Beds of giant kelp (Macrocystis pyrifera) provide a floating platform for the piscivorous (fish-eating) great egret in the marine waters of California’s Point Lobos State Reserve. What you see from above the water as tangled mats of seaweed are the uppermost fronds of organisms which may reach heights of 60m (read more on Macrocystis pyrifera). In favourable areas, dense, underwater kelp forests form; these support a wide diversity of other organisms. For an excellent summary article on the biology of kelp forest ecosystems, see Steneck, R. et al. 2002. Kelp Forest Ecosystems: Biodiversity, Stability, Resilience and Future. Environmental Conservation. 29:436-459.
Kelps, or the Order Laminariales, are most diverse in the coastal waters of the temperate northeastern Pacific Ocean, with twenty species occurring from Alaska to Baja California.
Botany resource link: Plant for the Planet: A Plant Conservation Checklist for Gardeners (PDF file), a small brochure on gardening with plant conservation in mind from Botanic Gardens Conservation International – Canada.