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James G. (James George) Needham.

The life of inland waters; an elementary text book of fresh-water biology for students online

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found in the
marginal zone of
the pond border,
but here they of-
ten cover large
areas in a nearly
pure stand. In
our latitude in the more permanent waters, the
dominant species usually are cat-tail, phragmites,
bur-reed and the soft-stemmed bulrushes; in the
shoals that dry up each year they are sweet flag,
sedges, manna grass and the hard-stemmed bul-
rushes. Such plants as these have strong inter-
laced roots and runners that form the basis of the marsh




FIG. 202. Tear-thumb.



344



Aquatic Societies



cover, and that support a considerable variety of more
scattering species. One of the most widespread of
these secondary forms is the beautiful marsh fern,
whose black root stocks over-run the tussocks of the
sedges, shooting up numberless fronds. Scattering
semi-aquatic representatives of familiar garden groups
are the marsh bellwort (Campanula aparinoides) , the
marsh St. John's wort (Hypericum virginicum) and the
marsh skull-cap (Scutellaria galericulata) : these are
dwarfish forms, however, that nestle about the bases of
the taller clumps. With them are straggling prickly
forms, such as the marsh bedstraw (Galium palustre),
the white grass (Leersia) and the tear- thumb (Polygo-
num sagittatum, fig. 202). Strong growing forms that
penetrate the marsh cover with stout almost vine-like
stems are the marsh five-finger (Potentilla palustris) the




FIG. 203. A marshy pool with flowers of the white water crow-foot rising
from the surface.



Marsh Animals 345



joint weed (Polygonum) and the buck-bean (Menyan-
thes trifoliata). True climbers also, are present in the
marsh although usually only on its borders; such are
the climbing nightshade bittersweet (Solanum dulca-
mara) and the beautiful fragrant -flowered climbing
hemp-weed (Mikania scandens). Here and there one
may see a protruding top of swamp dock (Rumex
verticillatus) , a water hemlock (Cicuta bulbifera) or a
swamp milkweed (Asclepias incarnata).

Every opening in the marsh contains forms that are
more characteristic of ponds and ditches, such as arrow-
heads and water plantain. And even the little trash
filled pools often contain their submerged aquatics.
Such a one is shown in the figure 203, a shallow pool
filled with fallen leaves, its surface suddenly sprinkled
over with little star-like flowers when the white water-
crowfoot shoots up its blossoms.

Algae often fill these pools; sometimes minute free-
swimming forms that tint their waters, but more often
"blanket algae," whose densely felted mats may smother
the larger submerged aquatics.

The animal life of the marsh is also a mixture of pond
forms and of forms that belong to the more permanent
waters. The fishes are bullheads and top minnows and
others that can endure foul waters, scanty oxygen and
rapid fluctuations of temperature. Of crustaceans,
ostracods and scuds are most abundant. Of molluscs,
Pisidium and Planorbis are much in evidence, and other
snails are common. Insects abound. Some are aqua-
tic and some live on the plants. Of all Odonata, Lestes
(fig. 204) is perhaps the most characteristic marsh inhabi-
tant ; of mayflies, Blasturus and Caenis ; stoneflies, there
are none. Of caddis-flies there are many, but Limno-
philus indivisus is perhaps the most characteristic marsh
species. It is not known to inhabit any waters except



346



Aquatic Societies



those that dry up in summer. The commonest beetles
are small members of the families Hydrophilidas,
Dytiscidae and Haliplidae. The most characteristic of

the bugs is the slen-
der little marsh-
treader, Limno-
bates. Swale-flies,
mosquitoes, crane-
flies and ubiqui-
tous midges abun-
dantly represent
the aquatic Dip-
tera.

There are, of
course, many in-
sects dependent
upon particular
plants. Such are
the tineid moth,
Limnacea phragmi-
tella, that burrows
when a larva in
the Typha fruit
spike, and the wee-
vil, Sphenophorus,
that burrows in the
Typha crown; the
leaf-beetle, Dona-
da emerginata,
whose larva feeds
on the submerged roots of the bur-reed, etc. Here are
also a number of characteristic spiders, such as the
diving spider, Dolomedes.

Doubtless the lower groups of animals possess species
that are addicted to dwelling in marshes, and fitted to
the peculiar conditions such places impose, but these




FIG. 204. A damselfly. Lestes uncatus.



Marsh Societies



347



have been little studied. There is hardly any situation
where the fauna is so imperfectly known.

