Coastal biology

Key Points | Report Card | Technical Information | Data

This page contains technical details on how and where we collect this information.

On this page:

• What this indicator is about
  
• Why we monitor coastal biology
  
• Where and how we collect the data
  
• How this indicator is compiled
  
• Guidelines and standards
  
• Limitations
  
• Further indicator developments
  
• When this indicator is updated
  
• More information
  

What this indicator is about

This indicator measures the taxa composition and abundance of benthic macrofauna communities found in estuarine intertidal sand and mud flat habitats in the southern Firth of Thames and Whaingaroa (Raglan) Harbour. It reports on data collected from April 2001 to April 2004. Monitoring the abundance of key taxa of benthic macrofauna will provide the information needed for assessing the state of these two estuaries.

Benthic macrofauna have been widely used as indicators of estuary health and trends in environmental monitoring programmes. They respond predictably to many kinds of natural and human-made stresses. Changes in taxa abundance and composition may indicate changes in the estuary environment.

Benthic macrofauna have many characteristics that make them useful indicators of environmental health:

• They are taxonomically diverse and many taxa are abundant.
  
• They have a wide range of physiological tolerances to stress, feeding modes and life-history strategies, and have the potential to respond to a wide range of environmental changes.
  
• They are relatively sedentary and can’t escape unfavourable conditions, making them good indicators of the conditions in their local environment.
  
• Some taxa are relatively long-lived and can integrate the effects of environmental conditions over longer periods of time.
  
• They are relatively easy to sample quantitatively.
  
• Core sampling in non-vegetated sand and mud flats is less destructive than if similar methods were used in mangroves and seagrass beds.
  
• They are relatively well studied scientifically compared with other smaller sediment dwelling animals, and taxonomic keys are available for most groups.

Why we monitor coastal biology

Estuaries have been identified as being some of the most at-risk coastal ecosystems in the Waikato Region. Effective management of coastal ecosystems needs information about whether the composition and abundance of biological communities are stable, increasing or decreasing over time.

Many of the pressures affecting our region’s estuaries are focused on intertidal sand and mud flats, which occupy significant areas of the estuaries in the Waikato Region. For example, 30 to 50 per cent of the area of eastern Coromandel estuaries consist of sand and mud flats.

Intertidal sand and mud flats are ecologically important, supporting diverse and abundant benthic communities. Benthic macrofauna are important in estuarine ecosystems because they:

• cycle nutrients, organic matter and other material between the sediment and the water column
  
• stabilise estuary sediments - for example, through tube-building
  
• rework estuary sediments - for example, through digging and tunnelling
  
• are an important food resource for birds, fish, shrimp and crabs.

Changes in benthic communities may indicate changes in an estuarine ecosystem, which can result from:

• local-scale pressures – for example, point source pollution
  
• broad-scale pressures – for example, changes in land use and catchment management practices.

Environment Waikato's Regional Estuary Monitoring Programme helps to provide a more comprehensive understanding of the region’s estuarine environments and the threats they face. Monitoring changes in the benthic communities of intertidal estuarine habitats is an aspect of this programme. Environment Waikato uses this information to identify policy responses and make consent decisions so that we can avoid or remedy adverse affects on our estuaries.

Find out about Environment Waikato’s policies relating to natural character, habitat and coastal processes in the section 3 of the Regional Coastal Plan.

Where and how we collect the data

Monitoring sites

We currently monitor benthic macrofauna communities at five sites in the southern Firth of Thames and five sites in Whaingaroa (Raglan) Harbour. Monitoring sites are distributed throughout the main part of each estuary and are located at the mid-intertidal level of non-vegetated sand and mud flats. The sites are representative of the area in which they are located, and have not been selected to be near known or potential sources of human disturbance.

Southern Firth of Thames sites:	Whaingaroa (Raglan) Harbour sites:
Te Puru Gun Club  Kaiaua Miranda  Kuranui Bay.	Te Puna Point Haroto Bay  Ponganui Creek Whatitirinui Island Okete Bay.

Monitoring frequency

Monitoring is undertaken at three monthly intervals in January, April, July and October at:

• Miranda and Kuranui Bay in the southern Firth of Thames
  
• Whatitirinui Island and Okete Bay in Whaingaroa Harbour.

The other sites in each estuary are monitored at six monthly intervals in April and October.

Monitoring history

Monitoring began at the five sites in the southern Firth of Thames and at four of the sites in Whaingaroa Harbour in April 2001 (pilot study). Monitoring began at the fifth site in Whaingaroa Harbour (Ponganui Creek) in October 2001.

