Unusual or Extreme Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 309

FIGURE 15.10 Some organisms adapted to utilize the water surface as a habitat. (A) A mos-
quito pupa, Anopheles claviger; (B) a snail, Lymnaea; (C) the cladoceran Scapholeberis mu-
cronata; (D) Notonecta, a water boatman; (E) the water strider, Gerris; (F) Lampropedia
hyalina; (G) the chrysopyte Ochromonas vischerii; (H) the diatom Navicula; (I) Codonosig
botrytis; (J) Botrydiopsis; (K) Arcella; (L) Nautococcus. [reproduced with permission from
(A-E) Guthrie (1989) and (F-L) Ruttner (1963)].

this layer. Bubbles can interact with the chemicals on the surface leading
to production of foams. The foams are stabilized by lipids and other or-
ganic molecules, both natural and human produced.
Organisms that specialize in the surface layer must be able to with-
stand very high levels of light. Such high light must lead to increased en-
ergetic costs associated with repair of cellular damage from free radicals
formed by high-energy UV irradiance. This disadvantage is offset by the
constant influx of nutrients and organic carbon from the air above.
Surface-dwelling organisms can also alter the properties of the habitat.
Surface tension can be manipulated by exuding organic compounds that
spread across the surface. An interesting form of locomotion occurs this
way; the velid, Velia capria, and beetles in the genus Stenus are able to ex-
crete material that lowers the water tension behind them, so the surface
tension in front pulls them forward at speeds up to 70 cm s 1

(Hynes,

1970).