THE MEIOBENTHIC COMMUNITY OF FRESHWATER ECOSYSTEMS RECEIVING ACID MINE DISCHARGES
The meiobenthic community is a diverse group of algae, protozoa and animals that live in the benthic zones of
streams, lakes, estuaries and oceans. This type of community is associated with the muds, sand grains, pebbles ,
stones and other materials that make up the benthic substrate of fresh and salt water ecosystems. Meiobenthic
organisms are usually microscopic and range in size from several microns to a millimeter or so in length. Some
algae that are considered meiobenthic are larger since individual cells form filamentous colonies that can be
longer than twenty centimeters. Meiobenthic communities are found in a variety of habitats which include a
wide range of environmental conditions, including meiobenthic organisms associated with deep sea vent zones.
In freshwater streams this community is dominated by algae (both single celled and filamentous), various
ciliated protozoa, and such animal groups as nematodes, tardigrades (waterbears) and rotifers. One relatively
specialized meiobenthic habitat is freshwater streams that are affected by the acid water discharges from
abandoned coal mines. Meiobenthic communities can thrive in these waters even with pH values between 2 –
3. The remainder of this paper describes the meiobenthic communities found in abandoned mine outflows in
the bituminous coal fields of Tioga County, northcentral Pennsylvania. The acid water (pH 2-3) from these
outflows has a detrimental effect on the larger aquatic organisms (fish and invertebrates) of the Tioga River
watershed. One mine outflow with a relatively robust meiobenthic community is Coal Creek, just to the east of
Blossburg, PA. This meiobenthic community is dominated by one filamentous algae, Klebsormidium, and two
species of diatoms in the genus Eunotia. Small flagellated, unicellular algae (golden-brown or chrysophyte
algae) can also be abundant. Ciliated protozoa such as Stylonychia , a nematode, two rotifers, Cephalodella and
Philodina, and a tardigrade are found in much smaller numbers in sediment samples. Other taxa can also be
found at different mine outflows. For example at the O99 mine that discharges into the Tioga River the
filamentous algae Entransia can be abundant in the summer and fall months. The following is a sample of the
common meiobenthic organisms that can be found in the mine outflows of Tioga County, PA. It should be noted
that once the pH exceeds 3 and the iron oxide (yellowboy) precipitates onto the substrates, the meiobenthic
communities are eliminated.
ALGAE
Klebsormidium: a filamentous green algae. Abundant at the Coal Creek site.
Two examples of single celled, flagellated chrysophyte (golden-brown) algae common in acid waters
The genus Chromulina
The genus Ochromonas
The following pictures are species of diatoms of the genus Eunotia. Diatoms are noted for the outer glass (silica)
encasement known as a frustule. The frustules of diatoms are of many geometric shapes and ornamented with
ridges, furrows and small holes.
PROTOZOA
Ciliated protozoa, like the genus Stylonychia shown here, are also important components of the meiobenthic
communities of acid mine waters. This genus is relatively common at the Coal Creek site.
The long cilia extending from the posterior of this one-celled protozoan is a feature of this genus.
ANIMALS
The Phylum Nematoda
This is a very diverse group of worms that can be found in great abundance in the soil and in aquatic
ecosystems. Most nematodes are free-living but a large number of them are parasites of other animals,
including man. Parasitic species in man can cause such conditions as river blindness, elephantiasis, hookworm
and a host of other conditions. Some nematodes are very tolerant of low pH environments. The vinegar eel or
worm is an example and it can live in moderate concentrations of acetic acid (vinegar). Below is a typical freeliving, aquatic nematode.
The Phylum Rotifera
This group of animals is found as a major component of the zooplankton in freshwater ponds and lakes. They
are also common in the benthic substrates of flowing water ecosystems. Some, like the two genera shown
below, have species that are low pH tolerant. A defining feature of the rotifers is that they have a ciliated organ
known as the corona surrounding the oral opening. The corona is used for locomotion and also to set up a
current of water into the oral area so that the organisms can filter prey and food particles out of the water.
Another interesting aspect of their life history is that the females can produce a viable egg that will grow into a
new female without fertilization by a male. This process is called parthenogenesis and all progeny produced are
females and genetic clones of the mother.
The genus Philodina –
note the corona on each individual
The genus Cephalodella
The genus Cephalodella
The Phylum Tardigrada (waterbears)
This group of animals is found in a diverse array of habitats ranging from the deep ocean floor to freshwater and
terrestrial habitats. In terrestrial environments they are associated with wet soils or streamside mosses.
Tardigrades are very hardy animals and can withstand very harsh environmental conditions. They can live in
low pH conditions, they can be dehydrated for longs periods of time and still be viable and they can be frozen to
subzero temperatures and still survive when thawed. These animals have four pairs of lobopodous appendages
that end in multiple claws. The body is somewhat inflated and has the general appearance of a “bear”, hence
the common name waterbears. Many waterbears can also reproduce, just like the rotifers, by parthenogenesis.