Abstract Two species of Echinometra are found on tropical western Atlantic reefs. E. viridis and E. lucunter. Both are grazers and bioeroders, and on some disturbed reefs E. viridis has become the dominant herbivore, particularly since the disease-caused decline of the much larger echinoid Diadema antillarum. Thus, it is critical to understand factors affecting herbivory by Echinometra, including foraging behaviors and distances, diel and lunar cycles of foraging, and densities of Echinometra, particularly E. viridis, across habitats and locations. Twenty-four hour tracking studies undertaken in the San Blas Islands of Panama, conducted at different times in the lunar cycle, revealed that on new moons both species of Echinometra primarily moved and fed at night, but the pattern reversed on full moons. These data suggest that vulnerability to predators and/or aggression by damselfishes during the night on full moons may be a significant selective force affecting diel foraging behavior. Daily distances moved (minimum estimate) averaged 19 cm for E. viridis and 11 cm for E. lucunter. The average foraging range for E. viridis was estimated to be 0.3–5% the size of that of D. antillarum, while per capita daily algal consumption by E. viridis is 20% that of D. antillarum.These results suggest more intense, localized grazing by E. viridis compared to D. antillarum. A review of published densities of E. viridis show that 50% of studied sites (location/habitat combination) have densities less than 5 m−2, a level unlikely to produce a strong herbivory effect. Densities greater than 15 m−2 were found at 25% of sites, including the San Blas Islands, Panama patch reefs in this study, which averaged 26 m−2. Where high densities are combined with low predator numbers due to fishing, E. viridis can have strong direct effects on algal assemblages, with potential indirect effects on corals and other benthic invertebrates. However, available published data indicate E. viridis has strong regional variation in abundance, as yet unexplained, that limits its potential Caribbean-wide role as a reef herbivore. Morphological traits of E. viridis that are likely related to vulnerability to predation varied across habitats. A newly-described melanic color morph comprised 4–16% of the population, with significant variation in frequency across habitat types. Body sizes (test diameter) also varied among habitats, with larger individuals much more common in habitats with fewer shelter sites. Similarly, in habitats offering less protection from predators, spine lengths were longer relative to test diameter. Morphological traits that reduce predator detection or vulnerability to predation, as well as the refuges afforded by habitat, will ultimately affect both the number of E. viridis on a particular reef and their ability to forage in the presence of predators.

中文翻译：

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加勒比珊瑚礁上的 Echinometra 海胆：日月和月球的运动和进食周期、密度和形态

摘要 在热带西大西洋珊瑚礁上发现了两种 Echinometra。E. viridis 和 E. lucunter。两者都是食草动物和生物侵蚀者，并且在一些受干扰的珊瑚礁上，绿色 E. viridis 已成为主要的食草动物，特别是因为更大的海胆类 Diadema antillarum 由疾病引起的衰退。因此，了解影响棘齿目食草动物的因素至关重要，包括觅食行为和距离、觅食的昼夜和月球周期以及棘齿目动物的密度，尤其是 E. viridis，跨越栖息地和地点。在巴拿马的圣布拉斯群岛进行的 24 小时跟踪研究，在月球周期的不同时间进行，表明在新月时，两种棘眼动物主要在夜间移动和进食，但在满月时模式相反。这些数据表明，在满月的夜晚容易受到捕食者和/或雀鲷的攻击可能是影响日粮觅食行为的重要选择力量。E. viridis 的每日移动距离（最小估计值）平均为 19 cm，E. lucunter 为 11 cm。E. viridis 的平均觅食范围估计为 D. antillarum 大小的 0.3-5%，而 E. viridis 的人均每日藻类消耗量是 D. antillarum 的 20%。这些结果表明更强烈，与 D. antillarum 相比，E. viridis 的局部放牧。对已发表的绿色 E. 密度的审查表明，50% 的研究地点（位置/栖息地组合）的密度小于 5 m-2，该水平不太可能产生强烈的食草效应。在 25% 的地点发现密度大于 15 m-2，包括圣布拉斯群岛、本研究中的巴拿马斑块礁，平均 26 m-2。在高密度与低捕食者数量相结合的情况下，绿藻会对藻类组合产生强烈的直接影响，对珊瑚和其他底栖无脊椎动物有潜在的间接影响。然而，现有的已发表数据表明，绿色 E. viridis 的丰度存在强烈的区域差异，但尚无法解释，这限制了其在整个加勒比海地区作为珊瑚礁食草动物的潜在作用。E. viridis 的形态特征可能与捕食脆弱性有关，因栖息地而异。一种新描述的黑色变种占人口的 4-16%，在不同栖息地类型的频率上有显着差异。不同栖息地的体型（测试直径）也各不相同，较大的个体在栖息地较少的栖息地中更为常见。相似地，在对捕食者提供较少保护的栖息地中，脊椎长度相对于测试直径更长。降低捕食者检测或捕食脆弱性的形态特征，以及栖息地提供的避难所，最终将影响特定珊瑚礁上的绿色 E. viridis 的数量及其在捕食者面前觅食的能力。