The Nexus: an experimental system to study marine larval dispersal

Project Information

Nexus

Grant agreement ID: 700838

DOI 10.3030/700838

Project closed

EC signature date 19 February 2016

Start date 18 February 2017

End date 14 May 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost € 276 107,40

EU contribution € 276 107,40

Coordinated by

THE CHANCELLOR MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Periodic Reporting for period 2 - Nexus (The Nexus: an experimental system to study marine larval dispersal)

Reporting period: 2019-02-18 to 2020-02-17

Summary of the context and overall objectives of the project

The contamination of natural systems with plastic debris has become one of the most pressing global environmental issues. Microplastics (MPs) are of particular concern because their ubiquity and small size make them available for ingestion by a range of aquatic biota. However, despite increasing research efforts, our knowledge about the potential impacts (or lack thereof) of MP exposure on marine organisms remains equivocal. Progress in this field might be hampered in part by the fact that virtually all MP exposure studies restrict their focus to mean-level effects across treatments (e.g. different particle concentrations). The overall goal of this project was the explicit integration of individual-level data into the analysis of behavioural responses to MP contamination. The work was divided into consecutive sub-projects:

1. Potential drivers of inter-individual variation in MP ingestion rates in juvenile fish
2. Individual-level impacts of MP ingestion variation in juvenile fish
3. Effects of MP exposure on in situ survival in settlement-stage fish
4. Multi-level analysis of behavioural responses to MP exposure

The action has resulted in novel insights into MP ecotoxicology by illuminating the impacts of a largely overlooked phenomenon, the difference in MP uptake among individuals.
Overall, our findings call for the incorporation of individual-level data into future MP impact studies, thereby generating a more thorough understanding of this very current threat to marine ecosystems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Overall, this project presents some of the first work to date to assess the effects of individual-level variation on MP impacts. Specifically, we show that phenotypic variation may lead to non-random effects of MP exposure within populations of juvenile fishes and that inter-individual MP ingestion variation may exert strong selective pressures during settlement. Moreover, we show that behavioural responses to MP exposure may go beyond the population level in that exposed hermit crabs exhibited more predictable risk avoidance behaviour than the control. This project highlights the need to incorporate individual-level analyses into MP ecotoxicology research. We hope for broad scientific and popular interest in our findings to help raise awareness of the growing issue of plastic contamination in the world’s oceans.

"Illustrated overview of the MSCA action ""Nexus"""