Predation on a sacoglossan gastropod by a mushroom coral
0 B. W. Hoeksema Department of Marine Zoology, Naturalis Biodiversity Center , P.O. Box 9517, 2300 RA Leiden , The Netherlands
Predation on a sacoglossan gastropod by a mushroom coral R. Mehrotra (&) C. M. Scott J. M. Rohrer New Heaven Reef Conservation Program, 48 Moo 3Koh Tao, Suratthani 84360, Thailand e-mail:
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Fig. 1 Successive stages of a Pleuractis paumotensis coral ingesting a
sacoglossan, Plakobranchus sp. (partially consumed; length ~22 mm), at Koh Tao,
Gulf of Thailand. a Part of the corals oral surface with the gastropod already
inside the mouth (1322 hrs). b Mouth of coral becoming wider (1323 hrs). c The
sea slug becoming swallowed (1324 hrs)
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 0341N,
99 4930E) 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 (13201340 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 corals
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 (020 m depth) where they are optimally exposed to sunlight.
The unlucky individual had probably crawled against the corals
periphery, from where it was transported toward the mouth by the corals
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.
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