Jackson, J., Donovan, M., Kramer, K., and Lam, W. (2014). It has asexual reproduction, alternation of generations, and sexual reproduction. Yucatan Times. (2009). It is listed as critically endangered by IUCN and in CITES Appendix II. Elkhorn coral (Acropora palmata) was once dominant on Florida and Caribbean reefs, but its populations have declined 97% in the past four decades, particularly due to white band disease. doi: 10.1038/nature02691, Bonito, V., and Grober-Dunsmore, R. (2006). Diadema urchins were more common in shallow sites (max density: 1.2/m2, mean density: 0.35/m2) and present but rare at sites deeper than 12 m (Figure 3, mean density: 0.017/m2). Their colonies are fast growing and branches increase in length by 2-4 inches per year, with colonies reaching their maximum size in approximately 10-12 years. Herbivore Populations and the Presence of Elkhorn Coral. Biol. Recently, a “re-sheeting” phenomenon, in which elkhorn tissue grows over relict coral skeletons (Bonito and Grober-Dunsmore, 2006), was observed along the reefs in the Mexican Yucatán peninsula (Bruno, 2014; Rodríguez-Martínez et al., 2014). doi: 10.1111/maec.12395, Wilson, S. K., Graham, N. A. J., and Polunin, N. V. C. (2007). Diadema and its relationship to coral spat mortality: grazing, competition, and biological disturbance. Fletcher, D., MacKenzie, D., and Villouta, E. (2005). Diadema populations remain low throughout the Caribbean, but locally high populations may contribute more grazing pressure to the top-down control of macroalgae. Mar. Ser. Science 265, 1547–1551. doi: 10.1007/s00338-011-0824-5, Cardoso, S. C., Soares, M. C., Oxenford, H. A., and Côté, I. M. (2009). Fish. Resheeting of relict Acropora palmata framework may promote fast growth but does it compromise the structural integrity of the colony? 2005). Lastly, even when elkhorn recovery is documented, tissue damage from predatory snails (e.g., Coralliophila abbreviata) and damselfish grazing (from the cultivation of turf algal “gardens”) may stifle the full potential for regrowth (Grober-Dunsmore et al., 2006). Ser. Relationship between herbivore groups and elkhorn coral. doi: 10.1038/srep39670, Lacey, E. A., Fourqurean, J. W., and Collado-Vides, L. (2013). For all plots, black dots represent raw data points, blue dots and lines represent unscaled model estimates and 95% confidence intervals from the final model. Mar. 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). Potential sources of coral mortality include invasive microbes that become trapped in the surface mucus and thrive under conditions of increased coral stress. Curr. 108, 101–108. Spatial dynamics of benthic competition on coral reefs. Within four years after the white pox was found, the population of elkhorn coral in that reef had decreased by 82 percent. (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. PLoS ONE 9:e96140. Sci. Modell. Mar. (A) Negative association between Diadema density and macroalgae; (B) Negative association between parrotfish browser species biomass and macroalgae; (C) Positive association between parrotfish browser density and macroalgae. Figure 1. 520, 1–20. 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. Parrotfish biomass ranged from ~2–43 g/m2. Nat. A robust parrotfish guild can provide complementary functions to promote reef recovery, including removal of different species of algae (macro vs. turf) and removal of dead coral which can provide space for new coral settlement or growth (Cardoso et al., 2009). Significant temporal variance in Diadema urchin counts. 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. Our results suggest that historically important herbivore groups may be contributing to the recovery of elkhorn coral in Akumal by facilitating tissue re-sheeting. Species were classified as browser, scraper, or excavator based on previous analysis from Adam et al. The reduction of herbivory has led to an increased cover and biomass of macroalgae (Hughes, 1994; Aronson and Precht, 2000). Grazing effects of fish versus sea Urchins on turf algae and coral recruits: possible implications for coral reef resilience and restoration. 161, 359–365. The recovery of elkhorn coral is a conservation priority because its unique branching structure provides habitat for countless other reef organisms, its critical role in reef accretion due to fast growth, and its role in buffering coastlines from wave action (Aronson and Precht, 2001; Bellwood et al., 2004; National Marine Fisheries Service, 2015). Coral Reefs 19, 392–399. doi: 10.1007/s003380000125, Macintyre, I. G., and Toscano, M. A. To achieve this objective, we surveyed 12 spur and groove reef sites in Akumal, where re-sheeting was recently observed, and measured elkhorn coral and herbivore population metrics. vessel groundings, anchors, divers, snorkelers), coastal development, competition and predation are deemed to be moderate. Ecol. Assessment of Acropora palmata in the mesoamerican reef system. Figure 8. doi: 10.1007/s00338-016-1479-z, Morrison, D. (1988). For all plots, black dots represent raw data points, blue dots, and lines represent unscaled model estimates and 95% confidence intervals from the final model. The principal threat to corals is the rise in sea temperature associated with global climate change. A., and Smith, G. M. (2009). This species is particularly susceptible to bleaching. doi: 10.1146/annurev-marine-010318-095300, Burkepile, D. E. (2012). Roy, R. E. (2004). Population declines of staghorn coral (Acropora cervicornis) and elkhorn coral (A. palmata) are often-cited examples of Caribbean reef change since the 1970s, due, in part, to disease and localized effects from storms and predation. Prepr. Oecologia 168, 1079–1090. Available online at: http://www.healthyreefs.org (accessed January 4, 2016). (2018). The branches can grow out to over 6.5 feet. Die verzweigte Struktur schafft Lebensraum und Schutz für viele andere Riffarten. Bio. 