Rights: University of Waikato Published 1 March 2018 Download

The Sustainable Seas National Science Challenge is conducting the country’s first national experiment of its kind. Professor Conrad Pilditch explains how scientists are collecting data on the interactive effects of increased turbidity (cloudy water due to sediments) and nutrients on coastal ecosystems.

Why do you think that Conrad refers to marine ecosystems as hidden gardens?


Professor Conrad Pilditch

This is the first national experiment – it’s the largest experiment globally of its kind, actually. We are working across 15 estuaries across Aotearoa, from Northland to Southland. 

We are collecting empirical data and conducting experimental research to investigate tipping points and the consequences of them on New Zealand ecosystems. We are addressing two of the major stressors to our near shore environment. The stressors were identified multiple times during stakeholder workshops, when we asked the community what they thought we should be looking at. Sedimentation, New Zealand is really good at delivering lots of sediments to the coast. 

The other major stressor is an increase in agricultural production – intensification of agriculture –that is delivering nutrients into our near-shore environment as well. Our focus with our empirical studies is understanding the interactions of those two stressors.

We’ve done a lot of work over the years on the sedimentation of estuaries and the impacts it has on the ecosystem function of these systems. We know for example, the hidden garden within these estuaries. These are small plants that exist within the sediments that are microscopic and drive most of the production in our coastal zone. They are the key link to the organisms in the sediment, the shellfish, the worms that the snapper feed on. 

We know when we increase the turbidity in these systems, the lights go out and this hidden garden can no longer be as productive. We know that when the lights go out, this hidden garden isn’t trapping nutrients in the sediment, they come up in the water column and that can fuel macro algal growth and nuisance blooms. With this increasing turbidity, we are seeing big shifts in how these sediments function and that will translate to shifts elsewhere in the ecosystem. 

We also know, as we muddy the water, we begin to affect the biodiversity of those sediments. We alter the numbers of worms, we alter the composition of species that are there and that has implications on how the sediments process nutrients.


The Science Learning Hub acknowledges the contribution of the Sustainable Seas National Science Challenge and Professor Conrad Pilditch.
Footage supplied by the Sustainable Seas National Science Challenge.