Ctenactis crassa - Mabini, Provinz Batangas, Philippinen

Ctenactis crassa - El Qoseir, Red Sea Governorate, Ägypten

Ctenactis crassa - Ras Mohammed National Park, EG-JS-SS, EG-JS, EG

Ctenactis crassa - Biorock, Pemuteran, Bali, Indonesia

Ctenactis crassa - Magari, Kumejima, Shimajiri-Gun, Okinawa, JP

Ctenactis crassa - Mansuar Is, Raja Ampat Regency, West Papua, Indonesia

Ctenactis crassa - F884+PXG, Rawai, Mueang Phuket District, Phuket, Thailand

Ctenactis crassa - Marsa Alam, Red Sea Governorate, Egypt

Ctenactis crassa - Marsa Shagra Halaib W Shalatin، 22km North، Marsa Alam, Red Sea Governorate 84712, Egypt

Ctenactis crassa - Gunung Bagahak, Lahad Datu, Sabah, Malaysia

Invertebrate · Stinging · Hard corals

Thick Tongue Coral

Ctenactis crassa (Dana, 1846)

syn. Fungia (Ctenactis) simplex, Fungia brachystoma, Fungia crassa, Fungia simplex, Haliglossa echinata var. platystoma, Herpetoglossa simplex +2 more

up to 48 cm1-31 mCITES IILeast Concern

952

This is one animal. One polyp, up to 48 cm long, lying loose on the sand and cemented to nothing.

Almost every other stony coral on the reef is a colony: thousands of small polyps, all clones, all fixed to the rock. Mushroom corals went the other way. A Ctenactis begins life as a tiny polyp on a stalk, attached to hard bottom. Then it dissolves its own skeleton along a clean plane just below the disc, breaks free, and spends the rest of its life unattached. The stump left behind can bud a replacement, and another after that.

Lying loose has a cost. Sand slides, storms and clumsy fins turn these corals over, and a mushroom coral face down in sediment suffocates. So they move. By pumping water in and out of the tissue in slow rhythmic pulses, a free-living fungiid can shuffle across the bottom and flip itself upright. In the closely related tongue coral, time-lapse recorded a complete righting in about six hours.

To identify it, look at the mouths. The disc is an elongate oval, pale brown, with an axial furrow running almost its full length, and several mouths are spaced along that furrow with none outside it. Ctenactis echinata, the commoner relative, has a single central mouth instead; the tongue coral Herpolitha limax has mouths scattered over the disc as well as in the furrow. Fungiids are genuinely hard, borderline cases need the dry skeleton in hand, and a photograph of a sand-dusted disc often will not settle the question.

It lies on sandy lagoon floors and on reef slopes sheltered from surge, from about 1 m down to 30 m, often along the line where reef meets sand, and on the Egyptian coast it is a regular sight rather than a find. Like most reef corals it grows algae in its tissue and feeds itself as well, putting out tentacles after dark. One more thing about the genus: individuals of Ctenactis echinata have been recorded changing sex back and forth, male one season and female the next.

How to recognise it

a single elongate oval disc lying loose on the bottom
an axial furrow running almost the whole length
several mouths spaced along the furrow and none outside it
pale brown, with low rows of teeth across the upper surface
up to 48 cm long

Why it's threatened

Residential & commercial development

Housing & urban areas · Commercial & industrial areas · Tourism & recreation areas

Transportation & service corridors

Shipping lanes

Human intrusions & disturbance

Recreational activities

Invasive species, genes & disease

Unspecified species

Pollution

Type Unknown/Unrecorded · Soil erosion, sedimentation · Ozone

Climate change & severe weather

Temperature extremes · Storms & flooding

This species is moderately susceptible to bleaching. In Thailand, bleaching appeared to be very common, including in this species (Hoeksema et al. 2012). Bleaching has been observed in this species in the Spratly (Nansha) Islands (Li et al. 2011) and some limited bleaching has been observed in Singapore (Ng et al. 2020).

The most critical threat for this species, like for most coral species, is the extensive degradation and reduction of coral-reef habitat because of a combination of local and global threats (Hughes et al. 2017, Hoegh-Guldberg et al. 2017, Donovan et al. 2021). The increasing threats from climate change are being further compounded by additional local stressors, such as pollution and overfishing (Knowlton and Jackson 2008, Lamb et al. 2018, MacNeil et al. 2019, Donovan et al. 2021).

Generally, the biggest threat to the persistence of corals is climate change (Hoegh-Guldberg et al. 2017, Hughes et al. 2017, Sully et al. 2019), and more specifically - ocean warming and marine heatwaves that are leading to an increase in the frequency and intensity of events of anomalously high water temperatures (Hoegh-Guldberg et al. 2019, Laufkötter et al. 2020). Under anomalously high temperatures, the symbiotic relationship between corals and their photosynthetic symbionts is disrupted, and many corals begin to bleach (Glynn 1996, Hoegh-Guldberg et al. 1999, Warner et al. 1999, Loya et al. 2001). Mass bleaching events resulting from thermal stress have become increasingly common in the last two decades and may lead to widespread coral mortality and changes in overall reef community over large areas (Loya et al. 2001, Graham et al. 2015, Hughes et al. 2018, Safaie et al. 2018, Stuart-Smith et al. 2018, McClanahan et al. 2019, Sully et al. 2019).

Superimposed on thermal stress and bleaching are additional stressors that can either directly threaten corals or exacerbate coral mortality after thermal stress (Kennedy et al. 2013, MacNeil et al. 2019, Abelson et al. 2020, Donovan et al. 2021, Knowlton et al. 2021). For example, increasing number of storms per season, overfishing, high levels of nutrients, and other kinds of pollution are steadily increasing in magnitude and threatening coral reefs (Wiedenmann et al. 2013, Zaneveld et al. 2016, MacNeil et al. 2019, Donovan et al. 2020). Moreover, in some localities, increased amounts of outbreaks of the corallivorous sea star, crown of thorns, can cause substantial damage to the reef, contributing to the overall decline and reef destruction (Saponari et al. 2015, Pratchett et al. 2017).

The prevalence of coral disease is also rising (Aronson and Precht 2001, Rosenberg and Loya 2004, Sutherland et al. 2004, Weil et al. 2012, Maynard et al. 2015), especially in the Caribbean (Aronson and Precht 2001, Precht et al. 2016, Aeby et al. 2019, Alvarez-Filip et al. 2019, Muller et al. 2020). The increasing spatial spread and extent of diseases are associated with ocean warming (Muller et al. 2008, Ruiz-Moreno et al. 2012, Randall and van Woesik 2015) and additional anthropogenic stressors (Vega Thurber et al. 2014, Maynard et al. 2015). The escalating impacts of global warming alongside the ongoing increases in local anthropogenic stressors and diseases are causing fundamental changes to coral reefs and place entire reef systems at a high risk of collapse.