Mangroves are a mud-dwelling plant found in saltmarsh and estuaries. Whangamata’s mangroves have increasingly spread following decades of sedimentation caused by land clearance and development which has created more places for them to grow. Find out more about Whangamata's mangroves and how you can tell us your preferred option for managing them.
About mangroves
Mangroves take root in heavy mud and tolerate being submerged in salt water that would quickly kill other plants. Despite their unforgiving environment, mangrove communities are productive and complex ecosystems. Our only mangrove species (Avicennia marina subsp. Australasica) has been native to New Zealand for thousands of years1, growing along sheltered coastlines and estuaries in the northern part of the North Island and flourishing in warmer areas.
Mangrove communities provide shelter and food for several species of fish and a safe haven for shellfish, insects and rare birds. Mangroves' 'aerial roots' (pneumatophores) provide a place for plants and animals to live among and grow on which in turn provide a food source to other animals in the estuary. In some areas mangroves can protect and stabilise land and form a buffer zone to absorb floodwaters (for example, protecting shore areas from wave action, erosion and flooding). However in other areas (such as streams and other waterways) they can block drainage and contribute to flooding - this is the case in some parts of Whangamata.
Whangamata’s mangroves
Increased mangrove expansion rates in Whangamata Harbour relates to three key points:
- Most of Whangamata’s mangrove expansion has happened during decades of land clearance for urban development, forestry and farming.
- Whangamata's population continues to increase as more people live or holiday in the area. This further increases pressures from land development and other activities.
- The resulting erosion and soil run-off into the area’s waterways has provided a ‘garden’ for the mangroves to expand.
Mangrove expansion is therefore linked to one of the major issues identified in the harbour plan - the effect of sedimentation on the long-term health of the harbour and its catchment. Global warming may also become more important in the future, too, with fewer frosts increasing mangrove seedling survival.
The rapid expansion of mangroves in the Whangamata catchment since 1944 slowed in the late 1990s. Since then mangroves in Whangamata have increased in height but not in area. In fact the area of mangroves has decreased by about four hectares. Further consultation is needed so we can work together to decide how (or if) mangroves should be managed in Whangamata to address their spread. Any decisions will need to be made on a case by case basis, to minimise or avoid any harmful environmental, social, cultural or economic effects in these areas should mangrove management be required.
You can find out more about mangrove expansion and management in the next section below or in our mangrove management options report.
Managing Whangamata’s mangroves
Environment Waikato has identified two key actions to manage mangroves - controlling their spread by removing seedlings and the removal of selected mature mangroves blocking waterways. These actions are managed by Environment Waikato through our resource consent process and navigation safety and river and catchment management activities.
Removing mangroves to achieve other outcomes, like improving views and access to and around the harbour, needs further consultation because the mangrove management issue has remained unresolved throughout the development of the harbour plan.
Before making any decisions on if and how to manage mangroves in Whangamata, there are a number of key points which should be considered.
- The Waikato Regional Coastal Plan recognises the upper Whangamata Harbour as an area of significant conservation value. It also recognises that estuaries around Whangamata Harbour support a wide variety of plant and animal life, including some rare/threatened and/or migratory species.
- Deciding how to manage mangroves will require a trade-off between what the community wants and what's best for the environment.
- If we don't do anything, except continue to remove seedlings, the mangroves will not spread but they will continue to grow. As they grow, they may impact on other habitats, access to and around the harbour may become increasingly difficult and more views could be blocked. On the other hand, clearing large areas of mangroves may create other problems. For example, disturbed sediment may release previously trapped pollutants or shift to create another problem elsewhere. However, there are important gaps in our knowledge of mangroves and their ecological role which means it is extremely difficult to predict what effects may occur and how significant they could be.
- Mangroves can have positive or negative effects on flooding depending on their location. Mangroves in the harbour provide a buffer against waves, protecting the shore from erosion and flooding. However, mangroves in the estuary and river mouths trap sediment and impede water movement. Although this helps maintain water quality the accumulating sediment raises the level of the estuary and river beds, reducing their capacity to store flood waters. In the long-term this increases flood levels and ultimately raises flood risks.
- A number of commercial and residential properties near the Wentworth River and surrounding areas will still be vulnerable to flooding in the future whether mangroves are removed from this area or not. For more information, see the Wentworth River Flood Hazard Assessment Report 20072.
- Managing mangroves is a complex process which is just one part of the harbour plan's overall 'integrated approach'. As a first step, the harbour plan recommends addressing sedimentation by reducing the amount of soil eroding from the land into Whangamata's waterways. This will help limit the places where mangroves can grow. It will also reduce the rate of infilling of the harbour. The harbour plan also recommends further consultation with the community to assist Environment Waikato in making decisions on mangrove management in the future. Consented mangrove seedling removal will also help minimise the further spread of mangroves.
