Connections of a River - Connectivity
Vertical: Hyporheic zone
(pg 3 of 7)
The organisms that live in the upper layers of
the hyporheic zone (immediately beneath the stream)
are typical of those found on the streambed
itself-macroinvertebrates such as nymphs of
stoneflies, mayflies, and caddisflies.
Some aquatic insects may spend most of their
life cycle in the hyporheic zone, emerging only to
turn to adults and reproduce. Crayfish, sculpins,
darters, and other fish may sequester themselves in
the gaps in the upper layer of the hyporheic zone
over winter or during floods.
Different organisms live in the deeper reaches
of the zone because of the smaller interstices. No
plants grow here, so there are no true herbivores.
But the hyporheic zone can support detritus feeders
and carnivores, which feed on fine particulate
organic matter and dissolved organic matter. Deeper
still live mostly meiofauna, such as midge larvae.
At the greatest depths, with relatively constant
temperature, low oxygen, and tiny spaces between
particles, are microfauna feeding on the biofilms
that form on sediments.