Predation on a sacoglossan gastropod by a mushroom coral

Abstract

Predation on a sacoglossan gastropod by a mushroom coral Only a few documented examples are known of predation on sacoglossans, which are heterobranch sea slugs famous for ingesting the cellular contents of algae (Krug et al. 2013). Known predators of sacoglossans include, for example, species of fish and crabs (Trowbridge 1994). Information on scleractinian corals eating large-sized prey became only recently available (Hoeksema and Waheed 2012); therefore, it is not surprising that no examples have been reported on sea slugs being eaten by corals. During a field survey on a fringing reef off Sai Tong beach (10°03¢41 †N, 99°49¢30 †E) on December 22, 2014, at the island Koh Tao (Gulf of Thailand), a sacoglossan gastropod, Plakobranchus sp., was found being consumed by a monostomatous mushroom coral, Pleuractis paumotensis (Stutchbury, 1833) for 20 min (1320-1340 hrs). The coral was part of a mushroom coral assemblage on a sandy substrate (9 m depth) that is rarely visited by divers. The sea slug (~22 mm long) was already inside the coral's mouth when it was discovered (Fig. 1). It is not known whether the individual was later expelled or consumption was completed but <10 mm of its length remained by the end of observation with no signs of rejection. The present specimen belongs to the P. ocellatus species complex, which is in need of further revision (Krug et al. 2013). Around Koh Tao, Plakobranchus slugs are commonly found year-round on shallow sandy substrates (0-20 m depth) where they are optimally exposed to sunlight. The unlucky individual had probably crawled against the coral's periphery, from where it was transported toward the mouth by the coral's tentacles (see Hoeksema and Waheed 2012). Incidental observations like this one can clarify the role of corals as predators, and which prey they can consume.

Phylogenetic relationships within the Phyllidiidae (Opisthobranchia, Nudibranchia)

“…All nudibranch species and many other sea slugs are predators, which usually can be observed together with their prey ( Behrens 2005 , Pola and Gosliner 2010 , van Alphen et al 2011 ). Only rarely they are found together with potential predators such as sea anemones, mushroom corals, and pycnogonids ( Piel 1991 , Behrens 2005 , van der Meij and Reijnen 2012 , Mehrotra et al 2015 ).…”

Mobility and self-righting by a free-living mushroom coral through pulsed inflation

“…The flip side of a free mode of life is that mushroom corals may accidentally get overturned by other animals or by tumbling down-slope (Jokiel and Cowdin 1976;Hoeksema 1988;Chadwick-Furman and Loya 1992). This is unfavorable because it would incapacitate their ability to capture food, for which an upright position would be most suitable (Hoeksema and Waheed 2012;Mehrotra et al 2015).…”

On the Plakobranchidae (Gastropoda, Sacoglossa) from soft sediment habitats of Koh Tao, Gulf of Thailand, with descriptions of two new species

“…Known only from the Philippines, Malaysia, Indonesia, and Papua New Guinea (Meyers-Muñoz et al 2016; Yonow and Jensen 2018). Known from Gulf waters of Thailand (Mehrotra et al 2015).…”

“…and Plakobranchus cf. papua by Mehrotra et al (2015Mehrotra et al ( , 2019 in observations of predation. Although Plakobranchus ianthobaptus has long been considered a synonym of Plakobranchus ocellatus van Hasselt, 1824 (see Jensen 1992;Evertsen et al 2007 and others).…”