Algae

Three species of algae—namely, Enteromorpha procera Ahln., Bangia vermicularis Harv., and Ceramium apiculatum J. Ag., showed on the short-term blocks. E. procera settled in spring (September to November), B. vermicularis appeared in very small numbers in March, 1950, and C. apiculatum in the summer (December–January). The majority of the algal species on the long-term blocks were short lived, more so even than the hydroids—e.g., five species that reached identifiable form appeared on the long-term blocks for one month only. These were Ectocarpus sp. (May), Antithamnion sp. (September), Letterstedtia petiolata J. Ag. (November), E. procera Ahln. (December–January), and Derbesia novae-zelandiae Chapman (April, 1950). Bryopsis plumosa (Huds.) Ag. appeared for two consecutive months. Myriogramme denticulate Kylin and C. apiculatum are the only species with a life span longer than two months under local conditions, appearing on the blocks for three and more months consecutively.

M. denticulata is first recorded as moderately common in July on the long-term block, but does not appear at all on the short-term block, suggesting that the tetraspores take more than a month to reach identifiable size. This species continues to be present in increasing numbers to the end of the experiment. On the last block of the long-term series, this alga, with the sponge Halichondria reticulata, were together the most prominent features of the block. M. denticulata seemed one of the few species that was capable of vigorous growth on a silted surface. At the end of the experiment, some specimens had reached a length of 7·3 cm. C. apiculatum, the other algal species common from July to April, 1950, showed a second set in December and January on the short-term blocks, which probably signifies a life-cycle of about five months. The length of appearance of the species on the long-term block substantiates this.