Culturing the solitary ascidian Phallusia nigra in closed and open water systems for tropical environmental research

Abstract

Marine and coastal ecosystems have been undergoing dramatic shifts due to global environmental changes. The rise in seawater temperature, ocean acidification, hypoxia, eutrophication, and anthropogenic pollution severely affects marine organisms. There is an urgent need to better understand the influence of such disturbances on the physiology and life cycles of marine organisms. However, conducting controlled laboratory experiments often requires many replicates and information on individual origin, age, and genetic diversity. The availability of tropical model organisms is limited. Large-scale sampling efforts from wild communities may negatively impact local biodiversity, especially in coral-reef regions under threat. In this study, we present new methodologies for cultivating the tropical-origin ascidian (phylum: Chordata, class: Ascidiacea) Phallusia nigra in both closed and open water facilities, demonstrating feasibility to produce viable populations of juvenile P. nigra originating from the South China Sea (Singapore) and the Mediterranean and Red Sea coasts of Israel for research. In an open water system, P. nigra can be reared from eggs to adults for 11 months. Reproductive animals were obtained by the fourth month. As it is possible to rear individuals to maturity, long-term and cross-generational effect studies can also be explored. Finally, our work provides a method to produce a tropical model for biomedical research, which in regard to ascidians has so far been restricted to temperate cultivars. P. nigra offers fundamental opportunities for environmental research due to its wide global distribution, easy field sampling, and potential as a biological indicator species for anthropogenic pollution and global climate change.