Human activity has caused plastics to contaminate marine ecosystems around the world. Plastic materials can remain in the marine environment for decades and break down into smaller pieces such as microplastics (i.e. plastics <5 mm). Contamination by microplastics is of particular concern, as they are of similar sizes to natural prey for many marine organisms. The potential effects of microplastics on tropical marine ecosystems, however, including through ingestion by coral reef fish, are still not well understood.

Plastic collected by Dr Frederieke Kroon and her research group along a 100m transect parallel to the water line on One Tree Coconut Beach, a southeast facing beach on Lizard Island itself. Everything in the photo, except the sheet underneath, was collected from this 100 m transect. Many-many more microplastics (plastics <5mm) were in the collection (but not in the photo) and also seen in the sand but not collected (too many and too difficult). No doubt much more is also buried in the beach sand; they only collected from the surface.

Dr Frederieke Kroon is a Principal Research Scientist at the Australian Institute of Marine Science (AIMS) in Townsville, with a background in coastal and marine ecology. Part of her research focuses on understanding the impacts of microplastics on tropical marine organisms and ecosystems, and on identifying their sources to inform contamination reduction strategies. Her current project at the Australian Museum’s Lizard Island Research Station, funded by the 2020 Plastic Pollution Research Grant, is looking at microplastic contamination in mesozooplankton. The project aims to answer the following two questions:

Do microplastics and mesozooplankton accumulate in slicks on the water surface?

Sea slicks, or ocean films, are naturally occurring areas of aggregation for materials, including larval forms of fishes and other mesozooplankton, as well as microplastics. As a result, larval fishes in these sea slicks may experience a higher exposure to, and higher probability of ingestion of, microplastics. To examine this, Dr Kroon’s team collected water and mesozooplankton samples in and outside slicks around Lizard Island in November and December 2020. Both water samples and fish samples will be analysed at AIMS for the presence of microplastics. the findings will show whether microplastic contamination is indeed higher in slicks, and if so, whether this leads to higher consumption of microplastics by larval fish present in those slicks.

Has microplastic contamination of fish larvae changed over time?

Sea slicks, and other physical processes also deliver late stage fish larvae to the nearshore area where fish settle into adult coral reef habitats. As a result, larval fish may be an important vector for the transfer of microplastics into these habitats. To examine this, Dr Kroon’s team collected juvenile reef fishes using light traps in November and December 2020. Light trapping is a well-established method to collect late stage fish larvae and has been used at Lizard Island since the 1990s. In addition to analysing these fish samples for microplastic contamination, historical samples of the same fish species curated by the Australian Museum will also be examined to document decadal patterns in microplastic contamination and ingestion by larval reef fish.

By answering these two questions, the project hopes to determine the susceptibility of coral reef mesozooplankton to microplastic contamination. Specifically, their results will elucidate the role of physical processes in aggregating mesozooplankton and microplastics into slicks and document the potential transfer of microplastics by juvenile fish onto coral reefs. Combined, this will improve understanding of the potential current and future effects of microplastic contamination on coral reef ecosystems.

This two year project is generously funded by LIRRF through a grant received from the Banyer Family and has enabled Dr Kroon to assess the marine ecosystems and organisms from the area to gain a closer look at the current state of contamination in the area. The importance of gaining this knowledge is to understand how these ecosystems are impacted and to best inform decisions and development of solutions moving forward.  A post on Dr Kroon’s prior work on microplastics and other marine microdebris undertaken in the waters around Lizard Island can be read here.

LIRRF has also supported two other projects researching the effects of plastics pollution, generously funded by the Rossi Family.

The (correct, physically-distanced) research team on site at Lizard Island. L-R: Michaela Miller (AIMS@JCU PhD student), Frederieke Kroon (Project Leader), Marina Santana (AIMS@JCU PhD student), Mark McCormick (Collaborator), Samantha Jaworski (AIMS Research Technician).

Neuston tow used to collect microplastics in surface waters inside a slick during the December field trip. The ripples to the right of the net denote the slick boundary.

The sieve shows the sample collected in a surface slick, with numerous microplastics clearly visible, including white, pink, blue, green, yellow and red particles.

edited by Sophie Barkla with Dr Frederieke Kroon.