Variations in benthic fluxes of sediments near pier pilings and natural rocky reefs.

Marine artificial structures such as pilings are replacing natural habitats, and modifying surrounding areas, often resulting in local decreases in species diversity and facilitation of bioinvasion. Most research on the impacts of artificial structures in marine ecosystems has primarily focused on rocky bottom habitats and biodiversity, overlooking the effects of these structures on the functioning of nearby sedimentary habitats. Here we compared, for the first time, benthic metabolism (O fluxes) and sediment-water nutrient (inorganic nitrogen, phosphate, and dissolved organic nitrogen) fluxes in shallow water sediments adjacent to pilings and natural reefs. We also measured sediment properties (grain size, total organic carbon, total nitrogen, C:N ratio and chlorophyll-a content). We found that sediments near pilings were generally finer with greater C:N ratios than those near reefs, while differences in other sediment properties between types of habitats were dependent on the site. We found significant differences in the oxygen consumption, primary productivity, and net ecosystem metabolism in sediments around pilings compared to sediments near natural reefs, but these patterns differed by site. Net nutrient fluxes were similar in sediments near pilings and reefs at both sites. This study showed that although pilings can be associated with changes in the functioning of sedimentary habitats, patterns and the direction of change seem to vary depending on local conditions.