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Abstract
The colonial ascidian Didemnum vexillum has become relatively widespread in New Zealand, since its initial discovery in 2001. Despite the potential economic and ecological impacts of D. vexillum, there are still considerable knowledge gaps surrounding its key biological attributes. The ability to obtain larvae and culture colonies in the laboratory is crucial to research into larval longevity and dispersal potential, and the factors affecting colony survivorship and growth. Here we present methods for spawning and culture of D. vexillum under laboratory conditions. A ‘light shocking without cycles’ technique was used to stimulate larval release in adult colonies, with > 500 larvae being produced from ~ 100 g of tissue at the peak of the reproductive season. Following release, the larvae were allowed to metamorphose and the juveniles were cultured under controlled conditions for four weeks. Recruit survival during the four weeks of culture was > 85 % with the majority having formed small colonies of 4 to 6 zooids with a dense cover of white spicules throughout the tunic. The most effective laboratory spawning conditions are described with respect to light and temperature. The ability to obtain D. vexillum larvae on demand will enable increased research into several aspects of this species’ reproductive biology and ecology.
Highlights
The ongoing human-mediated spread of nonindigenous ascidian species is causing growing concern globally (Lambert 2001; Carver et al 2003; G. Lambert 2005; LeBlanc et al 2007)
Research on larval longevity will aid our understanding of ascidian dispersal potential, as this is heavily dependent on the initial planktonic phase of the life history
The present study documents procedures we have recently developed to successfully induce spawning in D. vexillum colonies, as well as techniques for the successful settlement and metamorphosis of the larvae, and culture of the juvenile recruits
Summary
The ongoing human-mediated spread of nonindigenous ascidian species is causing growing concern globally (Lambert 2001; Carver et al 2003; G. Lambert 2005; LeBlanc et al 2007). Research into the factors affecting colony survivorship, growth and the potential spread of this species is still relatively scarce (but see Daniel and Therriault 2007). A range of abiotic and biotic factors that affect both the larval and post-settlement life-stages have been shown to dramatically influence subsequent adult populations In order to better understand the factors controlling the distribution and persistence of D. vexillum, increased research on the early life-stages (i.e., larvae and newly settled juveniles) is required. Knowledge of the environmental conditions that favour ascidian larvae and juveniles may be applied when predicting areas susceptible to new invasions or range expansions (Epelbaum et al 2009a)
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