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Keeping our lagoon water safe for swimming – and for living

Sunday December 15, 2019 Written by Published in Environment
Lab technician Stella Marsters tests the waters from Rarotonga, Aitutaki and Manihiki.  MMR 19121309-19121315 and 19121322 Lab technician Stella Marsters tests the waters from Rarotonga, Aitutaki and Manihiki. MMR 19121309-19121315 and 19121322

From the vibrant warmth of our Cook Islands lagoons, to the clinical chill of the laboratory, a team of scientists work to ensure our waters are safe for tourists, locals, and most of all for the teeming life that calls them home. 


In a cold, dark room marked Chemical Laboratory, Stella Marsters weighs tiny particles that will tell her whether or not the lagoon is safe for plants, animals, and people. 

Marsters, 25, will spend her whole workday here. Wearing a white coat and blue latex gloves, Stella, a technical analyst at the Ministry of Marine Resources, will for hours pour water samples into tubes fitted with filters. 

After she’s transferred all 46 samples, collected from Rarotonga and Aitutaki, she’ll put the filters in the oven, where they will remain overnight to dry.

In the morning, the filters will be moved into a desiccator to remove any remaining droplets of moisture, then put in a furnace to burn off organic, or natural, materials like sand and algae. 

All that will remain on the filters is inorganic material, which might weigh as little as a third of a grain of salt but will give Stella an idea of whether or not the lagoon is clean and safe.

This may not be the work she envisioned when she was studying for a Bachelor’s of Environmental Science at Waikato University. But in a year at the Ministry, she has learnt that science is in the details, and that the details produce larger stories about the world and how we interact with it.

“Usually you only ever learn the things in your given area but for me, and some of our staff in the Ministry, it’s different,” she says. “Although I work as a laboratory technician, I am not limited to learning and understanding how things operate in the lab.” 


The Ministry of Marine Resources began monitoring the quality of water in streams and lagoons in December of 2003. 

A month before the programme’s inception, an airborne irritant had caused more than 700 people in Titikaveka to develop rashes, bleeding noses, and respiratory problems. The source of the sickness was an algal bloom.

Though the alga was natural, there was too much of it; an International Waters Project report published in 2006 attributed the outbreak to mismanaged sewage.

The Ministry of Health responded by issuing warnings and the Ministry of Marine Resources, by designing a programme to test and monitor water around Rarotonga.

The following year, the programme expanded to include Aitutaki, which, like Rarotonga, possessed a tourism industry that put pressure on the lagoon and simultaneously depended on its health. A short time later, Manihiki was added to the programme because its pearl industry was still suffering, three years after bacteria in the water damaged 70 per cent of its oysters.

In the beginning, fisheries officers collected samples, which were analysed in New Zealand at exorbitant cost. Later, with training and support from New Zealand’s National Institute of Water and Atmospheric Research, the Ministry of Marine Resources began processing and analysing its own samples. 

Today, a small team within the Pearl Support & Laboratory Services Division rotates between the lab and the lagoon.

A site in Muri is monitored hourly through a probe attached to a buoy, and a Ministry team collects samples at other sites once a month, sometimes more frequently.

On sampling days, fisheries officers Teina Tuatai and Tutu Turua drive around Rarotonga, stopping at between 20 and 29 sites in the lagoon and at streams, often wading into water up to their waists.

Senior fisheries officer Richard Story visits 17 sites around Aitutaki before dawn so his water samples can make the 9am flight to Rarotonga. 

Ngere George, also a senior fisheries officer, collects six samples from the Manihiki lagoon.

“We go rain or shine, high tide or low tide,” Teina says of sampling days. “Doesn’t matter. We still go.”

At each site, the team records its observations – for example, whether it’s raining or whether there’s digging going on nearby – on a data sheet. One person fills three labelled bottles with water and another uses a handheld machine to take measurements of temperature, salinity, pH levels, turbidity, and dissolved oxygen.

Each of these indicators contributes to a picture of the water’s overall health, just as a series of tests at a physical examination helps a doctor to piece together a diagnosis.

