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Abstract
The colonial ascidian Didemnum vexillum has dispersed from its native Japan to many temperate coastal regions of the world, yet many features of its life history remain poorly studied. Using D. vexillum populations in the northeastern USA, several features of growth and sexual reproduction, as well as asexual reproduction via the unusual feature of detachment of larva-laden tendrils were examined from 2008 to 2011. Recruits of D. vexillum grown on PVC pan- els in Groton, CT, between July and September 2011 reached sexual maturity in 50 to 62 d. A nat- ural, overwintering D. vexillum population in Noank, CT, sampled weekly from 12 May to 14 July 2008 first had reproductive structures on 19 May; 7 wk later the first recruits were found on recruit- ment panels at the same dock. Examination of paired samples of encrusting and tendril growth forms collected on 22 July 2010 in Newport, RI, revealed no significant differences in densities of reproductive structures between growth forms. Fifty-nine percent of tagged tendrils in Westport, MA, detached in 2 wk. One hundred percent of tendrils reattached within 48 h to PVC panels in the laboratory, while only 1 in 80 tendrils tethered to bare substrates (rock or concrete) at nearby field sites reattached to the substrate. Tendrils tethered to natural rock were rapidly consumed by preda- tory snails. Further laboratory experiments found a minimum of 8 h of undisturbed contact with the substrate was necessary for D. vexillum tendrils to reattach. Overall, we found that the tendril growth form is an important factor in the population biology of D. vexillum because it increases sur- face area for feeding and reproducing zooids in a space-limited environment.
Highlights
Native to the coastal waters of northern Japan (Stefaniak et al 2012), the colonial ascidian Didemnum vexillum Kott, 2002 has successfully invaded temperate regions of coastal North America, northwestern Europe, and New Zealand (Lambert 2009, Stefaniak et al 2009) over the past 4 decades
To determine the length of time from recruitment to sexual maturity, in July 2011, Didemnum vexillum larvae were settled onto 100 cm2 PVC panels, and gardened to a density of 5 recruits panel−1 to reduce intra-specific spatial competition
These D. vexillum colonies were grown in the field off Bushy Point, Groton, Connecticut suspended in the water column (~2 m off the bottom), isolated from benthic predators, approximately 100 m from the nearest hard substrate that could be a source of competitors’ larvae
Summary
Native to the coastal waters of northern Japan (Stefaniak et al 2012), the colonial ascidian Didemnum vexillum Kott, 2002 has successfully invaded temperate regions of coastal North America, northwestern Europe, and New Zealand (Lambert 2009, Stefaniak et al 2009) over the past 4 decades. D. vexillum readily grows on natural and artificial substrates, including rock (Gittenberger 2007, Osman & Whitlatch 2007), cobble−gravel (Valentine et al 2007b), eelgrass (Carman & Grunden 2010), pilings (Carman & Grunden 2010), and aquaculture gear The presence of D. vexillum can cause serious problems for aquaculture operations (e.g. Auker 2010, Carman et al 2010, Fletcher et al 2013b). These have included the effects of predators and competitors in controlling its abundance and distribution (e.g. Osman & Whitlatch 2007, Carman et al 2009, Dijkstra & Harris 2009, Epelbaum et al 2009, Forrest et al 2013) as well as various life history features of the species (e.g. Valentine et al 2007a, 2009, Auker & Oviatt 2008, Edwards & Stachowicz 2010, Fletcher & Forrest 2011, Fletcher et al 2013a,b)
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