The first description of a metamorphic inducing substrate for Aplysia californica was Laurencia pacifica, by Kriegstein, Castellucci and Kandel in the early 70's. The prevailing concepts suggested that the metamorphic inducing relationship between a marine invertebrate and algal species was quite unique and singular. Consequently, it became essential to the successful development of the Aplysia  program that Laurencia pacifica, a seasonal cold-water rhodophyte found on the west coast of the United States, be brought into continuous year-round culture. Numerous attempts to isolate a laboratory strain resulted in minimal quantities of algal production and repeated subculturing failed to produce sustainable cultures of any significance. Laurencia's  cold water prerequisite, fastidious culture requirements and seasonal growth patterns limited its potential for a continuous culture environment.
By 1979, the successful intensification of the larval phases led to the production of large numbers of metamorphically competent larvae. The increasing number of competent animals further emphasized the need for a readily available metamorphic substrate and made possible the evaluation of alternative algae as well as extracts. While in Woods Hole, Ma., trials with five northeast coast rhodophytes demonstrated that the transformation from a planktotrophic larval stage to a benthic macroalgae grazer could not only be accomplished with Laurencia  but with all five of the species. Unlike the seasonal limitations imposed by dependency on Laurencia alone, at least one of these five east coast algal species was available throughout the year. In addition, several species readily developed sustainable non-reproductive cultures providing 30-50g/week of actively growing substrate. The most prolific and consistent for metamorphosis and growth, Agardhiella subulata, strain A1, triggered metamorphosis of A. californica  at >90% and grew in continuous culture without replacement for more than eight years. Please turn to page 2-->