Rainbow-leaf seaweed (Mazzaella splendens)
The large seaweed blades shown in the middle of the photograph belong to a common intertidal inhabitant of protected rocky shores called the rainbow-leaf seaweed. The blade color is a deep reddish purple. In the field (but just barely seen in the photograph), the surface of the blade has an iridescent sheen or rainbow hue. This is an unusual seaweed characteristic and is a help in identification of the species. The blade's shape can range from oval, as seen here, to narrow, depending on the amount of wave exposure and type of habitat.
Found in the mid- to lower intertidal and upper subtidal of rocky habitats, the plant ranges from southeast Alaska to northern Baja California.
There was an experimental harvest of this seaweed in Washington in the 1970s for its carrageenan content. Carrageenan is used as a smoothing and thickening material in toothpaste, ice cream and paint. There also were large-scale field experiments undertaken by the state Department of Natural Resources in the culture of the species on submerged ropes in south Puget Sound. Both efforts became irrelevant when cheaper sources of carrageenan were found in other countries. However, the experience left the department with expertise in marine plants that has been maintained for 35 years, evolving into a variety of programs including today's activities associated with marine plant inventory, protection and restoration.
David W. Jamison is a marine biologist and Boston Harbor resident.