Energy sources for aquatic animals in the Orinoco River floodplain: evidence from stable isotopes

Abstract

Stable carbon and nitrogen isotope ratios in autotrophs, aquatic invertebrates and fishes from the Orinoco River floodplain of Venezuela reveal that microalgae, including both phytoplankton and epiphytic (attached) forms, are predominant energy sources for many aquatic animals, even though aquatic vascular plants are much more abundant. Floating mats of the grass Paspalum repens and the water hyacinth Eichhornia spp. harbor particularly high densities of aquatic animals, but isotopic evidence indicates that few species are dependent on organic carbon originating from these plants. The stable isotopic evidence for the trophic importance of algae contradicts traditional interpretations of food webs in freshwater wetlands, which are generally thought to be based largely on detritus originating from vascular plants.

The role of standing dead Spartina alterniflora and benthic microalgae in salt marsh food webs:considerations based on multiple stable isotope analysis

“…However, the success of this approach is predicated upon the ability to distinguish the food resources so topic ally. In addition, there can be seasonal and biochemical variations in the isotopic signature of plant and animal tissue (DeNiro & Epstein 1978, 1981, Cifuentes et al 1988, Fry & Wainright 1991, Simenstad et al 1993, uncertainty in the isotopic shift between trophic levels (Fry & Sherr 1984, Peterson et al 1986, Peterson & Howarth 1987, difficulty in obtaining an effective separation of microscopic algae from sediment and detrital particles (Schwinghamer et al 1983, Hamilton et al 1992, and decomposition effects on the isotopic signature of detritus (Benner et al 1987).…”

Effects of water velocity on algal carbon isotope ratios: Implications for river food web studies

“…Similar measurements of algal ␦ 13 C from epilithic diatoms could not be obtained from the small tributary streams because it was not possible to adequately separate epilithic algae from heterotrophs and detritus. In the tributary streams, where abundance of terrestrial detritus was greater, herbivore ␦ 13 C values may be less accurate indicators of algal ␦ 13 C. However, the high quality of algal carbon may make algae more important to herbivore diets than suggested by its low abundance relative to detritus (e.g., Mayer and Likens 1987;Hamilton et al 1992;Peterson et al 1993).…”

Potential of submerged macrophytes to support food webs in lowland agricultural streams

“…They also have potential to contribute to food webs both directly in the form of fresh or detrital material (Jacobsen and Sand-Jensen 1994;Kornijow et al 1995) and indirectly as a substrate for periphyton (Warfe and Barmuta 2006;Ferreiro et al 2011). However, river food web studies have often examined the relative importance of either terrestrial or algal inputs as the basis for stream food webs, excluding macrophytes, possibly because early research suggested low dependence of macroinvertebrates on macrophyte carbon (Hamilton et al 1992;Bunn and Boon 1993).…”