genetic analysis of the new coral found that its closest relative is Acropora abrotanoides. Akumal: Officially Decreed by Government as Fish Refuge. Sci. Monogr. Total parrotfish biomass and maximum depth were not significant terms and were dropped from the final model (Table 4). Modelling skewed data with many zeros: a simple approach combining ordinary and logistic regression. Mar. The high number of small bodied Redtail parrotfish species may be contributing to this trend (Table 2). 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". Softw. Genotypic variation in disease susceptibility among cultured stocks of elkhorn and staghorn corals. 6:683. doi: 10.3389/fmars.2019.00683. Thanks to a scientific petition the Center submitted, elkhorn and staghorn corals gained federal legal protection in 2006, becoming the first species listed under the Endangered Species Act because of vulnerability to global warming.