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. This correlation may also be due to positive feedbacks associated with structural complexity and Diadema populations (Lee, 2006). While gaps in our knowledge persist regarding the ecological factors contributing to coral recovery, results here suggest that both herbivore groups contribute to elkhorn abundance. doi: 10.1016/j.cub.2006.12.049. Ser. 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. Browser species density had a significant positive correlation to macroalgal cover (estimate = 4.0, p = 0.007; Table 3, Figure 7). ” Threats related to Global Warming. doi: 10.1016/j.csr.2015.04.015, Hughes, T. P. (1994). 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.). doi: 10.1007/s10651-005-6817-1. Elkhorn Coral colonies have suffered heavily from a variety of threats, notably white-band disease, bleaching and sedimentation. (2011). 88, 297–308. (2015). doi: 10.1023/A:1013103928980, Bak, R. P. M. (1994). doi: 10.1007/s00338-009-0506-8, Myhre, S., and Acevedo-Gutiérrez, A. Official Gazette of the Federation (2016). We also found that higher Diadema density and parrotfish browser species biomass was correlated with lower macroalgal cover, even at low abundances. J. Mar. Akumal: Officially Decreed by Government as Fish Refuge. 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. This difference is more pronounced in the shallower, higher relief reefs (df = 9, t = −4.6, p = 0.001). 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). (B) An example of re-sheeting growth over a relict elkhorn colony. 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). Diadema were present on deeper, lower relief sites, yet there was no difference between Diadema counts during day and night surveys (Figure 8). Official Gazette of the Federation. population structure and signs of selection in the threatened Caribbean elkhorn coral, Acroporapalmata Meghann K. Devlin-Durante *and Iliana B. Baums Department of Biology, Pennsylvania State University, University Park, PA, United States of America * These authors … POPULATION ECOLOGY. Each colony contains both male and female structures, and is simultaneously hermaphroditic. CTB refers to a combined category of coralline algae, turf algae, and bare substrate, and is used when the identification at the specific point cannot be resolved in the images. The sea urchin Diadema antillarum–keystone herbivore or redundant species? The threat from collection or harvest was deemed abated by effective national and international regulations. J. Exp. (2007). The number one threat for coral reefs globally is climate change. Figure 2. doi: 10.1007/BF00300768, Bates, D., Maechler, M., Bolker, B., and Walker, S. (2015). Herbivory facilitates growth of a key reef-building Caribbean coral. Apparent stability of a low-density Diadema antillarum regime for Puerto Rican coral reefs. Table 1. with 82% of the population dying off four years after being discovered (National Park Service, n.d.). Elkhorn coral is a large, branching coral with thick and sturdy antler-like branches. Browser species, which typically feed on fleshy macroalgae, comprised the largest proportion of biomass and individuals observed (42 and 51%, respectively), although excavator species made up a comparable 39% of the total biomass (Figure 5). (2016). Elkhorn coral primarily reproduces asexually; however, they are capable of producing sexually. Biol. Confronting the coral reef crisis. Centro Ecológico Akumal. Elkhorn coral can span a diameter of 4 m (12 feet) wide and 2 m(6 feet) tall. doi: 10.1007/s00338-006-0159-9, Bruno, J. F. (2014). Mora, C., Graham, N. A. J., and Nystrom, M. (2016). FishBase. 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). Under stressful conditions, Elkhorn coral colonies and fragment growth slow down substantially. Coral Reefs 30, 283–294. Ecological limitations to the resilience of coral reefs. Context-dependent corallivory by parrotfishes in a Caribbean reef ecosystem. (2014) and classification of a colony or patch determined from LAI measurement (cm2). *Correspondence: Laura Mudge, lmudge@live.unc.edu, Front. Water quality assessment in the Mexican Caribbean: impacts on the coastal ecosystem. We conducted 55 transect surveys from May to August 2016 at 12 reef sites, covering approximately 2,200 m2 of benthic habitat over a 10 km stretch of coastline. doi: 10.1016/0022-0981(89)90198-6, Lirman, D. (2001). Blue dots indicate average values at each site with bootstrapped standard errors. (2017). White-band disease and the changing face of Caribbean coral reefs. Efforts to protect and potentially enhance fish populations are already underway through designation of a fish sanctuary and marine reserve in Akumal (Official Gazette of the Federation, 2016; Yucatan Times, 2019). Sci. Mar. Figueroa-Zavala, B., and Munoz Arroyo, N.-H. (2018). The Elkhorn coral (Acropora palmata) is a Critically Endangered stony coral species distributed in the Caribbean, Gulf of Mexico, Florida and the Bahamas. 6:683. doi: 10.3389/fmars.2019.00683. Several other threats have hurt the elkhorn population, including coral bleaching (loss of the … Natl. These provide important habitat for other reef animals, especially fish. 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. 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). Captive breeding techniques may also one day be critical to the species’ survival, should staghorn coral populations continue trending downward. Authors: Margaret Miller. Appraisal of visual assessments of habitat complexity and benthic composition on coral reefs. (2006). Relatives of the sea anemone and every bit as splashy, corals display hues ranging from brilliant orange and deep salmon to pale pink and subtle violet. We used paired t-tests to evaluate the difference in Diadema density between day and night surveys. 563, 65–79. 2011, 1–8. Rec. We found that both herbivore groups are associated with increasing elkhorn coral presence and cover, and lower macroalgal cover. 2018 Report Card for the Mesoamerican Reef. Publ. 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. 7, 11246–11256.
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