Division of Marine Science and Technology, The College of the Florida Keys, Key West, FL 33040, USA.
Institute of Environment, Department of Biological Sciences, Florida International University, Miami, FL 33181, USA.
Curr Biol. 2021 Feb 22;31(4):853-859.e3. doi: 10.1016/j.cub.2020.10.097. Epub 2020 Dec 10.
Coral reefs are on a steep trajectory of decline, with natural recovery in many areas unlikely. Eutrophication, overfishing, climate change, and disease have fueled the supremacy of seaweeds on reefs, particularly in the Caribbean, where many reefs have undergone an ecological phase shift so that seaweeds now dominate previously coral-rich reefs. Discovery of the powerful grazing capability of the Caribbean's largest herbivorous crab (Maguimithrax spinosissimus) led us to test the effectiveness of their grazing on seaweed removal and coral reef recovery in two experiments conducted sequentially at separate locations 15 km apart in the Florida Keys (USA). In those experiments, we transplanted crabs onto several patch reefs, leaving others as controls (n = 24 reefs total; each 10-20 m in area) and then monitored benthic cover, coral recruitment, and fish community structure on each patch reef for a year. We also compared the effectiveness of crab herbivory to scrubbing reefs by hand to remove algae. Crabs reduced the cover of seaweeds by 50%-80%, resulting in a commensurate 3-5-fold increase in coral recruitment and reef fish community abundance and diversity. Although laborious hand scrubbing of reefs also reduced algal cover, that effect was transitory unless maintained by the addition of herbivorous crabs. With the persistence of Caribbean coral reefs in the balance, our findings demonstrate that large-scale restoration that includes enhancement of invertebrate herbivores can reverse the ecological phase shift on coral reefs away from seaweed dominance.
珊瑚礁正处于急剧衰退的轨道上，许多地区的自然恢复几乎不可能。富营养化、过度捕捞、气候变化和疾病助长了海藻在珊瑚礁上的优势地位，尤其是在加勒比地区，许多珊瑚礁已经经历了生态阶段转变，海藻现在主宰了以前珊瑚丰富的珊瑚礁。发现加勒比地区最大的草食性螃蟹（Maguimithrax spinosissimus）具有强大的摄食能力，这促使我们在佛罗里达群岛（美国）相距 15 公里的两个独立地点进行的两项连续实验中，测试其摄食对海藻清除和珊瑚礁恢复的效果。在这些实验中，我们将螃蟹移植到几个斑块状珊瑚礁上，而将其他珊瑚礁作为对照（共 24 个珊瑚礁，每个珊瑚礁面积为 10-20 米），然后监测每个斑块状珊瑚礁上的底栖生物覆盖率、珊瑚补充和鱼类群落结构，为期一年。我们还比较了螃蟹草食性与手动擦洗珊瑚礁以去除藻类的效果。螃蟹将海藻的覆盖率降低了 50%-80%，导致珊瑚补充和珊瑚礁鱼类群落丰度和多样性相应增加了 3-5 倍。虽然手动擦洗珊瑚礁的劳动强度很大，但除非通过添加草食性螃蟹来维持，否则藻类覆盖率的减少是暂时的。由于加勒比珊瑚礁的持续存在处于平衡之中，我们的研究结果表明，包括增强无脊椎动物草食性动物在内的大规模恢复可以扭转珊瑚礁上海藻优势的生态阶段转变。
