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. Mar. Apparent stability of a low-density Diadema antillarum regime for Puerto Rican coral reefs. Silver Spring, MD. Lett. 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. Due to low sample size (n = 16), we could not include night time urchin density as a predictor in the models. Even though Diadema density was a significant predictor of elkhorn LAI, fixed effects in the final model did not account for a substantial amount of the variance (Table 3; marginal R2 = 0.158). (2007). Total parrotfish density was not used as a predictor variable due to high collinearity with biomass and fish biomass is the more ecologically relevant variable for this study. 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. By Tali Vardi. Sci. 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). doi: 10.1007/s00442-011-2156-0, Sangil, C., and Guzman, H. M. (2016). Akaike information criterion (AIC) values were used to evaluate competing models. 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. ScienceDaily . Bio. doi: 10.1007/s00227-015-2748-z, Graham, N. A. J., Nash, K. L., and Kool, J. T. (2011). 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. We also found that higher Diadema density and parrotfish browser species biomass was correlated with lower macroalgal cover, even at low abundances. We recorded parrotfish species, number of individuals of each species, initial or terminal phase, and estimated size (cm). Cryopreservation-Assisted Gene Flow in Elkhorn Coral 5 and helps each population achieve high fertilization rates, but this compression in time dramatically limits the ability of conservationists to work with, transport, and cross-fertilize germplasm from these animals. No use, distribution or reproduction is permitted which does not comply with these terms. Spatial dynamics of benthic competition on coral reefs. The coral is so named because it looks like the antlers found on many species of elk. Coral decline in the Caribbean is marked by the loss of habitat-forming corals, such as elkhorn coral (Acropora palmata). We measured 85 elkhorn colonies or patches and found that a majority (n = 60) had a LAI >1,600 cm2 (Figure 4). Figure 8. Mar. We hypothesized that the “re-sheeting” phenomenon of elkhorn coral observed in Mexico was related to this top-down control of algal growth, since coral tissue is growing over bare surfaces of relic corals, not up into newly formed 3D structures. (2018). Sci. The branches can grow out to over 6.5 feet. Ecol. Population metrics and behaviors of excavator species, however, should be monitored to prevent excessive substrate erosion or corallivory, which could lead to coral mortality of other reef-building corals (Rotjan and Lewis, 2006; Cardoso et al., 2009; Burkepile, 2012; Bruno et al., 2019). 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). 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. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Regional Office. doi: 10.1007/s00338-009-0506-8, Myhre, S., and Acevedo-Gutiérrez, A. Ann. Res. 45, 245–272. 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 contributed equally to this work. doi: 10.1073/pnas.071524598, Edmunds, P. J., and Elahi, R. (2007). More robust information on herbivore population dynamics may also benefit in-water conservation projects, such as coral nurseries, as knowledge of local herbivore densities can provide guidance on geographic areas where outplanted coral fragments might have a higher competitive advantage due to grazing of macroalgae (Sandin and McNamara, 2012; Adam et al., 2015a; Precht and Precht, 2015). doi: 10.1093/icb/32.6.674, Korzen, L., Israel, A., and Abelson, A. Abstract. Transects were geolocated using surface GPS waypoints and starting points marked with flagging tape so we could return to the exact same spurs at night to recount Diadema urchins, for a total of 16 paired day-night Diadema surveys. Biol. 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). How do coral reefs recover? Figure 6. Mar. 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. Linear mixed-effects models revealed that Diadema urchins have a statistically significant positive correlation on the amount of live elkhorn tissue (estimate = 1.66, p = 0.032) and total parrotfish biomass has a small, nearly statistically significant correlation (estimate = 0.04, p = 0.094; Table 3, Figures 6C,D). Staghorn coral populations on one reef exhibit limited ability to seed another population separated by large distances. [pic 5] “We just learned that elkhorn corals … Elkhorn is currently growing at a rate of 1.04% annually and its population has increased by 1.23% since the most recent census, which recorded a population of 10,084 in 2010. Fitting linear mixed-effects models using lme4. (A) Location of Akumal, Mexico on the Yucatán Peninsula; (B) Survey site locations on Akumal coral reefs, made with Google Earth. 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). Within four years after the white pox was found, the population of elkhorn coral in that reef had decreased by 82 percent. Competition between macroalgae and corals: effects of herbivore exclusion and increased algal biomass on coral survivorship and growth. Parrotfish biomass ranged from ~2–43 g/m2. Significant temporal variance in Diadema urchin counts. In Akumal, high damselfish density and turf algae cover has been observed the past few years (Figueroa-Zavala and Munoz Arroyo, 2018). Knowlton, N. (1992). For example, the Fortuna Reefer Vessel grounding site showed no measurable … Ser. 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). 2018 Report Card for the Mesoamerican Reef. Restoration of critically endangered elkhorn coral (Acropora palmata) populations using larvae reared from wild-caught gametes . Adam, T. C., Burkepile, D. E., Ruttenberg, B. I., and Paddack, M. J. As a result of disease, pollution, coral bleaching, and storm damage, populations of elkhorn corals have crashed. Many steps have been taken within the Dutch Caribbean to protect this and other valuable coral species. Over the past 30 years a strong population reduction has been registered due fundamentally to the white-band disease. 