1. Drivers of inter-individual MP ingestion variation in juvenile fish
During different pilot experiments, we repeatedly observed high inter-individual variation in the amount of ingested MP particles among individuals of equal size and age. A literature survey revealed that this inter-individual MP ingestion variation, albeit largely ignored, is a ubiquitous phenomenon in both field and laboratory assessments. The aim of this study was to identify potential phenotypic traits that may drive this variability.
We repeatedly tested behavioural traits (i.e. activity levels) and correlated these with MP ingestion at the individual level. We found moderate but significant relationships of individual phenotype with particle ingestion
2. Individual-level impacts of MP ingestion variation in juvenile fish
The next step was to assess the potential individual-level impacts of phenotype-dependent MP ingestion variation. First, we tested whether MP ingestion variation is consistent within individuals in settlement stage Gilt-head seabream, Sparus aurata. Second, we assessed to what degree this variation may determine individual-level effects of MP exposure on behavioural capacities (i.e. escape response).
Our findings show that consistent inter-individual differences in MP ingestion lead to variable impacts within exposure treatments. Individuals with high MP ingestion rates exhibited significantly reduced escape activity, a result that was masked in sample mean-level analyses. MP ingestion variation may exert strong selective pressures during fish recruitment, as certain individuals may consistently be more exposed than others due to variation in feeding behaviour.
3. Effects of MP pollution on in situ behaviour and survival in settlement-stage reef fish
The above-described findings indicated a reduction in predator avoidance capacities in MP exposed fish. This project aimed at assessing the real impact of MP exposure on predation-related mortality in natural systems.
Larval damselfish, Pomacentrus amboinensis, were caught prior to settlement using light traps and pulse fed microplastic spheres six times over four days. Individuals were then placed in the field on habitat patches made from live coral where their behaviour and survival were assessed by a SCUBA diver.
Exposure to MPs led fish to be bolder, more active and stray further from shelter compared to control fish. Exposed fish accordingly exhibited significantly lowered survival compared to the control group. MP pollution may disrupt population replenishment in coral reef fishes by affecting mortality in a critical life history bottleneck.
4. Multi-level analysis of behavioural responses to MP exposure
In this project we exposed European hermit crabs, Pagurus bernhardus, to different concentrations of MP particles and repeatedly measured behavioural responses at different levels of variation (i.e. population-level, within and between individuals). We observed a decrease of startle response durations – a risk avoidance mechanism – at the population level across MP treatments. Moreover, predictability of this behaviour increased with MP exposure. Overall, MP contamination may render hermit crabs more vulnerable to predation by altering their risk avoidance behaviour.
Dissemination of results:
Different aspects of this MSCA action were presented during oral presentations at two international conferences: (1) International Society for Behavioral Ecology Conference, Aug 2018, Minneapolis, USA; (2) 43rd Annual Larval Fish Conference, May 2019, Mallorca, Spain.
Moreover, the EU funded research has been presented during invited seminars given at different institutions during the in- and outgoing phase.
So far, two peer-reviewed papers have resulted from the funded work, a third one is to be submitted soon:
1. Nanninga, G. B., Scott, A., & Manica, A. (2020a). Microplastic ingestion rates are phenotype-dependent in juvenile anemonefish. Environmental Pollution; doi.org/10.1016/j.envpol.2019.113855
2. Nanninga, G. B., Horswill, C., Lane, S. M., Manica, A., & Briffa, M. (2020b). Microplastic exposure increases predictability of predator avoidance strategies in hermit crabs. Journal of Hazardous Materials Letters; doi.org/10.1016/j.hazl.2020.100005
3. Nanninga, G. B., Kiflawi, M., Holzman, R., & Manica, A. (in preparation) Consistent differential ingestion of microplastics leads to uneven behavioural impacts in juvenile Sea bream.