As compared with the land, fauna and flora of
marshes are characterized by a small number of species,
and enormous numbers of individuals. In other words,




FIG. 205. "Tree-swallow pond": a once famous collecting ground in the
Renwick marshes at Ithaca. Photo taken in spring after the burning and
the freezing and the floods, but before the growth of the season.

the population is one of small variety but of great den-
sity. Such forms as are fitted to maintain themselves
where floods and fire alternately run riot find in the rich
soil and abundant light and moisture opportunity for a
great development. Fire sweeps the surface clear of
trees, which would overtop and overshadow the
herbage and would create swamp conditions. The
ground layer of water-soaked trash prevents the burn-



348 Aquatic Societies



ing of the root stocks; it also prevents deep freezing
after the fires have run. Plants that are capable of
renewing their vegetative shoots from parts below the
level of the burning, are the ones that year after year,
maintain their place in the sun.

Ill

Bog Societies. Bogs belong to moist climates and to
places where water is held continuously in an amount
sufficient to greatly retard the complete decay of plant
remains. Acids accumulate, especially, humous acids.
The soil becomes poor in nutriment, especially in
available nitrogen. Plants can absorb little water,
at least at low temperature; and the typical bog
situation is therefore said to be " physiologically dry."
With such conditions there go some striking differences
in flora and fauna. The plants are "oxylophytes" like
sphagnum and cranberry, i. e., plants that can grow in
more or less acid media, and that have many of the
superficial characteristics of desert plants; such as
vestiture of hairs or scales or coatings of wax, thickened
cuticle, leaves so formed or so closed together as to
limit or retard transpiration. The kinds of plants are
fewer; the individuals crowd prodigiously. They are
eaten by animals less than in any other situation.
Their remains, partly decomposed, are added to the soil
in the form of deposits of peat. The animal population
is correspondingly reduced and scanty.

Sphagnum. The most characteristic single organism
in such a situation is the bog-moss, Sphagnum (fig. 206;
see also fig. 59 on p. 147). This grows in cushion-like
masses of soft erect unbranched stems, that are in-
dividually too weak and flaccid to stand alone, but that
collectively make up the largest part of the bog cover.
The masses are loose and easily penetrated by the roots



Sphagnum



349



and runners of other stronger plants. It is the inter-
penetration of these that binds the bog cover together,
making it resilient under foot.

The leaves of Sphagnum are interspersed with cells
that are mere water reservoirs having porous walls.
Some of these leaves are deflexed against the stem and
make excellent capillary
conduits for water upward
or downward. Whether the
abundant supply be in the
air above or in the soil be-
low, these make provision
for the equitable distribu-
tion of it. Wherefore, these
masses of sphagnum become
water reservoirs, holding
their supply often against
gravity, and bathing the
roots of all the cover plants
that rise above the surface
of the bog.

Sphagnum belongs to the
shore, and it is quite incap-
able of advancing into the
water unassisted. But with

the help of stronger more straggling plants whose roots
and branches penetrate and interlace in its masses in
mutual support, it is able to extend as a floating border
out over the surface of still water in small lakes and
ponds. These floating edges may be depressed by the
weight of a man until they are under water, but they
are tough and elastic, and rise again unharmed when
the weight is removed. Long, strong, pliant-stemmed
heaths and slender sedges are the plants commonly
associated with sphagnum in the making of this floating
border. In the bog cover equally close is its association
with the common edible cranberry.




FIG. 206.



a b

Bog moss, Sphagnum;



a the tip of a spray; b, a. few cells from
a leaf; x, long interlaced lines of slen-
der sinuous chlorophyl-bearing cells, and
y, large empty water reservoir cells hav-
ing pores in their walls for admission of
water and annular cuticularisations
for support.



350



Aquatic Societies



Some habitual associates of sphagnum are shown in
figure 207. In such a place as the foreground of this
picture, if one slice the bog cover with a hay-knife, he




FIG. 207. A bit of bog cover. (McLean, N. Y.). From the central clump
of pitcher-plant leaves rises one long-stalked flower. The surrounding bog
moss is Sphagnum. A few slender stems of cranberry trail over the moss.
The taller shrubs are mainly heaths such as Cassandra and Andromeda.

