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Source: NIWA – National Institute of Water and Atmospheric Research

He says invertebrates like worms, crabs and shellfish can provide many of the answers to changes in estuaries.

“We’ve developed indices of estuarine health that are based on the composition of these invertebrate communities. For example, if all the species that are sensitive to mud are disappearing, we might have a strong indication that too much fine sediment is being added to the estuary.

“In a single core of sediment you can get 30 to 40 species and up to 300 individuals.”

“It requires a lot of understanding of these species, but when you know a little about their sensitivities and how they respond to these different types of stressors, you can get good information on what’s happening in the environment and what’s driving it.”

He says the invertebrates that live in estuarine sediments are perfect for this research: they’re long-lived and they don’t move around too much.

As well as studying the invertebrates, researchers also analyse the samples to assess what kinds of sediments and contaminants are entering the estuary.

Lohrer says, together, these methods give researchers a clear understanding of what is changing.

NIWA has worked closely alongside the Auckland Council for more than three decades to monitor estuaries in the region.

Lohrer says that the collaborative nature of the partnership has been key to research success and, ultimately, better estuary management.

“If they trust in the science and can incorporate it into policy that protects the marine environment, for a variety of users and uses, that’s the most beneficial thing.”

“That, to me, is real success.”

After a productive morning on the Mahurangi Estuary, the researchers take a quick look at some of their samples before heading out to the remaining sites.

If carrying the backpacks through the mud was resistance training for the legs, the sieving is a full-on workout for the arms.

After a minute of vigorous shaking, the sediment clears through the mesh, leaving an array of crabs, worms and shellfish.

The researchers funnel the invertebrates into labelled containers filled with an alcohol solution that preserves the samples for laboratory analysis.

Hailes and Carter work like clockwork. It’s almost intuitive for them.