Microplastics induce changes in mussel traits and behaviors

Chemical leachates from plastics used in fishing, shipping and manufacturing affect habitat-forming abilities of mussels

October 27, 2020
For Immediate Release

Contact: Heidi Swanson, (202) 833-8773 ext. 211, gro.asenull@idieh When microplastics release chemicals in seawater, mussels may react by subduing or ramping up traits and behaviors that influence their ability to form mussel beds, says a paper recently published in the Ecological Society of America’s journal Ecological Applications.

The authors staked out mussel collection sites on the coasts of France and South Africa, and painstakingly counted microplastic particles on the sand when waters receded during low tide. They found high densities of microplastics, reporting as many as 950 microplastic particles per square meter at some sites.

A cluster of small, colorful plastic pellets, broken shards, and small toys on a black leather surface. There is a 1-cent coin at the bottom of the photo for scale.

Plastic debris found in the top centimeter of sand within a 25 cm x 25 cm sampling frame, at a beach on the eastern English Channel (France), with a 1-cent coin for size reference. Photo courtesy of Laurent Seuront.

“These densities may sound high, but unfortunately they are not infrequent,” said Laurent Seuront, the paper’s lead author and an ecologist and oceanographer at the French National Centre for Scientific Research. “I found accumulation zones on some beaches of the eastern English Channel where the microplastic pellets alone can reach over 5000 pellets per meter square.”

A pile of about 60 small, smooth semi-transparent plastic pellets on a black leather surface. To the left of the pellets is a 1-cent coin for scale. The pile of pellets is about four times larger than the surface of the coin.

Raw polypropylene pellets. Photo courtesy of Laurent Seuront.

Microplastic debris accumulates in these areas when ocean currents and rivers deposit raw polypropylene pellets and degraded bits of larger plastic products on shorelines. Fishing, manufacturing and transport are major sources of microplastic contamination in coastal waters.

After bringing the mussels back to the lab and acclimating them to plastic-free conditions, the team exposed the mussels to plastic-laced seawater and observed their responses. Two species of mussels responded with a “resilience” strategy, becoming more active and moving around significantly more in leachate seawater than in control seawater. The other two species, however, took a “resistance” strategy – they began producing more of the grippy filaments, known as byssal threads, that help them hang on to solid surfaces.    

Mussels are ecosystem engineers whose dense, bumpy beds form habitat for other species and essentially become part of the landscape itself. Changes in motility and grip, like those that Seuront and his colleagues observed, could therefore influence other communities and ecosystems in important ways.

Two closed mussels shown up close. There are semi-opague green cylindrical threads emerging from the mussels.

A black mussel (Choromytilus meridionalis). Photo courtesy of Bernadette Hubbart (CC BY-ND 2.0).

The United Nations has proclaimed 2021–2030 as the Decade of Ocean Science for Sustainable Development, rallying ocean stakeholders against the declining health of “our planet’s largest life-support system.” But even as global awareness of pollution and other ocean-related challenges continue to grow, the long-term impacts of emerging hazards on many key marine species and systems remain poorly understood.

While trait-strengthening behaviors can help mussels sustain plastic pollution in the short term, Seuront warns that the energy costs of these types of changes may not be sustainable in the long-term. In ecosystems where pollution-affected species serve a basic structural role, the growing prevalence of microplastic contamination could therefore shake the foundation of the system.

Journal article:
Seuront, Laurent et al. 2020. “Microplastic leachates induce species‐specific trait strengthening in intertidal mussels.” doi.org/10.1002/eap.2222

Laurent Seuront1,2,3, Katy R. Nicastro3,4, Christopher D. McQuaid3, Gerardo I. Zardic3
1Univ. Lille, CNRS, Univ. Littoral Côte d’Opale, Laboratoire d’Océanologie et de Géosciences, Lille, France; 2Department of Marine Resource and Energy, Tokyo University of Marine Science and Technology, Minato-ku, Tokyo, Japan; 3Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa; 4CCMAR–Centro de Ciencias do Mar, CIMAR Laboratório Associado, Universidade do Algarve, Campus de Gambelas, Faro, Portugal

Author contact:
Laurent Seuront (rf.srncnull@tnorues.tnerual)


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