Assessment of tunicates found in the northern waters of Ambon Island and its rearing requirements in a laboratory setting

Abstract

The Banda Sea region is situated in the Wallacea biogeographical area, known as one of the biodiversity hotspots of the world. The region harbours various types of ecosystems, ranging from mangroves and coral reefs to seaweeds, indicating its potential for harbouring organisms that produce bioactive compounds, such as sea cucumbers, soft corals, and tunicates. While many studies have been carried out on the first two organisms, much lesser is known about the latter one, notably in this region. The assessment is our first attempt to explore the tunicates found in northern coastal waters of Ambon Island, an area that is a part of the Banda Sea. Two types of tunicates were obtained during the survey, namely the violet-green and white-yellow variants of solitary tunicates Polycarpa aurata (15 specimens) and social ones of Didemnum molle (3 specimens). The Polycarpa specimens’ heights ranged from 2.5 to 4.8 cm with wet weights from 9.4 to 28.03 g, and the Didemnum ones were of 1.2 - 2 cm and wet weights from 1.2 to 5 g. Feeding experiment indicated that low volume (5-10 ml) of pure cultures such as Dunaliella sp., Nannochloropsis sp. and Tetraselmis sp. in small aquarium (40 x 60 cm) resulted in good survival rate for Polycarpa aurata collected from northern Ambon Island waters. Rearing experiments in a discontinuous aquarium setting using solitary tunicates indicated the following requirements: thorough cleaning of the tanks, regular feeding intervals, and regular cleaning of each tunicate. The regular cleaning of mucous at the external part of tunicates is indispensable to ensure the wellbeing of the organisms.