Widespread and large populations of the non-native eastern Pacific ophiuroid brittle star Ophiothela mirabilis now occur in southeastern Florida, extending the range of this recently introduced species from southern Brazil northward to the eastern Caribbean Sea and Florida. The Florida brittle stars, representing two lineages, are epibionts on shallow (3–18 m depth), tropical/subtropical plexaurid (e.g., Eunicea spp., Muricea spp.) and gorgoniid (Antillogorgia spp.) octocorals. The scope of this study includes recent distributional records of O. mirabilis in south Florida, field abundances in relation to the cohabiting endemic ctenophore Coeloplana waltoni, behavioral observations of the ophiuroid, ctenophore and the predatory amphipod Caprella penantis, as well as a laboratory experiment testing the effects of the non-native ophiuroid on the native ctenophore. Individuals of O. mirabilis have been collected near St. Lucie Inlet, extending its northern-most range by about 110 km since 2019. Two years of field sampling have demonstrated significant declines of the native, benthic ctenophore with increasing abundances of the non-native ophiuroid. Evidence suggests that the ophiuroid is negatively affecting the abundances of the ctenophore through interference competition, greatly aided by its abrasive armature of calcareous spines, plates and hooks. This detrimental effect justifies considering O. mirabilis as an invasive species in south Florida. Sporadic and intense predation by a caprellid amphipod also probably contributes to the ctenophore’s decline, but to a lesser extent than that caused by the ophiuroid. Adding to the risk of extinction of C. waltoni is its narrow requirement of living octocorals as hosts and restricted distribution in southeast Florida and the Bahamas.

非原生的东太平洋类鸦片类脆性星Ophiothela mirabilis 的广泛和大量种群现在出现在佛罗里达州东南部，将这种最近引入的物种的范围从巴西南部向北扩展到加勒比海东部和佛罗里达州。佛罗里达脆性星代表两个谱系，是浅层（3-18 m 深）、热带/亚热带丛珊瑚（例如Eunicea spp.、Muricea spp.）和 Gorgoniid（Antillogorgia spp.）八珊瑚上的表生生物。本研究的范围包括南佛罗里达州奇异果的最近分布记录、与同居的地方性栉水母Coeloplana waltoni相关的野外丰度，对 ophiuroid、栉水母和掠食性片脚类Caprella penantis 的行为观察，以及测试非本地 ophiuroid 对本地栉水母的影响的实验室实验。O. mirabilis 的个体在圣露西湾附近被采集，自 2019 年以来，其最北端的范围扩大了约 110 公里。两年的实地采样表明，随着非原生底栖栉水母丰度的增加，原生底栖栉水母数量显着减少类鸦片。有证据表明，鸦片类通过干扰竞争对栉水母的丰度产生负面影响，这极大地得益于其钙质棘、板和钩的磨蚀骨架。这种不利影响证明考虑O. mirabilis作为南佛罗里达州的入侵物种。caprellid 片脚类的零星和强烈的捕食也可能导致栉水母的衰退，但程度低于由鸦片类动物引起的。增加C. waltoni灭绝的风险是它对活八珊瑚作为寄主的狭隘需求以及在佛罗里达东南部和巴哈马的有限分布。