Abstract
Sandy beaches are the dominant feature of most of the world's ice-free coastlines, they are increasingly threatened by coastal squeeze and they are relatively poorly understood. Even though it is clear that management intervention is required for the persistence of beaches, especially on urbanised coastlines, it is not particularly apparent how much their demise as functional systems would impact ecological processes in the coastal zone at regional scales. Here, we take the first step in addressing this issue using a case study conducted in KwaZulu-Natal, South Africa. Following a simple mass-balance approach, we assess the total rate of carbon turnover through various coastal habitats, including sandy beaches, rocky shores, estuaries and mangroves. On a per-unit-area basis, sandy beaches turn carbon over relatively slowly in comparison with the other systems. However, when aggregated over the entire study domain, the importance of the role of sandy beaches in this process at regional levels is emphasised. This is particularly true if photosynthesis is omitted from the calculations to provide an estimate of organic carbon consumed by the systems. The facts that beaches are fuelled by allochthonous production and that they do not aggregate organic matter support the intuitive notion that beaches are filters of coastal waters, with much production exported to adjacent systems. The fact that the spatial dominance of beaches means that they cycle comparatively large amounts of allochthonous carbon confirms that this is likely a very important process at regional scales. These results suggest that coherent and integrated conservation strategies are needed for entire coastlines and those beaches should be treated as important ecological components within these plans.