Habitat enhancing marine structures: Creating habitat in urban waters

摘要

Although maritime regions support a large portion of the world’s human population, their value as habitat for otherudspecies is overlooked. Urban structures that are built in the marine environment are not designed or managed for theudhabitat they provide, and are built without considering the communities of marine organisms that could colonizeudthem (Clynick et al., 2008). However, the urban waterfront may be capable of supporting a significant proportion ofudregional aquatic biodiversity (Duffy-Anderson et al., 2003). While urban shorelines will never return to theirudoriginal condition, some scientists think that the habitat quality of urban waterfronts could be significantly improvedudthrough further research and some design modifications, and that many opportunities exist to make theseudmodifications (Russel et al., 1983, Goff, 2008).ududHabitat enhancing marine structures (or HEMS) are a potentially promising approach to address the impact of cities on marine organisms including habitat fragmentation and degradation. HEMS are a type of habitat improvementudproject that are ecologically engineered to improve the habitat quality of urban marine structures such as bulkheadsudand docks for marine organisms. More specifically, HEMS attempt to improve or enhance the physical habitat thatudorganisms depend on for survival in the inter- and sub-tidal waterfronts of densely populated areas. HEMS projects are targeted at areas where human-made structures cannot be significantly altered or removed. While theseudtechniques can be used in suburban or rural areas restoration or removal is preferred in these settings, and HEMS are resorted to only if removal of the human-made structure is not an option.ududRecent research supports the use of HEMS projects. Researchers have examined the communities found on urbanudstructures including docks, bulkheads, and breakwaters. Complete community shifts have been observed where theudnatural shoreline was sandy, silty, or muddy. There is also evidence of declines in community composition,udecosystem functioning, and increases in non-native species abundances in assemblages on urban marine structures.ududResearchers have identified two key differences between these substrates including the slope (seawalls are vertical;udrocky shores contain multiple slopes) and microhabitat availability (seawalls have very little; rocky shores contain many different types). In response, researchers have suggested designing and building seawalls with gentler slopes or a combination of horizontal and vertical surfaces. Researchers have also suggested incorporating microhabitat, including cavities designed to retain water during low tide, crevices, and other analogous features (Chapman, 2003; Moreira et al., 2006) (PDF contains 4 pages)ud