Blue-Green Algae (Cyanobacteria) in Rivers

Abstract

This chapter presents some of the more commonly encountered lotic cyanobacterial taxa. The cyanobacteria are a group of oxygenic prokaryotes present in nearly all aquatic ecosystems. While the ecological importance of this lineage is well known, much confusion exists pertaining to their systematic and taxonomic status. In order to facilitate generic-level identification, we separate the cyanobacteria into four major groupings: the Chroococcales (coccoid cells often in a mucilaginous envelop), the Oscillatoriales (filamentous forms lacking specialized cells), the Nostocales (filamentous with inducible specialized cells), and the Stigonematales (filamentous, obligatory specialized cells coupled with cell division in multiple planes). We discuss the major genera found in each lineage, the current state of the systematics, and the broad ecological roles and niches of these taxa. Dichotomous keys and images are presented to facilitate generic identifications.

Cyanobacterial Terms

Akinete 

Thick-walled spore, often inducible, typically used to survive adverse environments. Frequently employed in species or generic identifications (e.g., Anabaena, Fig. 2.4a). May be apoheterocytic (develop from vegetative cells between heterocytes) or paraheterocytic (develop from vegetative cells outside of heterocytes).

Baeocytes 

Reproductive cells resulting from successive cell division within a mother cell without being liberated and enclosed by a sheath (e.g., Pleurocapsa, Fig. 2.1p).

Calyptra 

A thick covering at the tip of a trichome (e.g., Phormidium, Fig. 2.3c).

Endogloeic 

Growing within mucilage (typically of other algae, e.g., Synechoccocus, Fig. 2.1i).

Exocytes 

Reproductive cells released from apical portions of sessile, heteropolar cells (e.g., Chaemosiphon, Fig. 2.1e).

False branching 

A branch not formed as a result of cell division and does not result in multiple planes, leading to filaments which appear to pass each other (e.g., Tolypothrix, Fig. 2.4e).

Filament 

Linear arrangement of cells enveloped by a sheath (e.g., Phormidium, Fig. 2.3c).

Heterocyte 

A thick-walled cell, often inducible, used to fix atmospheric nitrogen. The size, shape, and placement are frequently employed in identifications (e.g., Anabaena, Fig. 2.4a).

Heteropolar 

Cyanobacterial “body plan” in which basal and apical regions (cells, filaments, trichomes) may be distinguished (e.g., Heteroleibleinia, Fig. 2.3h).

Hormogonia 

A desheathed, reproductive fragment of a trichome typically arising adjacent to necridic cells or heterocytes (e.g., Oscillatoria, Fig. 2.3k).

Isopolar 

Cyanobacterial “body plan” in which each end is identical (e.g., Pseudanabaena, Fig. 2.3b).

Pseudofilaments 

Row of cells incidentally arranged in a linear series, not a single physiological entity (e.g., Stichosiphon, Fig. 2.1k, l).

Pseudovagina 

Sheath for heteropolar cells or pseudofilaments open only at one apical end (e.g., Stichosiphon, Fig. 2.1k, l).

Sheath 

Mucilaginous layer that may surround trichomes or cells. Many varieties exist (e.g., thin, thick, and lamellate) and may be facultative based on environmental conditions (e.g., Microcoleus, Fig. 2.3j).

Trichome 

Filament excluding the sheath (e.g., Arthrospira, Fig. 2.3a).