Unusual or Extreme Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 299

TABLE 15.2 Upper Temperature Tolerances for Various
Groups of Organisms a

Approximate

Group upper limit ( C)

Fish 38

Vascular plants 45

Insects 50

Ostracods 50

Mosses 50

Protozoa 56

Algae (eukaryotic) 60

Fungi 62

Cyanobacteria 73

Photosynthetic bacteria 73

Extreme thermophilic Bacteria and Archaea 110?

a Reproduced with permission from Brock (1978).

of sulfates. The sulfide is oxidized biologically by sulfur-oxidizing bacteria
(Fig. 13.1) or abiologically, with both processes leading to formation of
sulfuric acid. At the highest temperatures, bacteria that oxidize sulfide are
the dominant primary producers.
In general, the biota of hot springs is less diverse as temperature in-
creases, although some groups such as the cyanobacteria apparently prefer
warm temperatures (30-40°C) (Fig. 15.2). The thermal tolerance limits of
an increasing number of phylogenetic groups are exceeded as temperature
increases above 25°C (Table 15.1). Multicellular plants and animals gen-
erally cannot withstand temperatures greater than 50°C, but some single-

95

Aquatic beetles
Cyanobacteria

71

48

24

0

10 20 30 40 50 60 70 80

Temperature ( … C)

FIGURE 15.2 Number of species of aquatic beetles and cyanobacteria found in springs of
different temperatures (data from Brock, 1978).