Aims:  To determine the relationship between yellow band disease (YBD)‐associated pathogenic bacteria found in both Caribbean and Indo‐Pacific reefs, and the virulence of these pathogens. YBD is one of the most significant coral diseases of the tropics. Materials and Results:  The consortium of four Vibrio species was isolated from YBD tissue on Indo‐Pacific corals: Vibrio rotiferianus, Vibrio harveyi, Vibrio alginolyticus and Vibrio proteolyticus. This consortium affects Symbiodinium (zooxanthellae) in hospite causing symbiotic algal cell dysfunction and disorganization of algal thylakoid membrane‐bound compartment from corals in both field and laboratory. Infected corals have decreased zooxanthella cell division compared with the healthy corals. Vibrios isolated from diseased Diploastrea heliopora, Fungia spp. and Herpolitha spp. of reef‐building corals display pale yellow lesions, which are similar to those found on Caribbean Montastraea spp. with YBD. Conclusions:  The Vibrio consortium found in YBD‐infected corals in the Caribbean are close genetic relatives to those in the Indo‐Pacific. The consortium directly attacks Symbiodinium spp. (zooxanthellae) within gastrodermal tissues, causing degenerated and deformed organelles, and depleted photosynthetic pigments in vitro and in situ. Infected Fungia spp. have decreased cell division compared with the healthy zooxanthellae: 4·9%vs 1·9%, (P ≥ 0·0024), and in D. heliopora from 4·7% to 0·7% (P ≥ 0·002). Significance and Impact of the Study:  Pathogen virulence has major impacts on the survival of these important reef‐building corals around the tropics.

Ianthella basta marine sponges in Kimbe Bay, west New Britain, Papua New Guinea were affected by a disease, and exhibited high mortality, between 1996 and 2000. These fan-shaped sponges were mottled with brown lesions, rotted tissue and large holes. The decayed tissue was surrounded by brown biofilm that smothered the ostia openings. Since 1996, I. basta suffered its highest mortality at 3 sites within 16-20 km of the shore of west New Britain. No mortality was observed at 3 other locations further from shore (between 27-41 km), nor at 10 sites located more than 41 km from shore outside of Kimbe Bay in deeper waters, nor at the site nearest to shore. Comparison of the carbon source utilization patterns of 99 bacterial isolates from all healthy and diseased sponges revealed 5 species of bacteria specifically present in diseased I. basta. These bacteria were not present in healthy sponge samples. Bacteria isolated from affected sponges and inoculated onto healthy sponges caused disease signs similar to those in field specimens. The 16S rRNA genes from these bacteria were sequenced and found to correspond with 2 species of Bacillus and 3 species of Pseudomonas. The closest relatives of these bacteria based on BLAST searches included many terrestrial pathogens and species that are used as pathogens against insects and fungi in integrated pest control management. The bacteria causing disease in I. basta may thus originate from pesticides applied to agricultural land, predominantly oil palm plantations, in west New Britain. The possibility that these bacteria can pass virulence factors to marine bacteria through horizontal gene transfer needs to be investigated, as this may have unexpected impacts on marine ecosystems.

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