The importance of small-scale habitat structure for maintaining beta diversity

Marine soft sediments are often considered to be vast, homogeneous expanses of mud or sand; however, most exhibit small-scale biogenic structures. Generally such structures result from short-term processes, but mollusk shell debris can last for centuries, providing a settlement surface for plants and animals, which in turn stabilize the debris. This study sampled patches of shell debris and the surrounding sediment at increasing distances from the patches to determine the role of the patches in driving beta biodiversity. Sampling was conducted at three similar sites within I km in a marine reserve in New Zealand. The shell debris significantly affected beta diversity at all sites, although the magnitude of the effect was dependent on patch size, density, and debris particle size. These results have important implications for estimating and mapping biodiversity. They also have implications for marine conservation. The role of shell debris, suggested by this study, in increasing and maintaining biodiversity, emphasizes a need for reducing disturbance regimes and actively managing seafloor habitats in areas not previously considered for such.