As New Zealanders, we love our oceans. Coastal and offshore waters are our playgrounds and sustain us spiritually and economically. As a nation, we want this ecological relationship to continue – we want to have healthy ecosystems that provide the goods and services we have always enjoyed. However, competing uses of the marine environment, impacts from surrounding land use and global influences such as climate change mean our coastal ecosystems are under increasing stress.
We’ve made mistakes in the past when it comes to managing marine resources – overharvesting led to the collapse of toheroa and mussel beds in parts of the North Island. We’ve also had impacts from one-off events such as the wreck of Rena in the Bay of Plenty and an industrial spill in South Auckland. There are multiple, everyday activities that also impact on marine environments such as sediment and nutrient run-off from land, and there are natural, unexpected stressors that can have devastating effects, such as the November 2016 Kaikōura earthquake.
These are all examples of stressors that can and have led to ecosystem tipping points.
New Zealand’s coastal ecosystems are the most multivalued, multiused and contested ecosystems in the country.Professor Simon Thrush
Simon leads the Sustainable Seas National Science Challenge’s Tipping points in ecosystem structure, function and services project. The project’s mission is “to show how we can better manage marine resources to allow for many uses without loss of ecosystem functions and benefits”. This research is part of the Challenge’s Dynamics Seas research theme, which focuses on ecology and oceanography.
Scientists have known about tipping points – an abrupt change to an ecosystem, often caused by the cumulative effect of many small changes and stressors – for quite a while. However, understanding the theory of tipping points and predicting or preventing them from happening are very different things. A lot of what we know about tipping points is due to hindsight – from investigating the collapse of an ecosystem after it has happened. Simon and the others in the research team want to move from hindsight to foresight.
This is harder than it sounds. Although New Zealand’s scientists know a lot about our terrestrial and aquatic ecosystems, the interactions within and between the physical, biological and chemical components of these ecosystems are very complex. Sustainable Seas scientist Professor Conrad Pilditch refers to these interactions as hidden infrastructure. For example, coastal aquatic vegetation like kelp provides habitat for the juvenile fish that eventually become food for open ocean fish that we consume. Stressors like sediment run-off from the land or taking too many crayfish affect the kelp forests, which in turn affect other parts of the ecosystem. Additional stresses can build up, and eventually the ecosystem becomes at risk of reaching a tipping point.
Evidence to aid management decisions
Currently, we manage our marine environment using limits defined by a single stressor considered in isolation such as contaminant discharges and fishing quotas. The Tipping points research team is looking for clear evidence of the links between stressors and ecosystem responses. This will help to identify tipping points and potential indicators and in turn help managers establish environmental thresholds and targets that consider all the stressors on an ecosystem.
To get this information, the research team has set up New Zealand’s first marine experiment at a national scale. They are investigating how our estuaries are coping with the combined effects of nutrients and sediments – two of the key stressors identified by stakeholders during community consultation. Intensive agriculture and other land use adds excess nitrogen to aquatic systems. Sediments from soil erosion cloud the water, reduce the amount of sunlight available to aquatic plants and change the biological, chemical and physical interactions that take place on the seafloor.
Scientists are gathering data from 24 sites in 15 estuaries stretching from Northland to Southland. It is the largest experiment of its kind in the world. The results will inform and help Sustainable Seas to develop ecosystem-based management (EBM) for Aotearoa, which will help guide our decisions about how we manage and use our marine environments.
Nature of science
The Challenge is gathering an enormous amount data from all over the country. However, the data is meaningless until it is interpreted. Scientists make sense of the data by analysing, critiquing and then reporting it.
Conrad Pilditch and Simon Thrush discuss tipping points and the health of estuaries in this Our Changing World interview. Read about wedge shells, the key role they play, and how nutrient and sediment runoff can distrupt estuary functions.
This article has been developed using resources from the Sustainable Seas National Science Challenge.