Monday, July 3, 2017

Life on the Edge

Eastern Amberwing dragonfly hunting the pond edge - Perithemis tenera - REK
While I was fishing in a friend's pond the other day he asked what he should do about the thin layer of scum and algae extending a foot or so out from the dam.  I suggested we take a closer look at it.  I came back the next day with a quart jar and a soup ladle and sampled the area.  (Note to self: wash and return ladle to kitchen drawer - quick!)  I spent the next few hours with an inexpensive video microscope, immersed in the world on the edge.

Like other environments, the energy in the pond's food chain begins with the sun.  Photosynthesis creates the energy that all animals consume, whether directly from the source or as a predator eating the primary consumer.  Autotrophs (think plants and algae) produce carbon based nutrients like glucose from the sun.  Heterotrophs obtain it by "eating" plants, organisms or decaying organic matter.  At the top of the food chain, carnivores like me obtain energy from both plants and herbivorous animals.

Six copepods in a tiny droplet - REK
The algae, cyanobacteria and some protists (all referred to as phytoplankton) are busy out of sight fixing carbon and converting sunlight to sugar.  These are consumed by many tiny creatures like case-carrying worms that drift around in the water, extending out of their cases to feed or to pull their cases along in the water as seen in this video by Linda Bower.*  The microscopic spots floating or flitting around in the water are tiny fresh water crustaceans called copepods, as well as other other zooplankton species that also feed on phytoplankton.

Case-carrying worm and Damselfly nymph - REK
Giant water bug - REK
Next up are the aquatic insects such as the mayfly nymphs which feed on algae, diatoms and detritus, the decomposing plant matter that dies or falls into the water's edge.  These supply food for fish, the reason a fisherman ties a nymph on the flyrod.  It is a bug eat bug world in there, filled with predaceous diving beetles and giant water bugs next up in the food chain.

Salamander larva with duckweed.  Note feathery gills - REK
Hardest to catch in the sample were the salamander larvae, 1/2" long and very athletic.  Based on the dorsal fin that begins in front of the hind legs these could be spotted salamanders that will live on land as adults or newts that live on land as teenagers and then return to the pond as adults.

Our brief look into the "scum" along the pond edge only sampled a few of the many species that depend on the vegetation, detritus and algae in that first 12 inches of shoreline.  Tiny frogs and grasshoppers flitted in and out of the water, patrolling dragonflies watched from the distance and dainty damselflies clung to the grass out of reach.  It is all part of life on the edge of a pond.
I have put together life on the microscope stage in this video including damselfly larvae and snails.
* More sophisticated and fascinating pond video's are in Linda Bower's Youtube Playlist.
7-7-17  Thanks to Rob Hunt, Education Coordinator at DNR for helping to clarify my status as a dedicated heterotroph.