Ecological Observations on the Planktonic Cyanophyte Gleotrichia Echinulata1

Gleotrichia echinulata was planktonic in Green Lake (Seattle, Washington) during summer, making its initial appearance between May and early July and disappearing during September. It apparently spent 8 to 10 months of the year on the bottom where colonies developed from spores deposited by the preceding year’s bloom. The depth of spore deposition may be important in determining the success of spore maturation, and solar radiation may be a primary factor in inducing the annual return of this alga to the plankton. The maximum growth rate in 1886 was about 0.124 colony doublings per day. The vertical distribution of the colonies was controlled primarily by wind‐induced currents. The colonies had no measurable effect on light penetration even at a maximum density of over 400 colonies per liter. Laboratory studies indicated that G. echinulata can fix nitrogen. Only one herbivore in Green Lake, Lindia euchromatica, is known to feed on this species.