Mangrove seedling removal
Unauthorised removal
In October 2005 and January 2007, unauthorised clearance of mature mangroves and seedlings occurred in the Moanaanuanu Estuary. Unauthorised mature plant removal and seedling removal has also been carried out in other parts of the harbour. Because of the wider issues associated with mangrove clearance (outlined above), it is important that these activities do not continue.3
Environment Waikato is committed to working with all parties to address this issue. Currently, mangrove seedlings only can be removed under the conditions of the current resource consent granted to Whangamata Harbour Care Inc. in December 2006.
Controlled mangrove seedling removal through the resource consent process is an important first step in 'holding the line' and stopping the spread of mangroves until appropriate decisions on the removal of mature mangroves can be reached. The consent process also provides a valuable forum to consider all of the issues outlined above.
Whangamata Harbour Care Inc. consent
In November 2005 Whangamata Harbour Care Inc. lodged a consent application with Environment Waikato seeking to be able to remove mangrove seedlings. The consent was granted in December 2006 by the Environment Court for a 12 year period, with certain conditions to protect bird life, cultural sites and the environment:
- Mangrove seedlings can be removed between January and July.
- Mangrove seedling removal from August to December is not permitted, due to the risk of disturbing bird nesting sites.
- The area of seedling removal covers a significant part of the harbour, but excludes removing seedlings within mature mangrove areas, or in specified cultural or conservation sites.
- Only mangrove seedlings with a single stem can be removed, the removal must be on the seaward side of mature mangrove stands and the removal must be by hand.
Eight hectares – targeted sites
A previous survey of mangrove areas was carried out by Environment Waikato at the community’s request earlier in 2007. This survey identified sites totalling approximately eight hectares as proposed areas for mature mangrove removal based on whether they were:
- contributing to sediment accumulation
- spreading into seagrass habitat
- reducing tidal access to wetlands
- spreading into saltmarsh habitat.
A small number of these areas have had consented clearing carried out and are being carefully monitored to assess any effects from this work. The remaining areas are now under consideration as Scenario 2 in the mangrove management options report.
Six options for managing mangroves
As mentioned above, the harbour plan's findings on sedimentation issues have direct relevance to mangrove expansion. However, there is still disagreement between Whangamata residents, community groups and other organisations on managing mangroves including where and if mangrove removal is required. Environment Waikato is committed to further consultation to address this issue and has developed the Whangamata Mangrove Management Options Report for this purpose.
The options report aims to gather more specific feedback on mangrove management from the Whangamata community and other interested parties. It sets out six 'scenarios' or proposals (including proposed funding/likely costs)4 for managing mangroves in the Whangamata catchment, including 'no removal'.
The scenarios are based on historic mangrove distributions in the harbour in 2002, 1993, 1978, 1965 and 1944 (Scenarios 1, 3, 4, 5 and 6), and a reconsideration of the eight hectares of mangroves outlined above (Scenario 2).
You can download the Whangamata Mangrove Management Options Report in PDF format below and use our feedback form to tell us your preferred option.
For more information on mangroves including a mangrove factsheet and other related publications, see our more information section below.
Funding proposals
Given that the local community would benefit the most from mangrove management, it is proposed that Whangamata ratepayers would pay 80 per cent of the cost of this work through a targeted rate. Because the harbour is a valued place on the peninsula, and is used by others in the district, it is also proposed that the remaining 20 per cent would be paid by other Coromandel ratepayers through the existing Peninsula Project rate.
Download the report and overview
You can view and print the maps by clicking on their names in the table below. 5
Whangamata catchment and key locations maps
Maps of mangrove growth and spread in Whangamata Harbour
Report, overview and map PDFs
You can download the following documents in PDF format below and use our feedback form to give us feedback on them.
Whangamata Mangrove Management Options Report
(1054 kb, 150 seconds to download, 56k modem)
An overview of the harbour and catchment plans and mangrove management options report
(1004 kb, 143 seconds to download, 56k modem)
You can download the full Draft Whangamata Harbour Plan and Draft Whangamata Catchment Management Plan.
If you would like to have a copy of these documents or the feedback form sent out to you, please contact Environment Waikato’s Freephone 0800 800 401.
All of these documents are also available to view at:
- libraries in Thames, Whangamata and Hamilton
- Environment Waikato's offices in Hamilton and Whitianga
- Thames-Coromandel District Council's offices in Thames and Whangamata.
Community feedback
The opportunity to provide feedback closed on Wednesday, 7 November 2007.
More information
Mangroves
You can learn more about mangroves in New Zealand including the pros and cons of their management by downloading free copies of Environment Waikato’s mangroves factsheet. If you prefer, you can order a copy of Environment Waikato’s mangrove factsheet by phoning Environment Waikato's Freephone 0800 800 401. Also see the full harbour plan document, its overview document and the mangrove management options report.