(Photo by H. H. Knight.)

may easily lift up the slices; for they are composed of
living material to a depth of only about a foot. Below
is peat; at first light colored and composed of identifi-
able plant remains, but, deeper, becoming darker and
more completely disintegrated. The slices cut from



Bog Plants



351



the surface have sphagnum for their filling, but they are
tough and pliant, like strips of felt, owing to the close
interlacing of roots and stems of the other plants of the
bog cover.

Many delightful herbs grow on the surface of the bog.
The pitcher-plant shown in our figure is one, and the

sundew (see fig. 172 on p.
283) is another carnivor-
ous species. These, as we
have seen in the preceding
chapter, have their own
way of getting nitrogen when
the available supply is small.
Orchids of several genera
(Habenaria, etc.) and moc-
casin flowers (fig. 208) there
bear beautiful flowers. Cot-
ton grass (Eriophorum) is
showy enough with its white
tufts held aloft when in
fruit, and a beaked rush
(Rynchospora) is its natural
associate. In places where
the surface rises in little
hummocks, there are apt to
be patches of the xerophytic
moss, Polytrichium, associ-
ated with charming little
colonies of wintergreen and
goldthread. At the rear
of the heath shown in our figure stand huckleberries and
bog brambles and masses of tall bog ferns while thickets
of alder and dogwood crowd farther back.

Where sphagnum borders on open water, there often
lies in front of it the usual zone of aquatics with floating
leaves, as shown in the accompanying picture, and in




FIG. 208. A charming bog plant,
the moccasin flower. (Cypri-
pedium reginae).



352



Aquatic Societies



still deeper water there are apt to be beds of Chara and
of pondweeds. These and the molluscs associated
with them, leave their calcined remains deposited on
the pond bottom as a stratum of marl. Thus the




FIG. 209. Mud pond, near McLean, N. Y. This is a bog pond, surrounded
in part at least by floating sphagnum. The outlet (to left in the picture) is
bordered by tussock sedges, backed up by extensive alder thickets.

(Photo by John T. Needham.)

filling of a bog pond is in time accomplished by the
deposition of a layer of marl over its bottom, and a
much thicker mass of peat over the marl. Successive
stages in the filling process are graphically shown in
Dachnowski's diagram, copied on the next page.

Peat formation and filling of beds goes on, of course, in
ponds where there is no sphagnum; goes on wherever



Peat and Marl



353



the conditions for incomplete decay of plants prevail;
and from the foregoing it will be seen that peat is not
likely to be composed of the remains of sphagnum
alone. The forefront of advancing shore vegetation is
led by a number of plants of very different character.








FIG. 210. Dachnowski's diagram illustrating three stages in the filling
of a pond with deposits of peat and marl. Peat is stippled; marl,
cross-lined.

OW, open water; M, marginal succession; S, shore succession; B, bog succession,
including bog meadow (Bm), bog shrub (Bs), and bog forest (Bf); MF, mesophytic
forest.



354



Aquatic Societies






The accompanying diagram
shows five modes of progress into
deeper water of pioneer land-
building plants.

a is the method of the spike-
rush on gently sloping shore. It
is the method by which number-
less shore plants extend their hold-
ings, subterranean off-shoots.

b is the method of the tussock
sedges (see also fig. 209) which on
the loose mud in shallow waters
build up solid clumps. Many of
these, less than a foot in diameter,
are yet of such firmness that they
will sustain the weight of a man.
Every one knows such clumps,
from having used them (as step-
ping stones are used) in crossing
a swale. New offsets lie hard
against the old ones, roots descend
in close contact, and fibrous root-
lets interlace below in extraordin-
ary density.

c is the method of the swamp
loosestrife, Decodon, a method of
advancing by long single strides.
The tips of the long over-arching
shoots dip into the water, and
then develop roots and buds and
a copious envelope of aerating tis-
sue. If these new roots succeed



FIG. 211. Diagram illustrating the method of
advance into deeper waters of typical land-
building plants.

a. Spike rush; b, tussock sedge; c, swamp loose-
strife; d, cat-tail flag; e, Sphagnum and hea th s.



Land-building Plants



355



in taking a good hold on the bottom, then other shoots
spring from this new center and repeat the process.

d is the method of the cat-tail flag. It consists in
developing an abundance of interlaced fibrous roots,
and then simply floating on them. Much mutual sup-
port is required by plants that grow so tall ; and any
great advance of a few clumps beyond the general front
may result in disaster from overturn by winds.

e is a method of mutual support between species of
very different sorts. It is that of the sphagnum and
heaths just discussed. Greater progress over 'deep
water is made by this method than by any of the others.

