Estuaries are among our most sensitive coastal places. Home to a wide range of plants and animals (such as birds, fish and shellfish) they are of enormous environmental and economic importance. Improved catchment management will help to protect our estuaries.
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The Waikato region has about 35 estuaries, making up over half of the region’s 1,150 km of coastal shoreline.
These areas include:
- West Coast harbours - Whaingaroa (Raglan), Aotea and Kawhia, and the mouths of the Mokau, Awakino, Marakopa and Waikato Rivers.
- Coromandel Peninsula east coast harbours - such as Whangamata, Whitianga and Whangapoua.
- Coromandel Peninsula west coast harbours - Manaia, Te Kouma and Coromandel.
- The Firth of Thames.
Estuaries form where rivers and streams flow into the sea. They are partly enclosed by land and contain a mixture of fresh and salt water. Salt water moves in and out of estuaries with each tidal cycle.
Estuaries are naturally good at trapping sediments. Rivers and streams carry sediment from the land into estuaries, forming sand and mud flats. Wave and tidal currents also carry sand into estuaries from the sea.
Why our estuaries are important
The region’s estuaries are important places. There are settlements near all of the major estuaries in our region.
- We use estuaries for swimming, boating, fishing and shellfish gathering (recreational, cultural and commercial).
- They provide locations for marinas and marine farms.
- They are the feeding, spawning and nursery habitats for many fish, shellfish and birds.
Estuaries also provide:
- Water filtration – they act as natural silt traps reducing the amount of sediment and other contaminants reaching coastal waters.
- Receiving areas for floodwaters.
One way of measuring the importance of estuaries is by estimating the value of the ecosystem services they provide, such as food production, recreation and habitat for plants and animals. Preliminary estimates indicate that the total value of ecosystem services provided by the region’s estuaries is about 20 times higher than forests and about 50 times higher than land used for farming or horticulture1.
How we use estuaries and the land around them affects these special places. Find out more about threats to estuaries and the effects of land use in their catchments.
What lives in our estuaries?
Estuaries are not just mudflats – they’re highly productive ecosystems. A range of habitat types are found in and around our estuaries including:
- coastal forests
- saltmarshes
- mangroves
- seagrass beds
- sand and mud flats
- rocky reefs
- shallow open water areas.
It’s important to maintain these habitats for the overall health of the estuary and the plants and animals that live there.
Estuarine plants
Seagrass beds occupy extensive sand and mud flat areas in a number of estuaries in the region. Seagrass beds provide shelter and food for a wide range of coastal and estuarine animals. Seagrass also binds land sediments and acts as a wave break.
Mangroves are trees found in the shallow areas of many of the region’s estuaries. Mangroves provide important and valuable habitat. Over recent decades, mangroves have spread in many estuaries and are considered a nuisance in some areas. Read our mangrove factsheet below to find out more about mangroves.
Mangrove factsheet
(298 kb, 42 seconds to download, 56k modem)
Salt marshes form on the edge of our estuaries in areas where there is little wave action and sediment is deposited. They are regularly covered by seawater. Salt marshes are often nurseries for juvenile fish, and are important breeding and feeding areas for birds. In the Waikato region there are three types of salt marsh communities:
- rush/sedge – mostly dominated by jointed wire rush and sea rush found at the mid-to-high tide level
- saltmarsh ribbonwood – a mix of rush/sedge, salt meadow and saltmarsh ribbonwood found at the high tide level
- salt meadow – areas of flat mat-forming plants such as sea primrose, glasswort and remuremu found above the mid-to-high tide level.
Once a fringe of native plants (such as manuka and flax) helped buffer estuaries from surrounding land uses. Unfortunately, people have removed most of these plants from estuary margins. However, you can still find them in some places, such as the south-western area of Kawhia Harbour where regenerating forest extends to the water’s edge.
Invasive plant species are also found in our estuaries, for example Spartina and Paspalum. Find out more about coastal plant and animal pests.
Check out our Extent of Coastal Habitats indicator to find out more about the vegetation in eight Coromandel estuaries (view map).
Estuarine animals
The large areas of intertidal sand and mud flats in our region’s estuaries provide habitat for many animal communities. These areas are home to marine worms, shellfish and crabs which:
- are an important food sources for many fish and birds
- play an important role in cycling material between the sediments and the water column
- stabilise and rework sediments.
Sand and mud flats are also important habitats for:
- commercial and recreational fish and shellfish species
- migratory wading birds and shorebirds (including internationally important species).
The Firth of Thames is one of New Zealand’s three most important coastal stretches for wading and shore birds and is listed as a wetland of international importance under the Ramsar convention. Find out more about the wading birds in the Firth of Thames.
On our West Coast – the extensive tidal flats of the estuaries and river mouths provide feeding grounds, breeding and roosting sites for a large number of birds and have international significance in providing habitat for migratory wading birds.
See our Coastal Biology indicator for more information.
Environment Waikato supports the Hauraki Gulf Forum Community Shellfish Monitoring Project.
Taking care of our estuaries
Environment Waikato manages and requires the monitoring of resource consents for activities that affect the coastal marine area. We are monitoring the health of our estuaries. See our coastal indicators for more information.
One of the most important ways to look after our estuaries is to use good land management in their catchments. Good land management reduces runoff and leaching of nutrients and minimises erosion. Reduced erosion means less sediment and infilling in our estuaries. Find out more about erosion and steps to help to minimise erosion and its effects on water quality.
Care groups, such as Whaingaroa Harbourcare, focus on riparian management and keeping stock away from waterways to enhance their local estuary.
Find out what you can do to help protect our estuaries.
For policy information on coasts check out the Proposed Coastal Plan and the Regional Policy Statement (section 3.5).
Footnotes
- Patterson, M. and Cole, A. 1998: The Economic Value of Ecosystem Services in the Waikato region. Report prepared for Environment Waikato. Massey University, Palmerston North.