Sea sacs

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. The Sea sacs 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. It can reach a length of 25 cm and 3 to 4 cm in diameter; typical sizes are about 15 cm long by 2 to 3 cm in diameter.

Habitat:

Spotted on rocks with other algae in the intertidal zone at low tide (pics 3 and 4). This annual usually grows in clumps on rock or epiphytically on other algae in the mid to low intertidal of semi-protected to exposed habitats.

Notes:

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 hole near the base then enter the watery interior and take up protective residence.