“Every animal has an optimal range that it functions in,” says Dr Lara Ainley, a senior marine ecologist with the Pearl Support and Laboratory Services Division who oversees the water quality monitoring programme.

“For humans, when it gets too hot or cold, we don’t function very well. It’s the same for animals, but in the marine environment it’s not just temperature they have to worry about – it’s all kinds of variables.”

Salinity refers to the water’s saltiness and pH refers to its acidity, which matters because acidic water dissolves coral. Turbidity is a measure of particles in the water; cloudy water can be unpleasant to swim in, but it can also make life and work difficult for marine animals whose job is to filter water.

Dissolved oxygen is the amount of oxygen available for plants and animals, including Manihiki’s pearl-producing oysters, to breathe. When there’s not enough oxygen, such as when an algal bloom suffocates the lagoon, marine life suffers.

“Healthy water is better to swim in,” says Dr Ainley, “but it’s also better to live in.”

In the Microbiology Laboratory, an air-conditioned room lined with shelves of test tubes, Tutu prepares to test this month’s samples for Enterococci and E.Coli – bacteria found in the intestines and passed through waste, which aren’t necessarily harmful but can indicate the presence of viruses and agents that can make people sick.

She lights a gas-powered flame and runs the mouth of each jar containing a sample through it to kill any germs. She then mixes 10 millilitres of every sample with 90 millilitres of distilled water and a culture that will turn a fluorescent colour if it encounters bacteria.

With gloved hands, she pours the mixture into a tray that looks like it’s made for tiny ice cubes, which gets sealed by a machine and placed into an incubator for 24 hours. The heat and humidity will cause any bacteria to grow, and in the morning, Tutu and her team will observe the amount of fluorescent material in the tray.

If bacteria is high in a sample, as often happens after a heavy rain, the team will revisit the site the following day and for several days after that.

Usually subsequent samples show the levels have gone back to normal, which indicates water is moving, but if bacteria levels remain high days later, the site gets flagged as a health concern. Enterococci and E Coli can cause gastrointestinal problems and diarrhea in swimmers.

“We do the testing,” Tutu says. “Our data tells Public Health whether to issue a warning.”

Tutu and her team also measure chlorophyll a, which is essentially food for plants, by adding acetone to samples and freezing them overnight. In the morning, they go into a centrifuge machine, which spins quickly to separate solids from liquids, and then into a spectrophotometer, a machine that measures the amount of chlorophyll a left behind. 

This will offer clues into the lagoon’s primary productivity, or the rate at which plants are performing photosynthesis – in other words, how fast they’re converting energy from the sun into food. The right balance is precarious.

Too much green plant material in the lagoon consumes too much oxygen and blocks the sunlight; too little means there isn’t enough food at the bottom of the chain.

After the team finishes analysing a month’s samples, Teina will email a report to everyone on her list, which includes staff at the National Environment Service, the Ministry of Health, media outlets, and tourism-related businesses.

“The overall water quality score for both lagoon and stream was B, which is good,” the report might begin, and then it will detail the observations and measurements taken at each survey site.

Bacteria, suspended solids, dissolved oxygen, and chlorophyll a get their own grades, between A and F. As per standards published by the World Health Organization, less than 41 bacteria cells per 100 millilitres of water gets an A; more than 500 get an F. Less than one milligram of inorganic solids per litre gets an A and more than 20, an F. More than 95% dissolved oxygen gets an A; less than 40% an F, in keeping with the Australian government’s standards. 

The data offer signposts on the road to adaptive management: close this beach temporarily, it might suggest, or halt development in that area, or tighten regulations for sewage.

“The Ministry of Marine Resources plays a pretty technical role in this process,” explains Dr Ainley. “We provide the data with a lens to respond to and mitigate changes in the quality of our water resources and the ecosystems dependent upon them.”

In other words, the tedious work that Stella does during days in the lab, with only the music coming from her laptop to keep her company, underpins national regulations related to waste, infrastructure, agriculture, development, and health. 

In science, as in life, the decisions are in the details.

·         This article was researched and written with the support of the Ministry of Marine Resources.

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