Collection and Handling of Prochloron and Its Ascidian Hosts
Though its unique features were recognized only recently, Prochloron—the only marine prokaryote that photosynthesizes by using a chlorophyll a+b system like that of land plants—is not a rare alga on many tropical seashores. Like the zooxanthellae of corals, it exists as a symbiont in zones where other algae are sparse or absent. We have found it especially abundant in low-littoral to sublittoral zones around Palau, in the West Caroline Islands, where at least six species of didemnids (colonial ascidians), occupying dissimilar and distinct ecological niches, harbor this prochlorophyte symbiont. Massed colonies of one of these hosts, Trididemnum cyclops, cover a large proportion of the exposed surfaces 1 or 2 m below mean sea level off Kamori island, in a swath several meters wide and several hundred meters long; its biomass maybe conservatively estimated at 0.1 tons (wet weight), of which at least 10 kg is represented by Prochloron. Per unit area, the chlorophyll a and b contents of such areas of symbiotic didemnids, and presumably therefore the productivity of the Prochloron, are comparable to those of, say, a field of grass or the phytoplankton in a column of reasonably fertile water.
KeywordsAlgal Cell Dead Coral Symbiotic Alga Sublittoral Zone Host Coloni
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