A photograph of the first named is reproduced as
figure 212.

FIG. 2 12. A bit

of running
root-stock of
a spike rush.
Eleocharis
pa lustris,
showing its
method of ad-
vance over the
pond bottom.
Branching
subterranean
off-shoots ex-
tend down a
sloping shore
until they
reach a depth
of water in
which they
cannot func-
tion effec-
tively.




356 Aquatic Societies

IV

The population of stream beds If we distinguish
between lenitic and lotic societies by presence or
absence of growths of vascular plants, then the greater
part of stream beds shelter lenitic societies. The
greater part has not a current of sufficient swiftness to
prevent the growth of such plants. And indeed it is
only in restricted portions of any stream that we
find the animals specially adapted to meet conditions
imposed by currents.

Where the stream bed forms a basin, there the condi-
tions of life, for the larger organisms at least, approxi-
mate those of a lake. Hence we find in those places
in large streams where the water is deep and still, there
occur many forms like those in lakes. The sturgeon
belongs in both, and so do the big mussels and the
operculate snails, the big burrowing mayflies, the big
tube dwelling midge larvae, etc. The basins of creeks
offer conditions like those in ponds; the basins of
brooks, conditions like those of pools. And the largest
species are restricted to such of the larger basins as can
afford them adequate pasturage and suitable places for
rearing their young. To be sure, in all those basins,
the water is constantly passing on down stream and
the planet on of the basin, while in part developing there,
is in a large part constantly lost below and constantly
renewed from above. Kofoid (08) states that "The
plancton of the Illinois River is the result of the
mingling of small contributions by tributary streams,
largely of littoral organisms and the quickly growing
algas and flagellates, and of the rich and varied plancton
of tributary backwaters, present in an unusual degree
in the Illinois because of its slightly developed flood-
plain, and from which it is never entirely cut off, even
at lowest water. * * * * To these elements is added
such further development of the contributed or indigen-



The Population of Stream Beds 357

ous organisms as time permits, or the special conditions
of nutrition and sewage contamination facilitate.
Though continually discharging, the stream maintains
the continuous supply of plancton, largely by virtue of
the reservoir backwaters the great seedbeds from
which the plancton-poor but well fertilized contribu-
tions of tributary streams are continuously sown with
organisms whose further development produces in the
Illinois River a plancton unsurpassed in abundance."

Doubtless, in every stream the plancton supply is
constantly renewed from sheltered and well populated
basins, which serve as propagating beds. And, indeed,
on every solid support diatoms are growing, and the
excess of their increase is constantly being released
into the passing current. In the swiftly flowing,
plancton-poor streams about Ithaca there is not time
for much increase of free planctons by breeding. The
waters run so swift a course they can only carry into
the lake such forms as they have swept from their
channels in their rapid descent.

While there has been much study of the life of the
open waters of rivers there has hitherto been little
study of their beds. Where the beds are sandy with
flow of water over them we know the life differs from
that of muddy basins. The heavier-shelled mussels and
snails are on the sand ; and the commoner insects there
are the burrowing nymphs of mayflies and Gomphine
dragon-flies, and the caddis-worms that live in portable
tubes of sand.

The beds of the smallest streams are easy of access,
and a few observations are available to indicate that
their study will bring to light some interesting ecological
relations. A few very restricted situations will be cited
in illustration.



358



Aquatic Societies



Moss patches On
the rocky beds of
large brooks that run
low but do not en-
tirely run dry, there
are frequent patches
of the close-growing
moss, Hydrohyp-
num. These patches
frequently cover the
vertical face of a
waterfall (fig. 213).
The little water that
remains in dry season
trickles through the
layer of moss, and
in times of flood the
speedier torrent
jumps over it. Under
the flattened frond-
like green sprays
there is compara-
tively quiet water
at all times; and in
this situation there
lives a peculiar as-
semblage of insects
that differ utterly
from the lotic forms

dwelling in the same streams (to be discussed in a later
part of this chapter), tho often dwelling within a few
feet of them. They lack all the usual adaptations for
meeting the wash of currents. They are (with occa-
sional intermixture of a few larvas of small midges
and of Simulium) the following:




FIG. 213. A moss-bed covering the face of a
rock ledge (in flood time, a waterfall) in
the bed of Williams Brook at Ithaca,
N. Y. The water seen on the rock above
trickles down through this moss. Here
is a restricted and peculiar animal pop-
ulation.