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. (2015). 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). The majority of elkhorn colonies observed were large in size (>1,600 cm2) and exhibited the re-sheeting growth form. 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. The calculation used for live area index (LAI) is: (W * L * % Live tissue)/100 in units cm2 (Larson et al., 2014). Sci. Acad. Browser density, browser biomass, and maximum depth were not significant terms and dropped from the final model. 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. Environ. The 12 m line indicates the separation between the “shallow” and “deep” sets of spur and groove reef areas. We conducted this study on the coral reefs of Akumal, Mexico (Figure 2), where elkhorn re-sheeting was observed in recent years. Effects of herbivores, nutrient enrichment, and their interactions on macroalgal proliferation and coral growth. Trop. (2009). 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. Model selection revealed that browser density, browser biomass, and maximum depth were not significant predictors and were not included in the final model (Table 4). Sci. Atlantic Acropora species are believed to be most greatly threatened by disease, temperature-induced bleaching, and physical damage from hurricanes. 3, 1–43. Trop. Water quality assessment in the Mexican Caribbean: impacts on the coastal ecosystem. Mar. 161, 359–365. Context-dependent corallivory by parrotfishes in a Caribbean reef ecosystem. ” Threats related to Global Warming. Millions of male and female gametes are released into the water at the same time (usually synchronized with other adjacent colonies). Ecol. doi: 10.3354/meps11984, Cramer, K. L., O'Dea, A., Clark, T. R., Zhao, J., and Norris, R. D. (2017). (2006). Elkhorn coral survey and demographic information. doi: 10.1007/s00442-015-3406-3, PubMed Abstract | CrossRef Full Text | Google Scholar, Arias-González, J. E., Fung, T., Seymour, R. M., Garza-Pérez, J. R., Acosta-González, G., Bozec, Y. M., et al. Figueroa-Zavala, B., and Munoz Arroyo, N.-H. (2018). Patterns of coral ecosystem degradation in Akumal mirror past Caribbean region-wide decline of herbivores and corals from overfishing, hurricanes, and disease (Roy, 2004). Dev. doi: 10.1023/A:1013103928980, Bak, R. P. M. (1994). Yet, little is known about the abundance of elkhorn populations in Akumal and what factors may be contributing to the re-sheeting phenomenon observed on these spur-and-groove reefs. Sexual reproduction occurs only once per year in August or September. Spread of diadema mass mortality through the Caribbean. Rep. 7, 1–10. Am. This in turn, when extreme, can reduce coral settlement and recruitment and slow population recovery (Knowlton, 1992; Hughes, 1994; Edmunds and Carpenter, 2001; Mumby, 2009). Coral Reefs 26:757. doi: 10.1007/s00338-007-0268-0, McClanahan, T. R., and Muthiga, N. A. 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). Ser. Variation in elkhorn and herbivore populations across survey sites in Akumal, Mexico. PLoS ONE 12:e0174855. Ecol. Diadema were present on deeper, lower relief sites, yet there was no difference between Diadema counts during day and night surveys (Figure 8). To address the issue of inaccurate population estimates of Diadema urchins, day-time survey protocols should be supplemented with evening or night surveying, especially on high relief reefs where more urchins may be completely hidden during daylight hours. During asexual reproduction, or asexual fragmentation, branches of coral break off and attach to the ocean floor. Bull. Diadema were not observed in belt transects in 3 out of our 12 sites (BPS, LR, HMBP). Roy, R. E. (2004). Monogr. Rev. doi: 10.1017/S1755267209990662, Carpenter, R. C. (1984). 2, 103–116. doi: 10.3354/meps321123, Hernández-Terrones, L. M., Null, K. A., Ortega-Camacho, D., and Paytan, A. We found that, overall, the presence of elkhorn coral and amount of live tissue increased with increasing herbivore density or biomass. The sea urchin Diadema antillarum–keystone herbivore or redundant species? The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Aquat. This study did not test for bottom-up forcing from nutrients; although previous studies demonstrated a correlation between tourism, a proxy for nutrient influx, and declining reef condition in Akumal Bay (Gil et al., 2015; Renfro and Chadwick, 2017) and documented sources of anthropogenic nutrient input to Akumal waters (Hernández-Terrones et al., 2015). 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. Ecology of Echinometra. 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. 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. 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. doi: 10.1371/journal.pone.0130312, Bellwood, D. R., Hughes, T. P., Folke, C., and Nystro, M. (2004). Ecol. Ecological assessments of the coral reef communities in the Eastern Caribbean and the effects of herbivory in influencing coral juvenile density and algal cover. 77, 3–18. Credit: NOAA ... with only 20% of their populations remaining today. Mar. J. Exp. All predictor variables were centered and scaled prior to modeling. 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. This difference is more pronounced in the shallower, higher relief reefs (df = 9, t = −4.6, p = 0.001). Elkhorn coral actively fighting off diseases on reef: Findings showed coral has core immune response regardless of disease type. 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. (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. Vermeij, Mike Brittsan, Mitch Carl, Mark Schick, Skylar Snowden, Adriaan Schrier and Dirk Petersen.