Phenology of Batrachospermum helminthosum (Rhodophyta)

The gametophytes of the freshwater red alga, Batrachospermum helminthosum, are prevalent in temperate regions of North America during the spring. Although this alga is widespread, little is known about environmental factors influencing its growth and reproduction. During spring of 1999, 2005, and 2006, a stream segment with B. helminthosum was monitored for physical and chemical properties along with percent cover of gametophytes. Individual thalli were collected for morphological examination. The highest percent cover was observed in mid to late May and most thalli had disappeared by mid to late June. Spermatangia were abundant in early spring but absent by May. Likewise, immature carpogonia (female reproductive structures) were profuse in early spring and by May only mature carpogonia were observed. The onset of reproduction was accompanied by slowed vegetative growth and a lower number of whorls per plant. The number of carposporophytes (the product of fertilization) increased throughout the spring. Seasonality of growth and reproduction may be more related to light penetration through the canopy than to stream temperature or current velocity. This pattern of growth and reproduction in the spring in B. helminthosum appears to be similar to other freshwater red algae in temperate regions.