Comparative feeding rates of native and invasive ascidians

Abstract

Ascidians have a recent history of species introductions globally, often with strong ecological impacts. Comparisons of per capita effects of invaders and comparable natives are useful to assess such impacts. Here, we explore ingestion rates (IR) and clearance rates (CR) of Ciona intestinalis and Ciona robusta, co-occurring native and non-native ascidians, respectively, from Brittany, France. IR was positively related to food concentration, with the invader responding more strongly to increasing food concentration. CR also differed by species, with the invader demonstrating higher values. C. robusta exhibited a higher functional response (Type I) than did C. intestinalis (Type II). Relative impact measured using seasonal abundance and IR revealed that C. robusta has a much greater impact than C. intestinalis at all food concentrations tested, though the former has a constrained distribution which limits its regional impact. Nevertheless, when abundant, we expect C. robusta to exert a greater impact on algal foods.

Coupling feeding activity, growth rates and molecular data shows dietetic needs of Ciona robusta (Ascidiacea, Phlebobranchia) in automatic culture plants

“…Similarly, investigations 44 indicated that ingestion rates increased linearly with food concentration in another tunicate (Halocynthia pyriformis). However, other studies 35 did not detect a clear maximum in the feeding rates of tunicates, according to the concentrations of particles. In our case, when cultures were managed at higher doses (ad libitum) residual suspended particles were still present before water changes, demonstrating that individuals never starved.…”

“…Similarly, the diet Shellfish produced sufficient growth and survival rates, especially at higher concentrations, but also led to an increase in nitrates and phosphates that the automatic system hardly controlled during the second half of the experiment. The automatic system performed at its best when feed doses were lower and produced acceptable results, at higher concentrations, in the treatment Compound, evidently promoting lower pollution of water, although most chemical and physical parameters were kept in the range preferred by this species 35 . Particle concentrations tested in this study represent sub-threshold levels for most tunicates, because negative effects of particle additions would be expected at concentration greater than 46 mg l −1 according to previous investigations 44 .…”

“…However, C. robusta is becoming an endangered resource in some areas 33 , due to global and local environmental changes impacting its survival. Despite its abundance and the plethora of scientific investigations on its ecology and molecular biology, our knowledge of its feeding physiology is still incomplete 34,35 , and this limits our possibilities for culturing genetically consistent populations for scientific purposes. In fact, improvements of culture methods for marine invertebrates in closed system are prerequisites for a generalized use of transgenic lines 26 .…”

On the RIP: using Relative Impact Potential to assess the ecological impacts of invasive alien species

“…The comparative functional response approach ( Fig. 1), whereby the impacts of invasive species are compared with analogous native species as eco-evolutionary baselines (Dick et al 2017c), have proved a reliable tool for explaining the ecological effects of existing invasive species and predicting the impacts of new, emerging and indeed potential future invaders under a wealth of different contexts (Dick et al 2014, b, c, Crookes et al 2018, Howard et al 2018, Hoxha et al 2018. Such contexts include dissolved oxygen levels (Laverty et al 2015a), habitat complexity (Wasserman et al 2016), temperature regimes (Zamani et al 2006), water chemistry gradients (Kestrup et al 2011), higher order predators (Barrios-O'Neill et al 2014) and parasites (Laverty et al 2017b).…”

Pushing the switch: functional responses and prey switching by invasive lionfish may mediate their ecological impact

“…Three types of FR have been described. A Type I response is characterised by a lack of handling time, where consumption rate increases linearly as resource density rises (Jeschke et al 2014;Hoxha et al 2018). Hyperbolic Type II responses are characterised by high proportional consumption at low resource densities followed by an asymptote, and are widely regarded as destabilising on resource populations, such as prey species that cannot escape predation when relatively rare (Murdoch and Oaten 1975;Hassell 1978).…”