Reproductive ecology of the freshwater red alga Batrachospermum boryanum Sirodot in a temperature headwater stream

Abstract

Spatial distribution and abundance of Batrachospermum boryanum gametophytes within a headwater stream in Rhode Island, USA varied considerably over a period of two yeas due to significant changes in dominant substrata. However, periodicity of these plants was similar each year. Juvenile gametophytes were produced by the aseasonal annual ‘chantransia’ stage most abundantly in September and October. Macroscopic gametophytes appeared in Novemberand attained a peak in development during late winter and spring, correlating with relative light penetration through the surrounding tree canopy. The ratio of female to male plants increased from 1:1 in January 4:1 at the end of the growing season in June during both years. Spermatangia production was continuous throughout the growth period, averaging 26000 mm⁻²; mean carpogonial density was 60 mm⁻². Approximately 500 spermatia were released for each carpogonium present and the mean proportion of fertilized carpogonia was 22%. Carposporophyutes typically became detached and acted as dispersal agents, settling at 0.075cm s⁻¹. Current velocities in the stream varied from 10 to 50 cm s⁻¹ and were calculated to carry the carposporophytes 5–35 m downstream. Monospores released by ‘chantransia’ upright filaments also added to population spread.