Mathematical model describing the population dynamics of Ciona intestinalis, a biofouling tunicate on mussel farms in Prince Edward Island, Canada

A mathematical model was used to describe the population of the aquatic invasive species, Ciona intestinalis in the presence of cultured mussel production. A differential equation model was developed to represent the key life stages: egg, larva, recruit, juvenile and adult. Stage transition rates were calculated from time spent in a stage and transition probabilities. Because surface availability for the settlement phase is a key determinant of population growth, dead juvenile and dead adult stages were also modelled, together with their drop-off rates. This model incorporated temperature dependencies and an environmental carrying capacity. Model validation was carried out against field data collected from Georgetown Harbour, in 2008. Relative sensitivity indices were calculated to determine the most influential factors in the model. The results indicated that the modelled outputs were broadly in agreement with the observed data. Under baseline conditions the number of C. intestinalis increased from early September to late October, after which they reached a plateau at an abundance of approximately five individuals per cm. Sensitivity analyses revealed that a reduction in spawning interval or the development time of larva accelerated C. intestinalis population growth. In contrast, decreasing either carrying capacity or the percentage drop-off of live juvenile and adult stages resulted in a decline in the population. This research provides the first detailed model describing population dynamics of C. intestinalis in mussel farms and will be valuable in exploring effective treatment strategies for this invasive species.