Experiments testing the use of waste material in estuaries as habitat for subtidal organisms

In addition to producing extensive coastal infrastructure, urbanized estuaries are also often littered with large amounts of waste material. This can be used as habitat by fish and benthic plants and animals. Apart from studies of colonization of artificial reefs, which are usually deployed specifically to enhance populations of fish or to replace degraded habitat, there have been few studies that have specifically examined the use of waste material as habitat. Neither have previous studies compared different types of waste material that one characteristically finds in urbanized estuaries, nor the use of small patches of habitat typically created by waste. Spatial comparisons of species found on previously dumped artificial material may be confounded by the fact that different types of waste may be dumped in different places, or may be of different age. This study built small patch reefs of three different types of widespread waste material (tyres, wood or metal) and compared colonization of these over 19 months to colonization of patch reefs of similar age and size made from natural sandstone. Algal assemblages were similar among the different types of reefs, with all showing more cover and diversity on horizontal surfaces. Invertebrates similarly showed few differences among reefs, although there was greater diversity, primarily due to bryozoans, on the vertical surfaces of wooden reefs. Fish rapidly colonized and used all reefs, with cryptic species showing no differences among types of reefs. Schooling species were, however, more common on all of the waste reefs than on the natural sandstone reefs. Small patches of waste material dumped in estuaries can therefore provide useable habitat for a wide range of estuarine organisms and may form a valuable resource if natural habitats continue to be degraded or lost. Although we are not advocating that rubbish simply be discarded into estuaries with the excuse that it provides habitat, removal of existing rubbish should be considered in terms of multiple changes and disturbances to the environment.