Botrylloides violaceus
(violet tunicate)

B. violaceus is a compound ascidian (tunicate or sea squirt) and belongs to the subfamily Botryllinae. It is made up of individual genetically identical zooids and ampullae that are connected by an internal vascular system. Like all colonial ascidians, it has two types of reproduction: asexual reproduction, a process known as blastogenesis, and sexual reproduction.

It is native to the west Pacific, and is now found in the Northeast Pacific (Alaska, British Columbia to Ensenada, Baja California; Lambert and Sanamyan, 2001; Cohen et al., 2005), Sydney Harbour, Australia, the Venetian Lagoon, the Netherlands, and the coast of Japan. It can tolerate a wide range of environmental factors including temperature, salinity and nutrients (Carman et al., 2007; Dijkstra et al., 2008).  B. violaceus overgrows shellfish (e.g. mussels) and other sessile invertebrate species. It is a pest to mussel farmers and must be removed either manually or by innovative engineering.

Genetics

For information on the genetics of this species see Lejeusne et al. (2011).

Reproductive Biology

Like all colonial ascidians, B. violaceus has two types of reproduction: asexual reproduction, a process known as blastogenesis, and sexual reproduction. Asexual reproduction occurs through budding which produces colonies of genetically identical zooids. Studies have shown that small substrates limit asexual reproduction and induce sexual reproduction. B. violaceus is a hermaphrodite that undergoes sexual reproduction between 10 and 12°C. Sexual reproduction begins when the gonads of both sexes develop on either side of the zooid with the ovary situated behind the testis. The egg is ovulated in a brood pouch that forms as an outgrowth of the body wall. Within the brood pouch, the egg is fertilized and develops until the larva escapes. The brooding period depends on several factors including temperature, salinity and number of asexual reproductive cycles (Sabbadin, 1955; Millar, 1971). More on growth and reproductive cycles can be found in Yamaguchi (1975). Brown et al. (2009) report further on whole body regeneration in this species.

Larvae, when release, are relatively large (0.01-0.02 mm) and are brightly coloured. They are lecithotrophic and spend less than 24 hours in the water column before settling on suitable substrate and metamorphosing into adult colonies. During metamorphosis, the larvae sticks to the substrate and begins to form a circle of ampullae. All Botrylliodes of the same generation appear, grow, and die synchronously. Both the zooids bearing embryos and the sterile zooids of the oldest generation begin to disintegrate and are eventually reabsorbed into the common vascular system.

Environmental Requirements

B. violaceus can tolerate a wide range of environmental factors including temperature, salinity and nutrients (Carman et al., 2007; Dijkstra et al., 2008). 

Associations

B. violaceus overgrows shellfish (e.g., mussels) and other sessile invertebrate species.

23/10/08 Original text by:

Jenn Dijkstra, University of New Hampshire, USA