Plastics risk to useful algae
Focus goes on tiny unsung heroes of our marine systems
Broken-down plastics in the ocean are finding their way into our diets — while also harming the marine systems that are crucial for our survival. Nearly 13 million tonnes of plastic waste ended up in the world’s marine environment every year and the volume of microplastics appears to be on the rise.
Environmentalists were recently alarmed to find the problem had reached the pristine waters of Antarctica.
“We are living in an age of plastic,” the University of Auckland’s Dr Julie Hope said.
While research around microplastics had typically focused on fish, shellfish and larger animals in the ocean, less was known about how they affected a group of even tinier organisms.
These were the microalgae that live on the surface of coastal sediments, and which had a disproportionately huge influence. They were responsible for producing sticky sugars that bound seabed sediment together, effectively influencing how it moved about our coasts.
Microalgae also help regulate our climate, capturing CO2 from the atmosphere, and, as a byproduct, producing up to half of the oxygen we breathe.
The carbon they fix from CO2 and nutrients they capture channel up through the food web — from microalgae to larger marine organisms.
Therefore, if the smaller life at the bottom was affected by microplastics, our marine systems might not be as productive or healthy. Vital processes and functions could change, lowering water quality and clarity.
“Microplastics may not only be affecting animals through ingestion but may in fact be affecting the way our whole coastal marine systems function,” she said. “This will ultimately impact our lives as a society as these systems and the functions they carry out are critical for our survival.”
Yet we still know little about what is really happening in this muddy corner of our environment.
“Microalgae are truly the unsung heroes of our marine systems but we are stressing them and the small animals in the sediment from what we do on land. We are increasing the inputs of nutrient and sediment from land use changes — and we are starting to understand the scale at which we are polluting them with microplastics.”
Hope suspected microplastics might even be accumulating in the sticky substances these organisms produced: “If microplastics accumulate where microalgae densities are higher, they may be more likely to be ingested and accumulate up the food web.
“For example, if microplastics are sticking to the microalgae or biofilms on the sediment surface, they will be more likely to be ingested by bivalves and worms that live in the sediment and feed on microalgae.”
These grazers were the primary food source for fish, larger shellfish and birds on our shores, including commercial species we ate.
Microplastics could also carry organic contaminants and release toxins, such as plasticisers and chemicals, to the surrounding environment: “This may affect the ‘health’ of the system or the way it works in many ways such as the primary productivity of the microalgae, the behaviour of animals living in the sediment and a whole suite of processes.”
In a new study, which recently received a $300,000 grant from the Marsden Fund, Hope and colleagues seek to look at these effects in unprecedented detail.
It is expected the study will shed light on the magnitude of this issue for New Zealand.