Despite the high productivity of wetland
plants, relatively little is consumed by
herbivores. Most macrophytes, and particularly emergent species, have tough cell
walls and high lignin content making ingestion difficult. Instead, consumption is
mainly after death, by detritivores; conditioning is important in improving palatabil-
ity of detritus derived from autochthonous wetland plants, just as it is with respect to
allochthonous inputs to other aquatic systems such as rivers and estuaries,
respectively. The high productivity of many wetlands generates large volumes of
detritus, this standing stock being enhanced, in the case of fringing and flood
wetlands, by detritus from external sources washed in from the adjacent water
body; wetland plants act as traps for algae, detached pieces of macrophytes and
detritus originating from the pelagic zone.
Ironically, detritivores often rely upon
macrophytes as structural habitat features,
benefiting from their high surface area. In Tivoli South Bay, a small wetland on the
Hudson River in New York, the detritivorous chironomid Cricetopus sp. accounts for
73% of chironomid larvae in early summer. Although a consumer of fine particulate
detritus, it uses the dominant macrophyte, water chestnut (Trapa natans), as an
attachment structure, reaching densities of 5000 m3 on the underside of its leaves;
numbers of chironomids decline, however, later in the year, possibly as a result of
heavy predation but also because the water chestnut plants become more
emergent, reducing underwater surface area available for colonisation.
