Info
Dr. Bo has taken this photo in the Bunaken Marine Park in North Sulawesi, Indonesia, between 20 and 30 m depth, the water temperature was around 26 °C.
Black corals normaly feed on zooplankton, but not exclusively!
Have a brief look to the publications underneath this information:
https://www.researchgate.net/publication/256487019_First_description_of_algal_mutualistic_endosymbiosis_in_a_black_coral_Anthozoa_Antipitharia
First description of algal mutualistic endosymbiosis in a black coral (Anthozoa: Antipitharia)
http://rspb.royalsocietypublishing.org/content/early/2010/10/19/rspb.2010.1681
Azooxanthellate? Most Hawaiiian black corals contain Symbiodinium!
Synonym: Antipathes myriophylla Pallas, 1766