This indicator describes the diversity of animals that live in our estuaries. Estuaries are an important part of our coastal marine area. They are productive ecosystems, but are also one of the most sensitive coastal areas, and are at risk from human activities.
Sediment-dwelling animals (such as shellfish, crustaceans and marine worms) are important in estuaries because they cycle nutrients between the sediment and water, stabilise and rework sediments, and are an important food resource for birds, fish, and crabs. Changes in the number of species and/or the number of individual animals may point to impacts from local-scale pressures like pollution, and broad-scale pressures like increased sediment from land use and catchment activities.
Monitoring the sediment-dwelling animals in intertidal sand and mud flats is part of our Regional Estuary Monitoring Programme (REMP). REMP is a State of the Environment monitoring programme. The main objective of the programme is to monitor the health of the region’s estuaries, and sediment-dwelling animals and sediment characteristics are used as indicators of estuarine health. By monitoring a number of sites we aim to build up an overall picture of the state of our region’s estuaries. Long-term monitoring is essential for detecting trends in estuarine health that may be occurring.
We currently monitor the sediment-dwelling animal communities in three estuaries: the southern Firth of Thames, Whaingaroa (Raglan) Harbour, and Tairua Harbour. The animal community characteristics are summarised by a Traits Based Index that makes use of the animals’ biological traits. Biological traits are the physical and behavioural characteristics that define a particular species (e.g. body size, mobility, feeding behaviour).
The Traits Based Index (TBI) tells us about the health of our estuaries. It ranges between zero and one, with one being most healthy and zero being least healthy. We can use the TBI to track the health of our estuary sites over time, and to compare the health of different estuaries.
This indictor shows that most of the monitored sites are moderately healthy and there were only slight changes in the TBI (and therefore in estuarine health) between 2012 and 2015.
This indicator is updated annually.
Coastal Scientist – Science and Strategy.
Updated 19 April 2017