Induction of metamorphosis of larval echinoids (Strongylocentrotus droebachiensis and echinarachnius parma) by potassium chloride (KCl)

Potassium chloride (KCl) added to filtered seawater induced larval metamorphosis of the regular urchin Strongylocentrotus droebachiensis and the irregular urchin Echinarachnius parma in the absence of any other stimulatory substance, although the sensitivities of these two species differed. Larvae of S. droebachiensis were not affected by concentrations below 80 mM (above normal seawater levels), whereas 10 mM was enough to induce significantly more larvae of E. parma to metamorphose than a filtered seawater control (used to assess spontaneous metamorphosis in the absence of any inductive cue). Relatively high concentrations of KCl (i.e., above 60 mM), which did not appear to adversely affect larvae of S. droebachiensis, were toxic to larvae of E. parma. Presently, some 15 species of marine invertebrates (representing five different phyla) have larvae which are known to react (i.e., settle, attach, or metamorphose) in response to elevated K⁺ (KCl) levels. K⁺ (KCl), which is thought to induce larval metamorphosis via depolarization of externally accessible cells (Baloun and Morse, 1984), appears to be fairly non species-specific as a metamorphic inducer.