Microplastics, fragments of plastic smaller than five millimeters, have been found in nearly every corner of the ocean, from polar ice to tropical reefs. But what happens when these particles meet the smallest inhabitants of coral ecosystems?

Elsa Girard’s Research on Microplastics in Coral Reef Invertebrates

Elsa Girard, a French-Canadian master’s student in Geobiology and Paleobiology at Ludwig-Maximilians University of Munich (Germany), conducted her thesis research at the Coral Eye Marine Outpost on Bangka Island, in collaboration with the No-Trash Triangle Initiative (NTTI).

Investigating Sponges as Bioindicators

Elsa’s research focuses on coral reef sponges: simple but vital filter-feeding animals that constantly pump water through their bodies to feed and breathe. Her project aimed to determine whether and how microplastics are incorporated into sponge tissues, an important step toward understanding the long-term impacts of plastic pollution on coral reef ecosystems.

“Because sponges filter such large volumes of seawater, they may also trap and accumulate microplastics. By studying them, we can gain valuable insights into how widespread plastic pollution really is at the microscopic level.”

Findings: Microparticles Hidden Within

The study revealed that the sponges collected at the Coral Eye reef accumulated very fine sediment (< 200 μm) on their outer layers and within their skeletons.

A total of 34 different particle types were identified, including fragments of shells, coral particles, and degraded man-made materials such as polystyrene, particulate cotton, titanium dioxide, and blue-pigmented particles.

These pollutants were incorporated by eight marine sponge species, at concentrations ranging from 91 to 612 particles per gram of dry sponge tissue. Considering that a sponge can weigh several hundred grams, the team conservatively estimated that a single sponge could contain up to 10,000 microparticulate pollutants within its body.

These findings demonstrate that sponges have a strong potential to serve as natural biomonitors for microparticulate pollutants such as microplastics and other degraded industrial products.

Methods: From Reef to Microscope

At Coral Eye, Elsa carefully collected non-lethal sponge samples from the house reef, ensuring no harm to the organisms or their environment. The samples were examined under a microscope for preliminary observations, then transported to Munich for further laboratory analysis and microplastic quantification.

This dual approach, combining field ecology and laboratory science, provides a clearer picture of the invisible plastic pollution affecting marine life.

Why It Matters

While much attention is given to large plastic waste floating on the surface, microplastics represent a hidden, persistent threat. Their small size allows them to infiltrate the food web, from plankton to fish, and eventually to humans.

By using sponges as natural samplers, Elsa’s research shows a new, efficient way to monitor microplastic contamination in tropical reef systems, offering hope for better long-term monitoring of ocean health.

“Understanding how microplastics interact with marine organisms is essential. It’s the first step toward evaluating their real ecological impact and toward finding solutions.”

The project was carried out in collaboration with the No-Trash Triangle Initiative (NTTI) the local organization born in Coral Eye that since 2017 is working to reduce marine plastic pollution across North Sulawesi. By partnering with NTTI, Elsa’s research connects academic science with real-world conservation efforts, bridging the gap between understanding plastic pollution and taking action to stop it at its source.

The work conducted at Coral Eye was later published in the journal Environmental Pollution

Elsa B. Girard, Adrian Fuchs, Melanie Kaliwoda, Markus Lasut, Evelyn Ploetz, Wolfgang W. Schmahl, Gert Wörheide,
Sponges as bioindicators for microparticulate pollutants?,
Environmental Pollution, Volume 268, Part A, 2021, 115851, ISSN 0269-7491, https://doi.org/10.1016/j.envpol.2020.115851.

Tiny Plastics, Big Questions

Microplastics, fragments of plastic smaller than five millimeters, have been found in nearly every corner of the ocean, from polar ice to tropical reefs. But what happens when these particles meet the smallest inhabitants of coral ecosystems?

Investigating Sponges as Bioindicators

Findings: Microparticles Hidden Within

The study revealed that the sponges collected at the Coral Eye reef accumulated very fine sediment (< 200 μm) on their outer layers and within their skeletons.

A total of 34 different particle types were identified, including fragments of shells, coral particles, and degraded man-made materials such as polystyrene, particulate cotton, titanium dioxide, and blue-pigmented particles.

These findings demonstrate that sponges have a strong potential to serve as natural biomonitors for microparticulate pollutants such as microplastics and other degraded industrial products.

Methods: From Reef to Microscope

This dual approach, combining field ecology and laboratory science, provides a clearer picture of the invisible plastic pollution affecting marine life.

Why It Matters

While much attention is given to large plastic waste floating on the surface, microplastics represent a hidden, persistent threat. Their small size allows them to infiltrate the food web, from plankton to fish, and eventually to humans.

By using sponges as natural samplers, Elsa’s research shows a new, efficient way to monitor microplastic contamination in tropical reef systems, offering hope for better long-term monitoring of ocean health.

The work conducted at Coral Eye was later published in the journal Environmental Pollution

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