For and against mangrove control
In addition, the National Institute for Water and Atmospheric Research (NIWA) has also produced a publication, ‘For and Against Mangrove Control’. A copy of this publication is available in Appendix II of Environment Waikato’s mangrove management options report or you can download the PDF of the report from NIWA’s website. This publication clarifies the facts about mangroves, the consequences of actions taken in relation to them and the likelihood of achieving goals through these actions. This publication is also available in Appendix II of the "Whangamata Mangrove Management Options report".
Moanaanuanu Estuary Rehabilitation Concept
The Moanaanuanu Estuary is a three hectare area south of the causeway where significant unauthorised clearing of mature mangroves has been carried out. An additional management initiative for this area, the Moanaanuanu Estuary Rehabilitation Concept, 6 has been commissioned by Environment Waikato and is now under consideration by Thames Coromandel District Council.
The concept report contains suggestions and recommendations for a variety of restoration and enhancement work in this area. These are aimed at increasing the recreational and educational opportunities provided and protecting the area’s ecology and creating buffering margins to minimise flooding. Some suggestions include creating or enhancing walkways, boardwalks, bridges and tree lighting; and carrying out weed management and replanting native plants.
Mangroves – other councils
Auckland Regional Council (ARC) and Environment Bay of Plenty (EBoP) have also conducted separate reviews of mangrove issues. EBoP’s review focuses on mangroves management in their region, while ARC’s review focuses on a technical review of the current state of knowledge of mangrove ecology, recent expansion, and its effects.
These reviews are listed below and are available to download free in PDF format from each council’s website. Alternatively, you can contact the councils concerned if you would like a printed copy. Other relevant links on these councils’ websites are also included below:
From Environment Bay of Plenty
From the Auckland Regional Council:
- Full report PDF of ARC’s mangroves review (2007)8 (Technical publication 325: 156 pages) - ‘The New Zealand Mangrove: Review of the Current State of Knowledge’.
- Summary booklet PDF of ARC’s mangroves review (2007), listing the report’s key findings in an easily understandable booklet called 'New Zealand's Mangroves'9 available on ARC’s webpage Mangroves and the Coastal Plan.10
Coastal information
- Environment Waikato has a wide range of information available on coastal issues, monitoring and planning. Environment Waikato’s coastal publications are available to order online, or if you prefer, you can order them by phoning Environment Waikato's Freephone 0800 800 401. Much of this material is available free while other, larger documents or reports can be purchased for a small charge.
- Use our useful links to take you to key areas of Environment Waikato’s website focusing on coasts and coastal hazards. You’ll also find links to information on climate change and coastal weather hazards from New Zealand’s National Institute for Atmospheric and Water Research (NIWA) and the New Zealand Government Climate Change Project as well as links to other councils’ mangroves-related information.
Footnotes
- Pocknall, D.T., Gregory, M.R., and Grieg, D.A. 1989: Palynology of core 80/20 and its implications for understanding Holocene sea level changes in the Firth of Thames, New Zealand. Journal of the Royal Society of New Zealand 19: 171-179.
- Environment Waikato. 2007: Wentworth River Flood Hazard Assessment 2007. Environment Waikato Technical Report 2007/16, Environment Waikato, Hamilton.
- It could be argued that the unauthorised removal of seedlings may have assisted in halting the spread of mangroves in these areas. However, these actions were not carried out under specific consent conditions and monitoring designed to minimise any harmful effects was not done. Therefore it is uncertain how these actions have impacted on plant and animal life in these areas of the estuary.
- Note: costs associated with any potential Environment Court process are not included in the proposed figures provided in the mangrove management options report.
- Note: The ‘eight hectare’ mangrove sites map also shows proposed flood control sites for mangrove management. These sites are managed under Environment Waikato’s River and Catchment Management activities.
- Beca Carter Hollings & Ferner Ltd. 2007: Moanaanuanu Estuary Rehabilitation Concept. 4250648/PFD: T1:65537-SAJ74R01.DOC. Beca Carter Hollings & Ferner Ltd, Tauranga.
- Environment Bay of Plenty, 2007: Estuary Care Review. Report to Council, report no. 010607, May, Catalyst Management Services.
- Morrisey, D., Beard, C., Morrison, M., Craggs, R. and Lowe, M., 2007: The New Zealand Mangrove: Review of the Current State of Knowledge. Auckland Regional Council Technical Publication Number 325, Auckland, New Zealand.
- Auckland Regional Council, 2007: Mangroves in New Zealand. Summary booklet. Auckland Regional Council, Auckland, New Zealand.
- This page also provides a brief overview of ARC’s proposed plan change to the Auckland Regional Plan: Coastal (ARP:C), chapter 16, relating to mangroves.