How much microplastic is in plankton?
As an extension of DRC staff member Dillys Pouponeau’s project zooplankton samples collected around D’Arros and St Joseph will be analysed for microplastics. Using lab methodologies and flowmeter data, Monik will separate microplastics from plankton samples and quantify their concentrations as pieces / m3. Quantification will be assisted with FTIR analysis. These values will also be compared to dry biomass data of zooplankton present in the samples. Not only will this project inform on the extent of exposure of reef manta rays to microplastic pollution, it will also give insights on their implications to the food source of reef manta rays.
Monik Choppy
Who I am had been a difficult path to navigate for a long time. I was a young girl who loved art, science and wildlife clubs. Then I was a very studious person finishing up her A-Levels, and before I knew it I was living abroad in a country that was not at all like the Seychelles. I found myself missing the breath-taking nature of my home country, and so I came back with a new ignited purpose to study Environmental science at the University of Seychelles. Through the University I got to experience D’Arros’s pristine natural ecosystems, from finding...
A Microplastic Meal: Assessing the presence of microplastics within manta-ray (Mobula. alfredi) feeding grounds of D’Arros and the St Joseph Atoll
The key aim of this project is to quantify microplastic concentrations around areas of D’Arros and the St Joseph atoll in hopes to identify its implications to reef manta rays feeding in the area.
The foraging strategies of reef manta rays contribute to its extensive movements between ecosystems, making it a key nutrient cycler that supports coral reef productivity and ecosystem services. However, The IUCN and CITES list M. alfredi as Vulnerable, with the main cause of population declines being fisheries that target mobuilds for their gill plates. Other causes of mortality include accidental entanglement by FADs, bycatch and boat strikes. With the exponential increase in global plastic production, microplastic ingestion by filter feeders such as M. alfredi is yet another growing concern. Plastic ingestion can lead to digestive tract obstruction, puncture, dietary dilution and starvation. Furthermore, due to the large surface area and hydrophobic nature of microplastics, it can act as a sink for persistent organic pollutants. Bioaccumulation of these toxic substances in long-lived species can negatively alter reproductive fitness. M. alfredi are susceptible to these impacts given their conservative life history strategy. It is therefore essential to have baseline information about microplastic pollution in key areas of reef manta ray aggregation such as D’Arros and St Joseph. This is especially important since that to date, microplastics have never been quantified in the area. The influence of microplastic concentration on zooplankton abundance can also bring to light the implications it may have on feeding reef manta rays and their distribution around D’Arros and St Joseph. This can be used to inform MPA management strategies for more effective conservation outcomes.
D’Arros is a key site where reef manta rays aggregate to feed due to abundant zooplankton and the presence of a cleaning station. Cleaning stations offer beneficial opportunities for reef fish to interact with manta rays and remove parasites from their bodies. Additionally, these stations support social interactions such as mating and courtship between individuals. Although D’Arros and St Joseph are ideal aggregation sites, the Amirantes Group are subjected to marine plastic pollution carried by currents from offshore sources. These plastics gradually break down to form microplastics between 1 micrometer to 5 millimeter. While secondary microplastics form in this way, primary microplastics are originally manufactured in this size range and enter oceans through wastewater systems. The sizes of microplastics are analogous with zooplankton, the foundational component of reef manta ray diets. These filter feeders are thus vulnerable to the negative consequences of microplastic ingestion. Although D’Arros and St Joseph are marine protected areas, management of marine plastic pollution must be integrated into reef manta ray conservation strategies given their exposure and vulnerability to microplastics. This project can act as baseline information and a starting point for future efforts.
This project has three aims; to quantify the average concentrations of microplastics within defined sampling sites, to identify if there is a correlation between microplastic concentration and zooplankton abundance, and to calculate the theoretical microplastic ingestion rate of reef manta rays in the area. These aims will be achieved through the following objectives:
- Processing samples in the laboratory at the University of Seychelles. Processing includes sieving, digesting, filtering and storing the microplastic samples until further analysis.
- Counting microplastics in each sample using FTIR analysis at the University of Western Cape.
- Using microplastic count and flowmeter data to quantify microplastic concentrations for each sample.
- Categorizing each sample into defined sampling sites, and using descriptive statistics to find the mean concentration of microplastics for each sampling sites.
- Using a linear regression model to test for a relationship between zooplankton abundance and microplastic concentration.
- Using the theoretical filtration rate for reef manta rays and microplastic concentration data to calculate the theoretical microplastic ingestion rate.