Microbial aggregates within tissues infect a diversity of corals throughout the Indo-Pacific

Abstract

Coral reefs are highly diverse eco - systems where symbioses play a pivotal role. Corals contain cell-associated microbial aggregates (CAMA), yet little is known about how widespread they are among coral species or the nature of the symbio tic re- lationship. Using histology, we found CAMA within 24 species of corals from 6 genera from Hawaii, American Samoa, Palmyra, Johnston Atoll, Guam, and Australia. Prevalence (%) of infection varied among coral genera: Acropora, Porites, and Pocillo- pora were commonly infected whereas Montipora were not. Acropora from the Western Pacific were significantly more likely to be infected with CAMA than those from the Central Pacific, whereas the re- verse was true for Porites. Compared with apparently healthy colonies, tissues from diseased colonies were significantly more likely to have both surface and basal body walls infected. The close association of CAMA with host cells in numerous species of appar- ently healthy corals and lack of associated cell patho - logy reveals an intimate agenthost association. Fur- thermore, CAMA are Gram negative and in some corals may be related to chla mydia or rickettsia. We propose that CAMA in adult corals are facultative secondary symbionts that could play an important ecological role in some dominant coral genera in the Indo-Pacific. CAMA are important in the life histories of other animals, and more work is needed to under- stand their role in the dis tribution, evolution, physio - logy, and immunology of reef corals.