Cabanillas-Terán Nancy, Loor-Andrade Peggy, Rodríguez-Barreras Ruber, Cortés Jorge
Departamento Central de Investigación, Universidad Laica Eloy Alfaro de Manabí , Ciudadela Universitaria. Vía San Mateo, Manta, Manabí , Ecuador.
Department of Biology, University of Puerto Rico at Bayamón , Puerto Rico.
PeerJ. 2016 Jan 14;4:e1578. doi: 10.7717/peerj.1578. eCollection 2016.
Sea urchins are important grazers and influence reef development in the Eastern Tropical Pacific (ETP). Diadema mexicanum and Eucidaris thouarsii are the most important sea urchins on the Ecuadorian coastal reefs. This study provided a trophic scenario for these two species of echinoids in the coral-rocky reef bottoms of the Ecuadorian coast, using stable isotopes. We evaluated the relative proportion of algal resources assimilated, and trophic niche of the two sea urchins in the most southern coral-rocky reefs of the ETP in two sites with different disturbance level. Bayesian models were used to estimate the contribution of algal sources, niche breadth, and trophic overlap between the two species. The sea urchins behaved as opportunistic feeders, although they showed differential resource assimilation. Eucidaris thouarsii is the dominant species in disturbed environments; likewise, their niche amplitude was broader than that of D. mexicanum when conditions were not optimal. However, there was no niche overlap between the species. The Stable Isotope Analysis in R (SIAR) indicated that both sea urchins shared limiting resources in the disturbed area, mainly Dictyota spp. (contributions of up to 85% for D. mexicanum and up to 75% for E. thouarsii). The Stable Isotope Bayesian Ellipses in R (SIBER) analysis results indicated less interspecific competition in the undisturbed site. Our results suggested a trophic niche partitioning between sympatric sea urchin species in coastal areas of the ETP, but the limitation of resources could lead to trophic overlap and stronger habitat degradation.
海胆是重要的食草动物，对东热带太平洋（ETP）的珊瑚礁发育有影响。墨西哥冠海胆和杜氏长海胆是厄瓜多尔沿海珊瑚礁上最重要的海胆。本研究利用稳定同位素为厄瓜多尔海岸珊瑚 - 岩石礁底部的这两种海胆类动物提供了一个营养状况图景。我们评估了这两种海胆在ETP最南部珊瑚 - 岩石礁的两个不同干扰水平地点所同化的藻类资源的相对比例以及营养生态位。使用贝叶斯模型来估计藻类来源的贡献、生态位宽度以及这两个物种之间的营养重叠。海胆表现为机会主义觅食者，尽管它们在资源同化方面存在差异。杜氏长海胆是受干扰环境中的优势物种；同样，在条件不理想时，它们的生态位幅度比墨西哥冠海胆更宽。然而，这两个物种之间不存在生态位重叠。R语言中的稳定同位素分析（SIAR）表明，在受干扰区域，两种海胆共享有限的资源，主要是网胰藻属物种（墨西哥冠海胆的贡献率高达85%，杜氏长海胆高达75%）。R语言中的稳定同位素贝叶斯椭圆分析（SIBER）结果表明，在未受干扰的地点种间竞争较少。我们的研究结果表明，ETP沿海地区同域分布的海胆物种之间存在营养生态位划分，但资源限制可能导致营养重叠和更强的栖息地退化。
