Monterey Bay Aquarium Research Institute
Marine Botany

subtidal scene

Stephanocystis 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.




map of North AmericaGlobal
Although the species S. osmundacea seems restricted to the Pacific Ocean, the genus Stephanocystis can be found throughout the world.Stephanocystis is one of two of the most widely distributed fucalean genera across both hemispheres, the other genus being Sargassum.Stephanocystis is found mostly in the Northern Hemisphere, especially in warmer temperate areas like the Mediterranean, Indian, and Pacific Oceans. Some species ofStephanocystis are even found in South Africa.

Stephanocystis osmundacea occurs all along the eastern border of the Pacific Ocean, from Washington in the north to Baja in the south.

Stephanocystis osmundacea needs a hard, rocky substratum, a well-illuminated habitat, and cannot withstand much desiccation. Thus an ideal habitat for this alga would be the sublittoral rocky sea floor, although some specimens can be found in deep rocky tide pools (one such alga lives in a deep rock pool along the shore at Hopkins Marine Station). Several studies have observed the distributions of S. osmundacea in its environment, and the pattern that emerges is that of high abundances ofStephanocystis between four and eight meters depth, with an abrupt drop in abundance past ten meters depth. Plants tend not to be abundant in the shallowest areas. Lower abundances in deep water may be a function of diminishing light, and the absence of Stephanocystis in shallow waters may be a function of severe wave force during those violent winter storms. Although some plants do occur past ten meters, their growth tends to be stunted.

fish with CystoseiraCOMMUNITY
Along the California coast, Stephanocystis osmundacea tends to form mixed surface canopies with the giant kelp: Macrocystis pyrifera. These dense stands of high productivity provide sustenance for many herbivorous invertebrates associated with the kelp forests.

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.

reproductive beads

Many 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 Stephanocystis canopies, drastic losses of habitat diversity resulted, illustrating Stephanocystis's importance in maintaining habitat diversity as a habitat-forming species. Thus,Stephanocystis is a species important to divers and fishermen as well!

Because Stephanocystis's propagules are diploid, they can disperse and develop without worrying too much about a dilution factor, so one might think that recruitment for C. osmundacea would be high. In fact, it seems that Cystoseira actually has very low recruitment, and upon inspecting the conditions required for germination of a diploid propagule, one can easily see why.

C.osmundacea is a lithophyte, meaning that it requires a hard, rocky substratum on which to settle. Monterey BayOne study in Central California noted that S. osmundacea would only settle on bare substratum, while studies at other locations indicate that Stephanocystis 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, Stephanocystis 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 Stephanocystis'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 Stephanocystis.

If a young plant manages to escape becoming a meal, adult Stephanocystis 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 Stephanocystis 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 Stephanocystis's failure to become established in the newly available area following the overgrazing by sea urchins.

Last updated: Mar. 16, 2015