Common name: Dead Man’s Fingers, Sea Sacs
“If Halosaccion is squeezed, seawater jets out through small pores, and otherwise dignified phycologists have been known to use Halosaccion like water pistols in impromptu shoreline water fights.”
-Graham, Graham, Wilcox (2009)
Type locality: Kamchatka Peninsula, Russia
Florideophyceae: Palmariales: Palmariaceae
Halosaccion glandiforme has a distinctive saccate thallus and typically grows in clumps in the lower intertidal (Bulletin, 2013). It ranges from yellow-green with red coloration near the base to completely reddish-brown. The thallus is up to 200 µm thick and is filled with seawater and about a cubic centimeter of gas (Bulletin 2013). When squeezed, water will jet out in a sprinkler-like fashion from multiple microscopic pores throughout the thallus. The thallus reinflates with seawater when next submerged, so don’t feel bad about squeezing it. Thalli are 5 to 15 cm in length and 3 to 4 cm in diameter (Mondragon et al., 2003).
The Pacific coastal distribution of Halosaccion glandiforme stretches from Point Conception, California to Aleutian Islands, Alaska (Mondragon et al., 2003). They are typically found in the mid- to low intertidal and are a common sight on San Juan Island beaches.
The Friday Harbor Laboratories herbarium specimens for this species date as far back as 1904 and include the following collection locations:
Roche Harbor, San Juan Island, WA
Argyle Beach, San Juan Island, WA
Friday Harbor Laboratories, San Juan Island, WA
Minnesota Reef, San Juan Island, WA
Jura Island, San Juan Island, WA
Turn Island, San Juan Island, WA
Turn Point, San Juan Island, WA
Sand Juan Point, Port Renfraw, B.C.
American Camp Beach, San Juan Island, WA
Brown Island, WA
East Sound, San Juan Island, WA
Sucia Island, WA
Box Island, Long Beach, Vancouver Island, B.C.
Botanical Beach, Port Renfrew, B.C.
Hannah Heights, San Juan Island, WA
Wiffin Spit, Vancouver Island, B.C.
Mitchell Bay, San Juan Island, WA
Cape Alara, WA
Kanaka Bay, San Juan Island, WA
Mar Vista, San Juan Island, WA
One voucher specimen was pressed and entered into the FHL herbarium (Fig 2). The recorded collection location and date were FHL Docks and 02 July 2013.
Life history and sexual reproduction
Halosaccion and the remainder of the Florideophyceae exhibit a triphasic life history: a haploid sexual phase (gametophyte), a diploid phase that develops directly on the female thallus (carposporophyte), and a free-living diploid phase that bears meiosporangia (tetrasporphyte). The carposporophyte is retained and nourished by the female gametophyte, a life history aspect that is thought to have evolved in compensation for the lack of flagella in red algal gametes and the resulting inefficiency in fertilization (Cole et al., 1990). To the naked eye, the male gametophyte and the mature tetrasporophyte appear identical. Tetrasporangium on the tetrasporophyte appear as red dots throughout the thallus (Fig. 3a,b).
The streamlined, torpedo-like shape and cyclic inflation and deflation of Halosaccion distichus is unique among algae. In an investigation of the fluid dynamics of its thallus conducted at Friday Harbor Laboratories, Vogel et al. 2013 found that water is lost during emersion via evaporation from the surface and net flow through pores. Water is regained upon submersion due to the elasticity of the thallus and the pressure difference created by water flow along its surfaces, allowing Halosaccion to survive further periods of desiccation. Vogel et al. noted two studies by DePamphilis (1978) and Muenscher (1915) that investigated the direct correlation between desiccation tolerance and water content. The former found that intact Halosaccion were able to survive three hours of sun exposure whereas those whose internal water had been removed were killed much more quickly. The latter found that the exposure time after which the algae could not recover increased with the amount of internal water. Vogel et al. also found that the relatively weak stipe is able to support the algae because of the low drag of the thallus.
Bulletin, B., 2013. Fluid Mechanics of the Thallus of an Intertidal Red Alga , Halosaccion glandiforme Author ( s ): Steven Vogel and Catherine Loudon Published by : Marine Biological Laboratory. , 168(1), pp.161–174.
Cole, K., Sheath, R., 1990. Biology of the Red Algae. New York: Cambridge University Press
Mondragon, J., Mondragon J., 2003. Seaweeds of the Pacific Coast. Monterey: Sea Challengers
Links to additional resources
Diagram of life history and other information: http://depts.washington.edu/fhl/mb/Halosaccion_Emily/lifehistory.html
Page authors and associations
University of Washington