Sanctuary Integrated Monitoring Network
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Species Database

Halosaccion glandiforme - Sea Sacs

Sea Sacs image

Geographic range:

Aleutian Islands, Alaska to Point Conception, California

Key features:

Elongate, pale green sacs filled with water and air.


bay (rocky shore), exposed rocky shore, protected rocky shore

Primary common name:

Sea Sacs

Synonymous name(s):

Ulva glandiformis, Halosaccion americanum

General grouping:

Red seaweed/algae

ITIS code:


Geographic Range

Range Description:

Halosaccion glandiforme can be found from the Aleutian Islands, Alaska to Point Conception, California. It is also found throughout the Bering Sea.

Intertidal Height

Lowest intertidal height:

-0.6006006 meters OR -2 feet

Highest intertidal height:

1.50150150 meters OR 5 feet

Intertidal height notes:

Halosaccion glandiforme occurs from the upper to low intertidal.

Subtidal Depth Range

Minimum depth:

0 meters OR 0 feet

Maximum depth:

0 meters OR 0 feet

Subtidal depth notes:

Not found in the subtidal.


bay (rocky shore), exposed rocky shore, protected rocky shore

Habitat notes:

Halosaccion glandiforme grows on rocks in the intertidal. They are often found in obvious clumps in fissures or clefts in rocks. This species is widespread, occurring in both exposed and sheltered areas.


Relative abundance:

Halosaccion glandiforme is abundant and wide spread.

Species Description

General description:

Halosaccion glandiforme is an annual red alga, division Rhodophyta, in the class Rhodophyceae, order Rhodymeniales, and family Rhodymeniaceae. It is an easily recognized species and is often seen in large clusters in the littoral zone. It tends to form isolated patches in more protected waters and extensive mats intermixed with other species in exposed, outer coast areas. It was previously known under the scientific name Ulva glandiformes. There has been some confusion over whether or not Halosaccion glandiforme and Halosaccion americanum are the same species. Recent studies show these two species as indistinguishable, however, the taxonomy of Halosaccion americanum is still considered uncertain.

Distinctive features:

Halosaccion glandiforme has thalli that consist of one or more erect and elongate hollow sacs that arise from a small discoid holdfast. The hollow portion of the thallus is usually filled with seawater with a small air bubble at the tip. When squeezed, the thallus will squirt fine sprays of water. As plants get older, the tips of the thalli can erode and leave the thalli flat or filled with sand. If the plant is young or living in the shade, the thalli are reddish-purple. However, if the plant is older or growing in full sunlight, the color becomes a pale yellowish-brown, especially at the tips.


Halosaccion glandiforme's thalli can grow to be reach 25 cm in length and three to four cm in diameter. However, typically size is only about five to 15 cm in length and two to three cm in diameter.

Natural History

General natural history:

Halosaccion glandiforme's water and gas filled thalli is designed to survive the rugged intertidal environment. The outer smooth surface of the thalli is dotted with five to 15 tiny pores that are hard to see with the naked eye. The pores admit seawater into the thalli, which are filled to capacity except for the tip which is filled with a small gas bubble. The water helps keep the sac cool and moist during low tide allowing the alga to withstand many hours of exposure. The bubble at the tip is oxygen formed by rapid photosyntheis and serves to hold the sac upright when immersed in water. Another adaptation is the thalli’s superb hydrodynamic shape which creates a very low drag. Thus, even though the stipe of this plant may be weak, it will not break. This algae’s thalli is often used by Gammarid Amphipods which chew a hold near the base then enter the watery interior and take up protective residence.


Limpets and other grazing invertebrates feed on Halosaccion glandiforme. They are edible to humans, though are not often consumed.


Halosaccion glandiforme nourishes itself through photosynthesis, converting the energy of light to the energy of carbohydrate molecules.

Feeding behavior


March - November


Halosaccion glandiforme is an annual plant that appears in early spring and then degenerates after the spores are released in the fall.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Mondragon, J. 2003. Seaweeds of the Pacific Coast: common marine algae from Alaska to Baja California. Sea Challengers, Monterey, CA. 97 p.
O'Clair, R.M. 2000. North Pacific Seaweeds. Plant Press, Auke Bay, Alaska. 162 p.
Waaland, R. 1977. Common Seaweeds of the Pacific Coast. Pacific Search Press, Seattle, Washington. 120 p.