Effect of substrate deployment timing and reproductive strategy on patterns in invasiveness of the colonial ascidian Didemnum vexillum

• Published in: Marine environmental research Vol. 141; pp. 109 - 118
• Main Authors: Fletcher, Lauren M., Atalah, Javier, Forrest, Barrie M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-10-2018; Elsevier BV
• Subjects: Animals; Aquatic life; Artificial structures; Availability; Biodiversity; Colonies; Colonisation; Deployment; Didemnum; Dominance; Dynamics; Ecosystems; Fouling organisms; Fragmentation; Fragments; Geographical distribution; Inoculation; Interspecific; Introduced Species; Invasiveness; Lag phase; Marine invertebrates; Non-indigenous species; Population Dynamics; Recruitment; Recruitment (fisheries); Reproduction; Reproductive strategy; Sea squirt; Seasonal variations; Seasonality; Seasons; Sedimentation; Settlement; Substrata; Substrates; Succession; Tunicate; Urochordata - growth & development; Sea squirt; Settlement; Succession; Colonisation; Non-indigenous species; Artificial structures; Fouling organisms; Tunicate; Fragmentation
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2018.08.006

The colonial ascidian Didemnum vexillum is a high-profile marine invader, with a geographically widespread distribution after introductions to several temperate regions. D. vexillum has been the focus of several eradication and control programmes globally and the need for specific biological knowledge that relates to establishment processes, persistence, impacts and potential for spread remains. The present study describes temporal patterns of D. vexillum percent cover on experimental substrates over 1.5-years in relation to seasonality of substratum availability, in conjunction with key physical (i.e. temperature and sedimentation) and biological factors (i.e. interspecific competition) at two sites in New Zealand. Colonies showed large fluctuations in percent cover between the two study sites and with reference to timing of bare substratum availability. Colonies generally exhibited an initial lag phase, with peak levels of D. vexillum cover reached during the second summer or autumn post-deployment. The long-term competitive dominance of colonies founded from the reattachment of fragments, as opposed to ambient larval recruitment alone, was also investigated. Increases in colony size as a result of ambient recruitment alone were initially much slower. However, after 12-months colony cover exceeded that of plates inoculated with fragments, suggesting the benefit of the apparent competitive dominance conferred by fragment inoculation is restricted to the early establishment phase. This information will provide increased understanding of the population dynamics of this species, as well as assist in the implementation of effective management strategies through knowledge of environmental drivers of prolific infestations.
•Higher levels of colony cover after substrate deployment in summer or autumn.•Initial lag in colony growth with peak cover reached during the following summer.•Increases in colony size from ambient recruitment alone initially much slower.•Competitive dominance of fragment inoculation restricted to establishment phase.