Man-made intertidal habitats are seen as a key way to maintain and improve the ecology of heavily modified estuaries such as the Thames. Development and coastal squeeze in urban centres leads to the loss of existing intertidal habitat; man-made sites can therefore be valuable tools for habitat mitigation and compensation.
The fish that utilise man-made intertidal habitats were the focus of this MSc dissertation. Population size and species diversity was sampled at two nearly identical man-made intertidal habitats on a reach of the River Roding at Barking Creekmouth. Crucially, these sites were of different ages and, using a combination of sampling and historical data, it was possible to see variations over time.
The two sites were seven years and one year old respectively, allowing for an interesting comparison between new and mature sites. Data from a fish population study at the older of the two sites was also used to support this comparison.
It was found that a significant succession takes place within these sites which subsequently has an effect on the fish that are able to use it: The older site was found to have a very dense stand of Phragmites australis that had encroached into the main channel; this appeared to directly impede fish passage and greatly reduced the depth of the habitat. This contrasted with the younger site which was at the beginning of its succession with open water throughout and had no stands of vegetation, thus providing little shelter and low habitat complexity.
It was concluded that the progression of vegetation succession within man-made intertidal habitats is a key determinant of the abundance and diversity of fish utilising it. It follows, therefore, that this succession determines the success of such a site in providing good habitat for fish. The report suggested important considerations for the planning of future man-made intertidal habitats so that fish can continue to benefit from them sustainably and the benefits of the habitats are not lost over time.
