Investigating food webs from Kaikoura to Golden Bay

In January the University of Otago’s research vessel Polaris II embarked from Dunedin on its latest marine science voyage.

The 6 researchers and two crew on board had a busy itinerary, collecting oceanographic information, water samples, seaweeds, invertebrates and fish from around 25 locations from Kaikoura, Marlborough Sounds, Tasman-Golden Bay and the Cook Strait, before returning to Dunedin.

Dr Steve Wing, Leader of the Ecosystem connectivity project and Prof of Marine Science at the University of Otago, says, “This summer was an excellent start to our field studies in the Cook Strait region. We had a busy itinerary but were able to collect the initial samples needed to understand how marine species are connected to their habitats. We’ve previously studied food webs in Fiordland, the subantarctic islands and Rakiura/Stewart Island, so this work will give an important comparison of what the ‘ecosystem health’ is of these different regions.

This field sampling and research will be repeated for the next two summers, which will show which processes most affect the connectivity of the region’s marine communities, and give a basis for comparison with other marine ecosystems.

Research projects

How has Kaikoura’s food web been affected by the November earthquake?

This project uses forensic chemistry to track nutrients and organic matter from phytoplankton, kelp and eel grass into invertebrates and fish (including commercial species). This will show which species are supported by which habitats, and what their primary sources of organic matter is (ie seaweed, phytoplankton or detritus).

The data will provide insights into:

• Changes that might occur due to disruption of foundation species, eg loss or changes in kelp forest habitats
• How species living in deeper parts of Kaikoura’s submarine canyon are connected to kelp forests or other coastal habitats
• How the ecosystem is connected and what might happen if the food web is changed, eg if top fish species were removed by overfishing

How is salmon farming affecting the food web?

Salmon farming is effectively adding a new source of food – waste organic matter – into the marine food web. This project is investigating which organisms (including blue cod and invertebrates) feed on those waste products of salmon farms, and how they act to mitigate the effects of aquaculture.

The research focuses on tracking chemical signatures of aquaculture waste products, including several important fatty acids associated with salmon food. This gives a ‘fingerprint’ to track where introduced waste organic matter is going, how the food web and ecosystem processes this waste, and how much organic matter is added to the food web relative to fluxes of natural sources.

There is already lots of monitoring associated with salmon farms because of interest in the ecological footprint of aquaculture. Our project builds on this by quantifying the flow of materials into food webs.

This project will provide science to underpin New Zealand’s ‘green tick’ for sustainable aquaculture.

Reef fish communities

Reef fish are a conspicuous and important part of coastal communities. The many species that live along New Zealand’s coasts make their living in different ways, eg a fish community can be made up of predators, omnivores, herbivores and fish that exclusively eat plankton. The community’s makeup is closely linked to how the ecosystem functions. If you remove a predator species the effect on the food web is different than if you remove a herbivore.

This project is quantifying how changes in reef fish communities affect the way the community processes food and nutrients. It will also link changes in species composition and size to how efficiently communities use nutrients and organic matter in key habitat like kelp forests.

This involves quantifying which fish species are present in different habitats, their relative sizes and numbers, and then using forensic chemistry of the food web to link the composition of fish communities to food resources. The data will provide important information on the health and functioning of coastal resources, and how to manage these ecosystems more effectively.

Bivalve communities in estuaries and coastal habitats

This project is linked to the safety of kaimoana/seafood, commercial fishing, and the health of coasts because bivalves provide an extremely important ecosystem service: they filter water of particulates and pollutants, so profoundly affect coastal water quality. For example, a healthy bivalve community can filter the water in an estuary 2–3 times before the tide goes out! They remove bacteria, phytoplankton, detritus and sediment.

This service is so critical that the collapse of bivalve/shellfish communities can be a ‘tipping point’ for estuary ecosystems – without them estuaries can quickly accumulate waste and toxins, and may even become a ‘dead zone’.

Different bivalves perform different functions and filter in different ways – this project will quantify how they feed and filter. The data will provide important information about the ecological consequences of changes to coastal bivalve communities (eg loss of scallop or oyster beds) due to environmental factors or human activity.

• Project proposal

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