Coastal structures: mapping their distribution and determining their impact on the marine ecosystem Conference Paper
- Author
- Hancock, N.; MacDiarmid, A.; Sturman, J.
- Year
- 2009
- Journal / Source
- Coasts and Ports 2009: In a Dynamic Environment
- Pages
- 7
- Summary
- Artificial coastal structures such as jetties and sea walls can cause changes to the physical marine environment in many ways including providing new hard substra te for colonisation, shading, altering hydrodynamic processes and modifying nearby soft sediment grainsize. Many studies have also shown that artificial coastal structures have modified the surrounding marine ecological community causing changes in species distribution and abundance. But interactions between different types of structures, associated changes in physical processes and the resulting marine ecological patterns are complex and are generally poorly understood. Mapping the spatial distribution of different types of coastal structures categorised according to their physical characteristics is a first step towards understanding and predicting the effects structures are having on the marine environment. As part of the Oceans 20/20 Coastal Survey, the distribution of artificial coastal structures from Spirits Bay to Bream head (on the north-eastern coast of the North Island of New Zealand) were mapped and described. A database was constructed using information from >1400 Northland Regional Council consents and a new classification system was developed that categorises structures based on their physical attributes (size, permeability, materials, angle, orientation, depth and shading). The study area was divided into zones and the distribution of each category among zones was described. The Bay of Islands was clearly the most developed zone in the study region. It had many more structures than any other zone, was the only zone with all categories represented and had the greatest number of each category of structure, sometimes by an order of magnitude. This is likely due to the regions’ resident population and its popularity as a holiday and tourist destination with its well developed local economy. Open coast zones without sheltered areas had the least number of structures and categories. The most common, and widespread, category was ‘other’, 85% of which are ‘unidentified’, generally because they are non-consented. Structure distribution appears to be linked to population and economic drivers as well as the physical geography of the coastline. More information is being gathered by Northland Regional Council on coastal structures and it would be beneficial to maintain and update the database developed during this study. Further research including surveys and field experiments as well as qualitative and quantitative modelling would give a better understanding of how structures interact with physical processes to affect marine ecosystems. Future work would provide guidelines on physical, biological and ecological structure effects to assist with marine coastal operation management decisions, consent applications and policy development. The marine environment would benefit through reduced risk of unplanned, unexpected or unknown changes to the marine ecosystem due to the placement of artificial coastal structures.