Galapagos Coral

Polycyathus isabela is an azooxanthellate coral, meaning that this species does not have zooxanthellae, the algae that live inside the tissues of some corals and provide the coral with food (4). Corals without zooxanthellae instead feed on zooplankton, capturing these tiny aquatic animals in their outstretched tentacles (5).

The unique biodiversity of the Galápagos Islands and the surrounding waters is recognised and valued, and thus the region is protected by being designated a Marine Reserve and World Heritage Site (1). Polycyathus isabela is also included in Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any international trade in this species should be carefully regulated (2). Unfortunately, neither of these measures protects this Vulnerable coral from the threats of natural, or man-induced, climate change.

A rare coral found only around the islands after which it is named, Polycyathus isabela generally forms low colonies in which the individual corallites are joined together (3). Corals of the Caryophylliidae family are usually pale in colour, and as this species is a rather small and cryptic coral, it is easily overlooked (3).

Polycyathus isabela can be found in dimly-lit caves and recesses, at depths between 10 and 23 metres (1).

Currently, Polycyathus isabela is known from only three sites around the island of Isabela, in the Galápagos Archipelago (1).

Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

As Polycyathus isabela has only been recorded from three sites (1), the rarity of this species is of some concern. The small population and range size of this coral makes it incredibly vulnerable to any threats that may arise. Whilst it is not clear whether Polycyathus isabela currently does face any threats, it is assumed that both El Niño and climate change could have detrimental effects on this coral (1).

Polycyathus isabela Wells, 1982

Polycyathus isabela Wells. 1982:211, pl. 1: figs. 1–3; 1983:236, pl. 14: figs. 1–3.

DESCRIPTION.—Corallum colonial, cylindrical corallites arising from thin basal encrustation, often directly adjacent to base of parent corallite. Largest corallite of holotypic colony 6.5 mm in calicular diameter and 8.1 mm tall; calice elliptical. Costae equal and slightly convex, about 0.32 mm wide, and separated by distinct intercostal striae about 0.08 mm wide. Coenosteum light brown to white; costae covered by low, coarse granules.

Septa hexamerally arranged in four incomplete cycles according to the formula S1>S2>S3>S4: a corallite with a greater calicular diameter of 2.0 mm has only 24 septa; 2.8 mm, 32 septa; 3.0 mm, 36 septa; and 3.7–6.5 mm, 42 septa. Inner edges of S1–2 straight; edges of S3 slightly sinuous; edges of S4 lacerate. Six slender, crispate, twisted P1 form a palar crown deep in fossa adjacent to columella. A second crown of six P2 each palus equal in size to a P1, occurs slightly higher in the fossa A third crown of 12 P3, each palus twice the size of a P1–2 but equally crispate, occurs still higher in fossa. Fossa moderately deep. Columella papillose, composed of 15–20 slender, irregularly shaped rods.

azooxanthellate

14-23 m

Known from seamounts and knolls