The Biology of Periphyton

You may have noticed that the ponds in the Miami area are frequently covered with clumps of light-colored slime, what some might call “pond scum”. It might look pretty disgusting to the average person, but to those of us who study the Everglades it is very special stuff. We call it periphyton. It is a community of micro and macro-organisms that lives under the water surface in the Everglades, or floats if it accumulates enough bubbles of oxygen. Periphyton forms on the skeletons of flowering aquatic plants, particularly the bladderworts (genus Utricularia). As a community periphyton consists of a variety of organisms that live in the matrix of dead organic matter: bacteria, protozoans, green algae, diatoms, rotifers, insect larvae, and much more. We have added several pages of illustrations of organisms that you can easily find when you observe preparations with a microscope. This is also a good exercise for you to learn how to use a microscope.

Periphyton is ecologically important in the Everglades because it is the source of much of the carbon fixed in photosynthesis, and this is passed to other organisms, particularly apple snails and small fish, in food webs. The snails and fish are eaten directly by birds, or often by larger fish, that are then eaten by birds and alligators. So this is the stuff on which the Everglades runs. A number of scientists at FIU are studying the effects of adding phosphorus (a key ingredient in the water from the sugar cane farms to the north) on the function of the wetlands ecosystems. We are finding that even modest additions of phosphorus cause the periphyton to break apart. This may have unknown consequences for the function of this ecosystem, and we are trying to figure this out.

Periphyton

Dead material

Prawns

Crayfish

RotifersCopepodsInsect Larvae

Shellfish

Alligators

Wading Birds

Gar

Bass

Examining Periphyton Under the Microscope

In this laboratory exercise you will observe and identify organisms in the periphyton community, taken from an Everglades pond, and supplied to the classroom. This is an enjoyable process, because you may see amazingly bizarre living organisms swimming around in the water, or non-moving green and photosynthetic algae. Try to match what you see to the organisms illustrated here. Make a list of the organisms you have seen. If it is unusually interesting, share the view with your table partners.

Examining Microorganisms 

Take a piece of the periphyton mat without squeezing it and place it in a petri dish. (Sometimes there are flies in the periphyton that will bite if you squeeze the periphyton too hard). Place the dish on a dissecting microscope and examine the periphyton for macro-organisms. Use thefollowing diagrams to help you identify what you are observing. If possible, try to isolate a few of the more interesting organisms by using tweezers.

Adult Beetle

Clam or Mussel

Leech

Mayfly larva

Rotifer

Water Mite

Gammarus (Scud)

Copepod

Midge larva

Stonefly Larva

Hemiptera (Water Bug)

Snail

Examining Microorganisms

The microorganisms in periphyton belong to the Protista kingdom. Protists include all organisms that lack distinguishing characteristics of fungi, animals, or plants. They are the earliest eukaryotes and include unicellular and multicellular, plants and animals. They have simple cellular organization without specialized tissues. Protists live in almost any aquatic environment and some are important primary producers in ecosystems. Other protists are responsible for a variety of diseases including malaria and African sleeping sickness.

As you examine your periphyton, try to find Paramecium and Amoeba, two protozoan (animal-like) protists. Amoeba has pseudopods, movable extensions of the cytoplasm, that it uses for locomotion and gathering food. Paramecium, on the other hand, is surrounded by hair-like cilia that it uses for locotion.

In order to see micro-organisms present in the periphyton, it needs to be homogenized

(ground up or pureed), diluted with water, and examined under a compound light microscope. This has already been completed for you. Place one drop of homogenized periphyton on a microscope slide. Gently add a cover slip, by placing one edge against the slide and allowing it to fall over the tissue. This helps force out the air bubbles that tend to be trapped under the coverslip. You can remove excess water by twisting an end of a kleenex (or kimwipe) and placing it on the edge of the coverslip. It will absorb the excess water. Then place the slide on the microscope stage and begin your observations under low power (10X). Look for a variety of micro-organisms, as illustrated in the following pages, in the periphyton. You can boost the power by turning the nosepiece to a higher power objective (watch your instructor demonstrate this). You can estimate the size of the organism by comparing its length to the diameter of the field at any given magnification. If you see absolutely nothing, then try preparing another slide of periphyton, then look again.

 

PROTOZOANS

Volvox EuglenaPeridinium

GREEN ALGAE

Bulbochaete MougeotiaChlamydomonas

OedogoniumSpirogyra Ulothrix

DIATOMS

Fragilaria

Frustulia

Gomphonema

Navicula

Nitzchia

CYANOBACTERIA

Nostoc

Oscillatoria

DESMIDS

Desmidium

Experimenting on Periphyton

Using the techniques you have learned in the lab you could ask some interesting questions about periphyton, and collect observations consistent or inconsistent with the hypotheses stemming from these questions. Here are some sample questions.

1. Light levels at the top should be much higher than at the bottom of a floating mat of periphyton. Organisms adapted to different light intensities should be found at different levels in the mat. You could simply sample different levels of the mat and count the organisms you have observed.2. Organisms adapted to specific light levels may move vertically up and down in the mat during the day. You could count organisms at different levels and at different times of the day.3. Conditions, as water temperature and sunlight, change during the year. Periphyton organisms should change in abundance at different times of the year. Again, you could count organisms in mats at different times of the year.