Physiology, ecology, and toxic properties of marine cyanobacteria blooms

Cyanobacteria blooms in marine waters are limited to only a few taxa with Trichodesmium, Richelia, Nodularia, and Aphanizomenon being most commonly observed. Nonheterocystous, nitrogen‐fixing Trichodesmium spp. are found throughout low and mid‐latitude oceans and seas of the Atlantic, Pacific, and Indian Oceans, and this genus is thought to be a major contributor to new nitrogen influx into these nitrogen‐poor systems. Heterocystous, nitrogen‐fixing Richelia and other cyanobacteria form unique symbioses with the centric diatoms, Rhizosolenia and Hemiaulus, in the North Pacific, Caribbean, and North Atlantic. Heterocystous, diazotrophic, toxic Nodularia spumigena is restricted to brackish waters of the Baltic Sea and a coastal estuary of southern Australia and often arises from elevated phosphorus input accompanying anthropogenic activities or vertical mixing processes. The nontoxic nitrogen‐fixing Aphanizomenon flos‐aquae is also common in the Baltic, often co‐occurring with Nodularia in the Baltic and Gulf of Finland but more often found in lower salinity areas of the region. Although each taxon responds to its environment uniquely, it appears that bloom production in the three free‐living cyanobacteria largely supports an active microbial food web through dissolved organic compound flux to heterotrophic bacterial communities and their grazers.