Cystoseira is one of the most widely distributed genera of the Fucales order and provides an essential habitat for many epiphytes, invertebrates, fish, and even humans.
The structure of the numerous tall alga and their associated surface canopies provide a unique habitat for many marine organisms. The canopies provide protection from strong irradience for understory algae, including germlings of the larger algae, as well as diminishing water flow. The canopy can serve as a foraging area for many invertebrates, as well as provide protection from predation.
species of fish are associated with these stands of seaweed canopy, either
for their camouflage value, or for the high productivity contributing
to such tasty munchies as invertebrates and herbivorous fishes. In experimental
removals of Cystoseira canopies, drastic losses of habitat diversity
resulted, illustrating Cystoseira's importance in maintaining
habitat diversity as a habitat-forming species. Thus, Cystoseira is
a species important to divers and fishermen as well!
C.osmundacea is a lithophyte, meaning that it requires a hard, rocky substratum on which to settle. One study in Central California noted that C. osmundacea would only settle on bare substratum, while studies at other locations indicate that Cystoseira has higher settlement in areas of algal turf than in areas covered by encrusting corallines or dominated by a full canopy, even of its own species. Thus, Cystsoseira must first be able to find space for itself on suitable substratum. Secondly, this alga prefers a well-illuminated habitat, and may have to compete with larger algae for light within its vicinity. Grazers present perhaps the toughest obstacle to settlement. Even if Cystoseira's embryos can find a well-lit space on suitable substratum, they can easily become a bite-sized snack for a hungry invertebrate. Thus, post-settlement mortality plays a key role in determining the abundance of Cystoseira.
If a young plant manages to escape becoming a meal, adult Cystoseira plants have high survivorship. This coupling of low recruitment with high survivorship seems to indicate a population of slow turnover. This strategy may work over the long term, especially in light of how well Cystoseira seems to weather violent storms. However, another significant physical disturbance may be enough to wipe out local populations this alga, as in the case of a mass mortality induced by sea urchins that occurred on the Central California coast. A study that described the reestablishment of local flora and fauna noted Cystoseira's failure to become established in the newly available area following the overgrazing by sea urchins.