Abstract
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.
Highlights
The introduction of non-native marine species on native biota has been shown to decrease diversity, cause local species extirpations, extinctions, and at the ecosystem level induce changes in community structure and function (Katsanevais et al 2014; Anton et al 2019)
In field sampling surveys conducted from April to December 2020, Ophiothela mirabilis was present on plexaurid and/or gorgoniid colonies at 18 of 22 sites, including the northernmost site surveyed near West Palm Beach (Fig. 1)
Individuals of O. mirabilis were found on 100% of colonies at three sites, were abundant at a further three, moderately common on plexaurid colonies at seven sites, moderately common on gorgoniid colonies at four sites and rare at four sites
Summary
The introduction of non-native marine species on native biota has been shown to decrease diversity, cause local species extirpations, extinctions, and at the ecosystem level induce changes in community structure and function (Katsanevais et al 2014; Anton et al 2019). Such impacts are concerning in terms of the recent acceleration in marine bioinvasions (Seebens et al 2017; Pyšek et al 2020). In just 20 years, O. mirabilis has undergone a notable range expansion of 6000 km in the
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