Chaetoceros furcillatus Bailey in the Canadian Maritimes

Historical records show that Chaetoceros furcillatus occurred sporadically in the Canadian Maritimes, but when abundant it grew in early spring for a few weeks following the decline of Thalassiosira nordenskioeldii and preceded the rise of C. debilis. Spores were present along with the vegetative cells even at early stages of the bloom, but they contributed most of the cell densities at the end of the maximum growth period spores sank out of the photic zone in a few days. Spore frequency correlated negatively to temperature and positively to salinity. Two spore morphotypes were found in our samples; paired, large cells with a fused (double) set of setae, and non-paired, small cells with a single (non-fused) set of setae. Non-paired spores are more frequently found in relatively less saline and somewhat warmer stations. Nevertheless, we interpret these two different spore types as a distinct morphological expression of the same species, perhaps at sub-specific level of a form. A nine year record shows a change in relative abundance of this species in Passamaquoddy Bay since 1991, and in the Outer Quoddy region since 1994. Chaetoceros furcillatus has become a consistent and a more abundant component of the local phytoplankton. Two alternative explanations for this increase are considered. Firstly, that the species demonstrates natural cyclicity of population dynamics. Secondly, it has responded to unidentified changes in the environment that result in increased abundance. We draw attention to the fact that this increase coincides with the growth of fish farming in this region. The mid-1980s marks the beginning of an explosive growth and the early-1990s mark economic commercialization of fish aquaculture industry. We also designate the lectotype of the species as a pair of spores on slide 654 curated at the Farlow Herbarium Bailey Diatom Collection and restore the original epithet for this diatom.