Benthic ctenophores (Platyctenida: Coeloplanidae) in South Florida: predator–prey interactions

Abstract

The primary goal of this study was to demonstrate, from field observations and laboratory experiments, some key trophic roles of benthic ctenophores as predators and prey in subtropical communities. We examined individuals of two benthic platyctenid species: Coeloplana waltoni, a minute epibiont on octocorals in exposed, open‐water settings; and Vallicula multiformis, an associate of calm‐water biofouling communities and floating Sargassum spp. Laboratory observations of individuals of both ctenophore species revealed frequent capture and ingestion of diverse zooplankton taxa, especially crustaceans. Laboratory predation trials demonstrated the capture of dolphinfish (Coryphaena hippurus) eggs and larvae by both ctenophore species. Dolphinfish eggs and larvae larger than individuals of C. waltoni were captured but not ingested during 2‐h trial periods. These prey items were sometimes purloined and ingested by polyps of the ctenophore's octocoral host. Ingestion of dolphinfish eggs and larvae by individuals of C. waltoni was observed, however, after longer periods of exposure to prey. In predation trials, dolphinfish eggs and larvae were both captured and ingested by larger individuals of the ctenophore species V. multiformis. Field and laboratory observations revealed diverse invertebrate and fish taxa that prey on both ctenophore species. In the laboratory, the mean daily per capita consumption of individuals of C. waltoni by a pomacanthid fish ranged 0.5–2.8 individuals, and ranged 2.6–3.6 individuals for predation by an ovulid mollusc. Field population densities of these predators ranged 0.1–0.7 individuals per m2 for the pomacanthid, and 0.2–1.1 individuals per m2 for the mollusc. Laboratory feeding observations demonstrated frequent consumption of individuals of V. multiformis by a sea anemone, and by three species of brachyuran crabs. Field observations revealed eight fishes that probably feed incidentally on individuals of V. multiformis. These findings add to the limited knowledge base of predator–prey dynamics in both C. waltoni and V. multiformis.

Exotic Brittle Star Interactions With Native Octocoral Epizoites: An Endemic Benthic Ctenophore in Peril?

“…Bavestrello et al (1996) observed caprellids seizing previously captured nauplii from hydroid polyps; a nudibranch grazing preferentially on hydroid polyps that previously ingested zooplankton, an example of the consumption of a prey item plus its ingested prey, was termed kleptopredation by Willis et al (2017). The symbiotic status of the benthic ctenophore and its octocoral host is not clear since we have observed the ctenophore purloining food (unidenti ed organic detritus) captured by its host's polyps, and octocoral polyps have been observed removing captured sh eggs from the tentacles of ctenophore epizoites (Glynn et al 2018a). Further study is necessary to determine the signi cance of these trophic resources, the relative amounts garnered by the symbiotic partners, and how eld conditions affect these interactions.…”

“…Since octocorals engage heavily in suspension feeding, capturing particulate organic matter (Lasker, 1981) and microzooplankton (Glynn et al 2018a), the interference of polyp expansion by individuals of O. mirabilis was suggested to be a potentially signi cant threat against satisfying the trophic requirements of octocoral hosts (Araújo et al 2018;Ferry et al 2020), although a recent study suggests this may not be consequential (Glynn et al, 2021). From the current study --which has demonstrated an inverse relationship in the abundance of ophiuroids and ctenophores in eld collections, and decreasing ctenophore abundance in the presence of ophiuroids in a laboratory experiment --it appears that the major effect of the exotic ophiuroid is on the displacement, by interference competition, of the cohabiting benthic ctenophore.…”

Benthic ctenophore (Order Platyctenida) reproduction, recruitment, and seasonality in south Florida

“…This possibility is in need of further investigation. Sporadic declines of V. multiformis are possibly related to predation (Glynn et al, ) or low organic production and a scarcity of trophic (zooplankton) resources. Alamaru et al () reported maximum abundances of V. multiformis in the Gulf of Aqaba (Red Sea) in the winter season during water column mixing and massive algal blooms.…”

Antipredatory escape behaviors of two benthic ctenophores in South Florida

“…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.…”

“…Agitation or predator simulation was effected by pricking ctenophores, dislodging them from a resting position by forceful water jets, and probing with a cheliped of a known crab predator [Portunus sayi (Gibbes 1850)]. Additionally, naturally occurring live predators of V. multiformis, the sea anemone Exaiptasia pallida (Agassiz in Verrill, 1864), and of C. waltoni, the gastropod mollusk Cyphoma gibbosum Linnaeus 1758 and the pygmy angelfish Centropyge argi Woods & Kanazawa 1951, were offered ctenophore prey (see Glynn et al 2018 Individuals of V. multiformis remained motionless under low light and low flow to still water conditions. In feeding trials, tentacle extension occurred in a matter of minutes in flowing water with zooplankton.…”