Report: TR 2011/33
Author: M Graeme (Natural Solutions - Marine & Terrestrial Ecologists Ltd) and H Giles (Waikato Regional Council)
Estuaries are highly significant and sensitive ecosystems and have been identified as one of the coastal ecosystems within the Waikato region most at risk from human activities.
Estuaries provide feeding, spawning and nursery habitats for many fish, shellfish and bird species, thereby supporting diverse biological communities. They also provide a buffer between the land and sea interface, influencing coastal erosion and filtering contaminants from the land before they enter the coastal zone. In addition to their important ecological and biogeochemical role, estuaries are also greatly valued by people who use them for cultural, commercial and recreational activities.
Our estuaries are coming under increasing pressure from population growth and coastal settlement, increased demands for recreational uses (e.g. boating and fishing), development in estuaries (e.g. marine farms and marinas), catchment development (e.g. forestry and agriculture), land clearance and reclamation, excavation and dredging (e.g. for boat ramps and boat channels), introduction of invasive species (e.g. Spartina and saltwater paspalum), and resource extraction (e.g. through fishing), as well as long term climate changes including sea-level rise.
Shellfish are very common in estuaries and along intertidal beaches all around New Zealand. They form a major link between the water column and benthic habitats and are an important food source for many fish and bird species. They are also a popular food source for people.
Shellfish populations are sensitive to habitat changes occurring as a result of human activities, such as sediment accumulation, contaminant enrichment or the development of physical structures. For these reasons assessments of bivalve population trends are often used to underpin ecological health or environmental impact assessments.
Waikato Regional Council has a statutory obligation to protect the region’s natural coastal resources. Because of their cultural and ecological importance, the protection of shellfish beds is a priority. In order to protect shellfish beds, or detect any changes to them arising from human activity, it is essential to know their extent, i.e. to map where they are found, and how large and dense the beds are.
Waikato Regional Council has been mapping shellfish beds and habitats in three estuaries: Tairua Harbour, Wharekawa Harbour and Otahu Estuary.
This report presents the results of the Wharekawa Harbour survey.
Wharekawa Harbour shellfish and benthic habitat mapping (2010) (8 mb)
|1.1||Benthic shellfish and habitat mapping project background||3|
|1.2||Benthic shellfish and habitat mapping project objectives||4|
|3.1||Overview and summary statistics||10|
|3.2.1||Subjective substrate classification||12|
|3.2.2||Sediment grain size||15|
|3.2.3||Comparison of subjective categories and grain size||17|
|3.2.4||Comparison of substrate categories with Redox Potential Discontinuity layer||20|
|3.3.1||Abundance and spatial distribution||22|
|3.3.2||Size class distribution||28|
|3.7||Relationship between bivalve density, sediment properties and vegetation||39|
|3.7.1||Bivalve density at sites with different sediment properties||39|
|3.7.2||Bivalve density at sites with different vegetation cover||43|
|4||Summary and discussion||45|
|4.3||Bivalve abundance and distribution||46|
|4.4||Relationships of bivalve abundance with sediment characteristics and vegetation||47|
|4.5||Evaluation of habitat mapping and suggestions for improvement of methods||48|
|Appendix A: Sampling locations||52|
|Appendix B: Data||53|