Botryocladia pseudodichotoma (Farlow, 1889) Kylin, 1931
Link to AlgaeBase: http://www.algaebase.org/search/species/detail/?species_id=4919
Type locality: Santa Cruz, California
Taxonomy: Rhodophyta: Eurhodophytina: Florideophyceae: Rhodmeniophycidae: Rhodymeniales: Rhodymeniaceae: Botryocladia
Identification: Botryocladia pseudodichotoma is a very distinct subtidal alga. A single individual will have many saccate blades that are red and filled with mucilage, often in the shape of a grape. Indivudal blades, or vesicles, can be more than 4 cm in length, though smaller vesicles are more common in the waters around San Juan Island.
Distribution: Botryocladia pseudodichotoma is a subtidal alga, and ranges from San Diego, California to British Columbia, Canada.
Vouchers : The FHL Herbarium has many specimens of B. pseudidochotoma retrieved from dredges in the deep waters (as much as 60 ft deep) around San Juan Island. Herbarium samples include specimens from Mosquito Pass, Hein Bank, and Salmon Bank.
Research Notes: A saccate morphology is useful for many algae that are regularly exposed to the desiccating conditions of the intertidal zone at low tide. During emersion at low tide, the water in the vesicle keeps the thallus hydrated and also acts as a source of carbon that allows the alga to continue photosynthesizing (Oates 1985). However, B. pseudodichotoma is not an intertidal alga and does not necessarily face the same selective pressures to be saccate. More than likely, the grape-shaped vesicles arise as streamlined shapes that minimize the drag forces experienced by the alga from the water currents (Vogel 1994).
Another different feature of B. pseudodichotoma is that its vesicles are filled with mucilage rather than air or water. One possible explanation for why it is not filled with water is that a water-filled vesicle would be neutrally buoyant. If the alga needs to compete against neighboring organisms for light, it must be higher than the surrounding structures. In algae this is primarily done through buoyancy, as seen with the tropical alga Turbinaria ornata (Stewart 2004). An air-filled vesicle would certainly be positively buoyant for a subtidal alga, but the vesicle would also be under extreme pressure at the depths where B. pseudodichotoma grows and would require an extremely thick thallus to prevent bursting (Dromgoole 1981). Therefore, a compromise between air- and water-filled vesicles is a mucilage-filled vesicle. Mucilage can be positively buoyant, allowing the alga to compete for light against other algae, but be structurally stable at depths greater than 40 ft without requiring the alga to invest lots of energy into thickening the thallus. Overall, B. pseudodichotoma is a good example of how different lineages of algae can converge to have similar superficial morphology (i.e. a streamlined saccate shape to reduce drag forces from flow) while having different methods of creating and maintaining that morphology based on their specific needs (i.e. water-filled and mucilage-filled for intertidal or subtidal species, respectively).
Dromgoole, F. I. 1981. Form and function of the pneumatocysts of marine algae. I. Variations in pressure and composition of internal gases. Bot. Marina 24: 257-266.
Oates, B. R. 1985. Photosynthesis and amelioration of desiccation in the intertidal saccate alga Colpomenia peregrina. Mar. Biol. 89: 109-119.
Stewart, H. L. 2004. Hydrodynamic consequences of maintaining an upright posture by different magnitudes of stiffness and buoyancy in the tropical alga Turbinaria ornata. J. Mar. Syst. 49: 157-167.
Vogel, S. 1994. Life in Moving Fluids. Princeton University Press.
Author: Nicholas Burnett is a graduate student in the Department of Integrative Biology at the University of California – Berkeley.