Macroalgae have not been the subject of serious conservation attention. The conservation of biological diversity in terrestrial environments has become recognised as requiring conservation of habitats in order to preserve diversity. This concept is particularly applicable in the marine environment, where macroalgae are limited to the photic zone, and usually grow attached to hard substratum. Three of the major threats to marine macroalgae biodiversity are habitat alienation, pollution and the introduction of exotic (alien) species.The development of the coastline, particularly related to increased population pressure in coastal areas, leads to construction, for example, of marinas, port facilities and canal estates. Developments result in direct destruction of existing communities and indirect changes in hydrodynamics and sedimentation. They may produce extra habitat in the form of new surfaces for colonisation, but there is unlikely to be a net gain in habitat.Reduced water quality in association with development, and from point source and diffuse pollution, also results in macroalgal loss. Generally these losses do not lead to complete loss of a taxon, but the extent of human population growth in the coastal zone will continue to increase the impact on algal populations and certainly lead to zones of diversity depletion resulting from multiple, chronic pollution events.A third major threat to macroalgal diversity is that of introduced species. The examples of Sargassum muticum in Europe, and Undaria pinnatifida in France, Australia and New Zealand, suggest species introduction can cause replacement of dominant macroalgae by introduced species resulting in shifts in communities and their trophic food webs.