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Skeletal Eroding Band

Skeletal Eroding Band (SEB) is characterized by the destruction of the surface layer of coral skeleton by ciliates which settle as larvae into the skeleton and slowly break it into splinters as the ciliates grow their loricae. To date it has been observed only in the Indo-Pacific from studies in Papua New Guinea from Motupore Island, Australia at Lizard Island, Mauritius, Sinai, and most recently was discovered in the Red Sea's Gulf of Aqaba.

Appearance

It appears as a black-grey band of the aggregating ciliates. In the field it can easily be mistaken for Black Band Disease (BBD), but unlike BBD and other coral diseases that typically harm only the coral tissue, SEB destroys the coral's trabecular limestone skeleton. While BBD will migrate along the coral and leave a clean white skeleton, SEB will leave a skeleton dotted with the empty loricae of ciliates to give it a "dirty" appearance.

Composition

The culprit of SEB is the Folliculinid ciliate Halofolliculina corallasia of the family Folliculinidae. The ciliate is a sessile protist that secretes a bottle-like housing called a lorica, the neck of which usually only rises above the surface of the coral. The ciliates embed themselves into the skeleton of the coral and aggregate in densities as 417 individuals per mm². The ciliates produce new individuals through cell division as a migratory larval stage, which usually settle close to SE-band on living coral and secrete loricae. The unhardened loricae have organic acid associated with them, and in addition to the rapid spinning behavior of the larvae is responsible for the destruction of the coral skeleton's surface layer. The band of individuals can migrate at rates from 1 mm per week to 1 mm per day, similar to that of Black Band Disease.