Nutritional diversity of symbiotic ascidians in a Fijian seagrass meadow

In a coastal lagoon of Dravuni Island, Fiji, at least six species of compound ascidians, some of them harboring Prochloron as symbiotic algae, were found in a Syringodium-dominated seagrass meadow. Based on their heterotrophic (filter feeding rates) and autotrophic (photosynthetic) activities, carbon gain of the ascidians was categorized into two groups: (i) supported by heterotrophic metabolism; and (ii) supported by both heterotrophic and autotrophic metabolisms. Didemnum molle, Lissoclinum bistratum and Lissoclinum voeltzkowi belong to the latter group, and the relative contribution of the autotrophic process was a significant portion of their carbon gain (52-74%). These symbiotic ascidians were found in light microhabitats, while the heterotrophic species occupied shady environments rich in suspended organic materials, such as the sheath surface of the seagrass.