Results - data and trends
The Excel spreadsheet below contains the source data to this indicator's graphs and any additional data.
- View the map of the 19 estuaries monitored.
- The data for the estuaries on the East Coast was collected from Waikato Regional Aerial Photographs (WRAPS) taken in 2007 and 2012, and the data from the West Coast estuaries from WRAPS taken in 2012.
The table below shows that vegetated habitats make up a large proportion of the total intertidal area of many of the estuaries and harbours in the Waikato region.
- >50 per cent - Otama, Purangi, Whangapoua, Wharekawa and Whitianga
- 25-50 per cent - Aotea, Coromandel Harbour, Kennedy Bay, Manaia, Otahu, Tairua, Te Kouma, Waikawau, and Whangamata
- <20% - Kawhia, Waikato River Estuary, Whaingaroa (Raglan), and Colville Bay
Table 1. Estuary intertidal area (hectares), estuarine vegetation cover (hectares) and percentage vegetation cover, as of 2012.
|Location||Estuary||Intertidal area||Vegetation cover|
|(ha)||(ha)||(% of intertidal area)|
|West Coast||Aotea Harbour||2433||641||26.4|
|Waikato River Estuary*||116||6||5.2|
|Whaingaroa (Raglan) Harbour||2461||94||3.8|
|East Coast||Colville Bay||161||32||19.9|
|Firth of Thames**||7369||1513||20.5|
|Otama River Mouth||19||17||89.5|
|Te Kouma Harbour||71||22||31.0|
* Estuarine vegetation survey covers the area of the river mouth only.
**Estuarine vegetation survey area covers the southern Firth of Thames only and does not include intertidal areas throughout the entire Firth.
The graph below shows the proportions of intertidal vegetation communities found in each of the 19 estuaries.
The relative extent of seagrass beds varies widely across the estuaries and harbours surveyed in the Waikato region.
- >50 per cent - Aotea, Kawhia, Tairua, and Coromandel Harbour
- 25-50 per cent - Whangamata, Wharekawa, Whangapoua, and Te Kouma
- <20 per cent - Whaingaroa (Raglan), Waikato River Estuary, Manaia, Otama, Otahu, Whitianga, Kennedy Bay, and Colville Bay
- No seagrass beds – Purangi and Waikawau estuaries
The West Coast harbours such as Kawhia and Aotea are very large, so the actual extent of seagrass beds is far greater than that of Tairua and Coromandel harbours, despite having similar percentage cover estimates. For example, the total area of seagrass beds in Aotea Harbour is 584 ha, which is more than twice as much as the combined extent of seagrass beds in Tairua and Coromandel harbours.
Invasive plant species
Invasive exotic plants (for example the cord-grass Spartina and saltwater paspalum) are also found in the intertidal areas of the surveyed estuaries. In some estuaries, invasive exotic species make up a significant proportion of the total vegetated habitat.
- >50 per cent - Waikato River mouth
- 25-50 per cent - Waikawau and Kennedy Bay
- 10-25 per cent - Otahu, Otama, and Wharekawa
- 1-10 per cent - Tairua, Whaingaroa (Raglan), Colville Bay, Whitianga, Purangi, Whangapoua
- <1 per cent - Whangamata, Aotea, Coromandel Harbour, Firth of Thames, Kawhia, Te Kouma, and Manaia
Information from the last 40-50 years shows a number of important changes in different vegetated habitats have occurred in estuaries in the Waikato region:
- Increases in the area of mangroves in many estuaries (for example, Firth of Thames, Whitianga, Manaia, Whangamata, Coromandel Harbour, Otahu, Whaingaroa (Raglan), Tairua and Te Kouma harbours).
- Increases in the area of invasive plant species in many harbours and estuaries (for example, Waikato River mouth, Waikawau, Kennedy Bay, Otahu, Otama, Wharekawa, Tairua and Whaingaroa (Raglan).
- Decreases in the amount of wetland areas around some estuaries (for example, Manaia, Coromandel, Whitianga, Tairua, Wharekawa, Whangamata and Otahu harbours).
- Similar trends have been reported elsewhere in estuaries around New Zealand.
Percentage cover of vegetation communities in intertidal areas for surveyed estuaries, as of 2012