Alien vs. predator: influence of environmental variability and predation on the survival of ascidian recruits of a native and alien species

Abstract

Drivers of successful introduction of exotic species remain a major headline in marine invasion biology. We ran two experiments aiming to assess factors influencing recruits' survival of one native and one alien ascidian species. A feeding experiment allowed us to monitor microscale variation of generalist fish predation, which varied significantly within a marina. We also monitored the in-situ survival of lab-grown ascidians at three locations within the marina, half with predator cage exclusion. The survival of the native Ciona intestinalis was conjointly highly influenced by location and caging. We were able to identify a link between predation intensity exerted by mobile generalist macropredators and C. intestinalis survival, but none of the measured contaminants accounted for site variability of survival. The non-indigenous Styela clava had significant higher survival and biomass when uncaged, suggesting a positive effect of predation for this species. The natural in situ recruits of C. intestinalis showed higher biomass when caged and may have competed with lab-grown S. clava. Our results suggest that generalist fish predation may play a crucial role in the success of non-indigenous species due to facilitation through competitive release.

Persistent dominance of non-indigenous species in the inner part of a marina highlighted by multi-year photographic monitoring

“…Data from two publications using the same study locations as here was compiled. Pollutants that significantly varied between locations in Gauff et al (2022) for 2019 and all detected pollutants in Kenworthy et al (2018) for 2016 are indicated. Values below the detection limits are indicated for 2016 (with their detection limit).…”

“…The observed differences between these communities might be related to ambient pollution, since pollution levels measured in sediments of the inner location were often higher compared to the entrance (Tab. 1; Kenworthy et al 2018b, Gauff et al 2022). While differences between the entrance and inner communities appeared to be conserved, their differences with respect to the community settled in the middle of the marina were much more variable.…”

“…Consequently, its dominance at the entrance of our marina may explain the observed differences of biodiversity and community structure among locations. This heterogeneous distribution could be caused by various environmental factors such as predation (Schmidt & Warner 1986, Dumont et al 2011, Gauff et al 2022 and copper pollution which is known to negatively affect reproduction and larval development of C. intestinalis (Bellas et al 2001(Bellas et al , 2004 and has been observed at the inner part of the marina (Tab. 1; Kenworthy et al 2018b, Gauff et al 2022.…”

“…This heterogeneous distribution could be caused by various environmental factors such as predation (Schmidt & Warner 1986, Dumont et al 2011, Gauff et al 2022 and copper pollution which is known to negatively affect reproduction and larval development of C. intestinalis (Bellas et al 2001(Bellas et al , 2004 and has been observed at the inner part of the marina (Tab. 1; Kenworthy et al 2018b, Gauff et al 2022. The systematically different community structures at the entrance and the inner of the marina could therefore be also explained by these parameters influencing the presence of C. intestinalis.…”

“…This marina seems to have negligible variability of temperature among locations (< 0.1°C; Gauff et al 2022), but significant variation of several important contaminants with higher contamination at the inner location compared to the entrance (Tab. 1; Kenworthy et al 2018b, Gauff et al 2022. The contaminant levels seem to be relatively stable for the duration of our study (2016 -2019; Tab.…”