Measurement technique

We take twelve cores (13 cm in diameter and 15 cm deep) from a permanent plot located at each monitoring site. Each plot is approximately 10,000 m² (100 m x 100 m), and is divided into 12 equal-sized sectors. Within each sector a random location is selected and a core sample taken. Cores taken in adjacent sectors must be at least five metres apart. Over any six month period cores must be at least five metres from any previous sampling position.

We separate macrofauna from the sediment in each sample using a sieve with 500 µm mesh. We then preserve samples in 70 per cent isopropyl alcohol (diluted with tap water) and stain with Rose Bengal.

In the laboratory we:

1. sort macrofauna from the core samples
   
2. identify macrofauna to the lowest practicable taxonomic level (generally species or species group)
   
3. count the macrofauna
   
4. store the samples in 50 per cent isopropyl alcohol.

Twenty-six indicator species are identified for monitoring:

Non-indicator species are also sorted, classified into major taxonomic groups (amphipods, bivalves, crabs, cumaceans, gastropods, isopods, ostracods, polychaetes, shrimps and ‘other’) and counted.

How this indicator is compiled

This indicator presents benthic community characteristics for each monitoring site in the southern Firth of Thames and Whaingaroa (Raglan) Harbour. The information is derived from the number of each species or species group identified in the core samples collected from each monitoring site from April 2001 to April 2004.

Benthic community attributes include:

• The total and average number of individuals per core sample at each site (N).
  
• The total and average number of taxa per core sample at each site (S). Reductions in the number of taxa may be an indication of environmental stress.
  
• Average number of individuals per core sample in each of the major taxonomic groups (for example, bivalves, gastropods, polychaetes and crustaceans) at each site.

The tables below shows the change in the total number of taxa over time at each monitoring site:

Southern Firth of Thames monitoring sites

Whaingaroa (Raglan) Harbour monitoring sites

As more information becomes available we will analyse changes in indicator species populations and benthic community characteristics over time.

Guidelines and standards

There are no formal guidelines or standards available for assessing this data in New Zealand at present. Our approach is based on similar programmes that have been developed by the National Institute of Water and Atmospheric Research (NIWA). The Auckland Regional Council also uses similar estuary monitoring programmes.

Limitations

It is not possible to identify where a benthic community exists on a continuum of environmental stress, based on the values for any community attribute from a single sampling occasion. It is also not possible to identify what values might be expected for a benthic community at any site if it were not subject to environmental stress.

Differences between benthic communities can be best assessed by:

• comparing different sites along spatial gradients
  
• monitoring individual sites over time.

Currently there is no nationally agreed protocol. We cannot easily compare changes in the benthic communities of Waikato estuaries with those of other regions in New Zealand or overseas.

Further indicator developments

The data presented in this indicator represents a baseline from which future changes in these benthic communities can be measured. Additional monitoring sites in other estuaries will be included in the future.

The Ministry for the Environment has been exploring options for developing national ‘biotic indices’ as measures of estuarine and coastal health, in conjunction with other Central Government agencies. This may influence how this indicator is reported in the future.

When this indicator is updated

This indicator will be updated annually.

More information

Documents available from Environment Waikato

You can order any of these documents from our library. Most documents will incur a charge.

Turner, S. and N. Carter. 2004. Regional Estuary Monitoring Programme: Benthic Macfofauna Communities april 2001 to April 2002 Southern Firth of Thames and Whaingaroa (Raglan) Harbour. Environment Waikato Document #916260.

Turner, S. 2001: Monitoring the Region’s Estuaries – Intertidal Sand-Flat Benthic Communities. Environment Waikato Internal Series 2000/11.

Turner, S. 2000. Proposed Coastal Ecological Monitoring Programme for Environment Waikato. Environment Waikato Internal Series 2000/08.

Useful links

• Environment Waikato – Our Coasts
  
• Ministry for the Environment – New Zealand’s marine environment
  
• New Zealand Oceans Policy
  
• The United States Environment Protection Agency – National Estuary Program

Contact person

Coastal Ecologist – Resource Information Group, Environment Waikato

Quality control procedures

Qualified and experienced personnel carry out all sorting and taxonomic identification. On each sampling occasion a different person resorts, re-identifies and re-counts at least 10 percent of the samples from each site for quality control. The minimum acceptable sorting efficiency is 95 percent, and the minimum acceptable identification and counting efficiency is 90 percent.

Related indicators

• Extent of coastal habitats
  
• Land Use