Reproductive Periodicities of Some Benthic Algae in Lower Chesapeake Bay

Abstract

Semi-monthly (monthly in winter) studies of the reproductive cycles of 8 benthic Chlorophyta, 3 Phaeophyta, and 18 Rhodophyta were carried out over a period of three years at three different localities in the lower Chesapeake Bay. Of the 29 species studied, 11 are perennial, 6 occur in three seasons, 7 in two seasons, and 5 in one season only. The appearance and disappearance of these algae are closely related to the changes in temperature of the surface water. The annual surface water temperature gradient is 25.6'C and the surface water salinity gradient is 6.2%,. The phenological records for these algae show that the climax of reproductive activity for most of the taxa studied is in summer and early autumn. During that period all Chloro- phyta produce swarmers, the phaeophyte Punctaria plantaginea has plurilocular reproductive organs, and all Florideophyceae develop either carposporangia or spermatangia, or both. The Phaeophyta Petalonia fascia and Scytosiphon lomentaria, as well as the Rhodophyta Porphyra leucosticta and P. umbilicalis, release their reproductive cells in the spring. Most Florideophyceae pass the winter in the tetrasporophytic stage or as a sporeling. Like most of the Chlorophyta and the 3 Phaeophyta, these species have an annual cycle. In some of the Ceramiales however, i.e. Ceramium rubrum, Grinnellia americana, Poly- siphonia harveyi, and P. nigrescens, gametophytic plants and tetrasporophytic plants are present at the same time in two different periods of the year. These algae seem to be biennial rather than annual.