Success in Competition for Space in Two Invasive Coral Species in the western Atlantic – <i>Tubastraea micranthus</i> and <i>T</i>. <i>coccinea</i>

Invasion success by an alien species is dependent upon rate of reproduction, growth, mortality, physical characteristics of the environment, and successful competition for resources with native species. For sessile, epibenthic marine species, one critical resource is space. We examined competitive success in two invasive Indo-Pacific corals involved in competition for space in the northern Gulf of Mexico—Tubastraea coccinea and T. micranthus—on up to 13 offshore oil/gas platforms south of the Mississippi River. Still-capture photos of thousands of overgrowth interactions between the target corals and other sessile epibenthic fauna were analyzed from ROV videos collected at 8–183 m depth. T. micranthus was observed overgrowing >90% of all sessile epibenthic species which it encountered. Frequencies of competitive success varied significantly between platforms. T. coccinea was competitively superior to all competitors pooled, at the 60% level. There was little variability between T. coccinea populations. T. coccinea encountered the following species most frequently—the encrusting sponges Xestospongia sp. (with the commensal Parazoanthus catenularis), X. carbonaria, Dictyonella funicularis, Mycale carmigropila, Phorbas amaranthus, and Haliclona vansoesti—and was found to be, on average, competitively superior to them. Both T. micranthus and T. coccinea appear to be good competitors for space against these species in the northern Gulf of Mexico. Competitive success in T. micranthus was highest in the NE part of the study area, and lowest in the SW area near the Mississippi River plume. T. coccinea’s competitive success peaked in the SW study area. This suggests that variation in competitive success both within and between populations of these species may be due to differences in local environmental factors.外来物种的入侵成功率，取决于其繁殖速率、生长速度、死亡率、环境物理特征，以及与本土物种争夺资源的竞争获胜能力。对于固着底表海洋物种（sessile epibenthic marine species）而言，空间是关键限制性资源之一。 我们以墨西哥湾北部的两种入侵性印度-太平洋珊瑚——筒星珊瑚（Tubastraea coccinea，下称T. coccinea）和大杯筒星珊瑚（Tubastraea micranthus，下称T. micranthus）——为研究对象，分析它们在密西西比河以南多达13座近海油气平台上的空间竞争能力。研究团队对采集自8~183米水深的遥控水下机器人（ROV）视频中提取的数千张目标珊瑚与其他固着底表动物的覆盖互作静态照片进行了分析。 观测发现，大杯筒星珊瑚能够覆盖其所接触到的90%以上的固着底表海洋物种。不同油气平台间的竞争获胜频率存在显著差异。筒星珊瑚在合并统计的所有竞争者中占据优势，整体竞争获胜率达60%，且其不同种群间的竞争能力几乎无差异。 筒星珊瑚最常遭遇的物种包括：附生有共生丝形副海葵（Parazoanthus catenularis）的硬海绵（Xestospongia sp.）、炭色硬海绵（X. carbonaria）、绳状网海绵（Dictyonella funicularis）、刻纹肉海绵（Mycale carmigropila）、红紫柔海绵（Phorbas amaranthus）以及范氏筒海绵（Haliclona vansoesti）；平均而言，筒星珊瑚在与这些物种的竞争中均能占据优势。 在墨西哥湾北部海域，两种珊瑚均为空间竞争中的优势竞争者。其中，大杯筒星珊瑚的竞争获胜率在研究区域东北部最高，而在靠近密西西比河冲淡水羽流的西南部最低；筒星珊瑚的竞争获胜率则在研究区域西南部达到峰值。这表明，这两种珊瑚的种群内部及种群之间的竞争成功率差异，可能源于局部环境因子的差异。