Nodularia is a cyanobacteria genus that is usually found in warm, brackish or saline lakes and estuaries. In brackish desert lakes it can form dense blooms. Some species of Nodularia are associated with benthic environments, but the most common toxin-forming species, Nodularia spumigena, is planktonic.
Individual Nodularia spumigena cells are oval, compressed (width > length), and tiny (width = 8-16 μm; for comparison, a strand of spider silk is about 5 μm wide). Under magnification, Nodularia spumigena cells are bright blue-green, and appear granular or mottled due to gas vesicles in the cells. The cells are joined together end-to-end to form long, unbranched filaments that are surrounded by clear, often transparent, sticky mucilage. Individual filaments may be straight or slightly bent, but can also be aggregated into tangled clumps.
In addition to ordinary (vegetative) cells, the filaments may contain pale blue or orange heterocytes (also called heterocysts) and large, granular, thick-walled akinetes. Heterocytes are specialized cells that convert dissolved nitrogen gas into ammonium that can be used for cell growth. Akinetes are resting cells that are resistant to cold temperatures and other unfavorable environmental conditions, and can overwinter in lake sediments.
Nodularia spumigena blooms often form during warm, calm weather in saline or brackish lakes, ponds, and estuaries with relatively high nutrient concentrations (nitrogen or phosphorus) or low nitrogen to phosphorus ratios (N:P<15). Although the genus is usually associated with marine and estuarine environments, Nodularia spumigena blooms are common in some warm desert lakes (e.g., Great Salt Lake, Utah and Pyramid Lake, Nevada).
Because Nodularia spumigena is capable of converting dissolved nitrogen gas ammonium, it can dominate blooms when inorganic nitrogen (ammonium, nitrate, and nitrite) is limiting to other types of algae.
Identifying which cyanobacteria species are producing toxins is more difficult that it sounds. Historically, cyanobacteria taxa were described as "potentially" toxic based on whether they were collected in a toxic bloom. With the advancement of culturing techniques and genetic analysis, toxicity information is becoming more exact. But this is an ongoing process, so the toxicity information on these pages should be considered a work in progress.
Nodularia spumigena cells may produce nodularin (liver toxin) and BMAA (beta-Methylamino-L-alanine; nerve toxin).
Higher water temperatures and light appear to be associated with increased toxin production.
Not all Nodularia spumigena blooms result in the release of toxins.
Nodularia spumigena has no commonly used synonyms.
This guide was prepared by Dr. Robin Matthews, former Director of the Institute for Watershed Studies (http://www.wwu.edu/iws/) and professor emeritus at Western Washington University. In addition to this guide she has also written two ebooks (more on the way) on phytoplankton identification (see the "algae books" link on http://www.wwu.edu/iws/) and an online key to the cyanobacteria (http://www.snoringcat.net/cyanobacteria_key/index.html).