Antipredatory escape behaviors of two benthic ctenophores in South Florida

Benthic ctenophores, members of the family Coeloplanidae (Order Platyctenida, Phylum Ctenophora) are more widespread and abundant in tropical and subtropical marine environments than formerly recognized. Coeloplanid ctenophores are members of the most speciose family of benthic ctenophores, with 33 recognized species of Coeloplana and one species of the genus Vallicula (Mills 1998). The majority of coeloplanids are ectosymbionts of algae and diverse benthic invertebrates (Matsumoto 1999, Alamaru et al. 2015, 2017). Hundreds to thousands of individuals can occupy preferred habitats in <1 m2 of substrate patches. Galt (1998) noted Vallicula multiformis inhabiting algae in Hawaii at population densities as high as 10,000 individuals/m2. Also, in South Florida Glynn et al. (2017) observed 100s of individuals of V. multiformis inhabiting macroalgae, and 1,000 to 1,500 individuals of Coeloplana waltoni on octocoral stems. Like many of their pelagic counterparts, benthic ctenophores are efficient predators, employing a pair of extensible tentacles with numerous short tentilla (side‐branches) armed with colloblasts (sticky cells) that assist in prey capture. When fishing, the tentacles can extend to at least 5–10 times the body length, capturing mesozooplankton, both holoplankton and meroplankton. These planktonic components often include fish eggs and larvae (Glynn et al. 2018), both of which play a crucial role in population counts of many species. Studies have generally focused on the predatory behavior of benthic ctenophores with the functional role of tentacles involved in the capture of zooplankton (Rankin 1956, Emson and Whitfield 1991, Eeckhaut et al. 1997). However, recent observations have shown that tentacles may serve an alternative purpose. Here, we offer behavioral and photographic evidence that coeloplanid tentacles may also function defensively in protection against predators. Here, we describe the defensive behaviors of Vallicula multiformis Rankin 1956 and Coeloplana waltoni Glynn et al. (2014). Vallicula multiformis occurs in shallow (0.25–2.0 m depth), sheltered biofouling communities, commonly ranges 2–8 mm in body length, and often assumes the color of its biotic host. Coeloplana waltoni occurs at 2–10 m depth on octocorals in exposed coastal habitats, is 1–2 mm in body length, translucent, and notably cryptic. Both ctenophore species inhabit species‐rich communities with numerous potential predators and competitors. Two types of ctenophore defensive behaviors are herein described, the extension of compact tentacle tangles by V.