Moss Inhabitants



359



1. The slender larvae of soldier-flies (Euparhyphus
brevicornis). Each bears a pair of ventral hooks that
may serve for attachment.

2. The greenish larvae of the cranefly (Dicrano-
myia simulans).

3. The warty-backed larvae of the Parnid beetle
(Elmis quadrinotatus) .

4. Larvae and pupae of a little black Anthomyid fly
(Limnophora sp.?).




FIG. 214. Insect larvae from a moss patch such as is shown in the
preceding figure, a, Psychoda; b, Elmis; c, d, e, Euparhyphus, c,
being lateral, d, dorsal and e, ventral views, c and e show the huge
ventral hooks on the penultimate segment; /and g, cases of an un-
known caddis- worm, /, composed mainly of sand; g, mainly of moss.



360



Aquatic Societies



5. The slender larvae of a moth fly (Psychoda alter -
nata), its body covered with deflexed spines.

6. The larvae of an unknown caddis-fly whose cases
are composed sometimes of stones, sometimes of moss

fragments.

Leaf -drifts In the beds of wood-
land brooks, there are barriers of
fallen leaves, piled by the current
upon the bare, obtruding roots of
trees. These leaf -drifts have a
population of their own, the most
characteristic member of which
about Ithaca is the huge larva
shown in figure 215. This is the
larva of the giant cranefly, Tipula
abdominalis . Associated with this
larva in these water-soaked masses
of leaves, are the nymphs of such
stoneflies as Nemoura and of such
mayflies as Baetis and Leptophle-
bia, a few beetles and often many
scuds (Gammarus) . In the mud
behind the leaf -drifts, there are
often earthworms, washed down
from fields above.

In the clear pools in upland
streams that flow through swampy
woods, when the bottom is strewn
with forest litter intermixed with brownish silt, there
dwell a number of forms that certainly belong totheleni-
tic rather than to the lotic societies. Such are the caddis-
worms of figure 216. With these are associated small
mussels of the genus Sphaerium, squat dragonfly
nymphs of the genus Cordulegaster, and climbing
nymphs of the genus Boyeria, water-skaters on the



FIG. 215. Two larvae of
the giant cranefly, Tip-
ula abdominalis, an in-
habitant of leaf-drifts in
woodland brooks.
Natural size.



Leaf-drifts



361



surface and burrowing mayflies in the beds, and a con-
siderable variety of the lesser midges on every possible
support.

We have already noted (page 86) that slack water
exists behind boulders and other obstructions in the
bed of rapid streams: but this is not stagnant water;
and the animals living in such shelter, if the current
above them be swift, are hardly ever of the same species
that are found in ponds. Only in slow-flowing waters,
where conditions merge, do lotic and lenitic forms
become near neighbors.




FIG. 216. A bit of the bed of a pool in a woodland stream show-
ing among the forest litter the wooden cases of the larva, of the
caddis-fly, Halesus guttifer. (See also fig. 104 on p. 198.) Pro-
tective resemblance. There are 14 cases in the picture.



362



Aquatic Societies



A DIAGRAM OF LOCALIZATION OF INSECTS IN
THE BED OF A SWIFT STREAM

(From Needham and Christenson, '27)



surface




bottom



Twelve situations about a boulder, and the insects commonly found in
them in Logan River, Utah, are as follows:

1. Simulium; black fly larvae; fully exposed where current is swiftest.

2. Brachycentrus ; caddis worms; in square cases attached by the upstream

end.

3. Bibiocephala ; net- winged midge-larvae; of limpet-form, adhering by

ventral suckers.

4. Glossosoma; caddis worms, in pebbly cases on down-stream face of

boulders.

5. Antocha; carnivorous cranefly larva; in tubes on down-stream face of

boulder.

6. Hydropsyche; net-spinning caddis worm, making nets beside a crevice

where water breaks over.

7. Atherix; snipe fly larva, living in crevices.

8. Baetis and Leptophlebia; mayfly nymphs, living on bottom in slackened

current.

9. Iron and Rithrogena; mayfly nymphs, clinging to broad surfaces, mostly

underneath.
10. Chironomus and Tany tarsus; midge larvae, living in tubes in more or

less exposed places.
n. Ephemerella grandis, the prickle-back mayfly nymph; clinging to trash

in half sheltered places.
12. Acroneuria and Pteronarcys; stonefly nymphs; living amid the trash and

sheltered by it.
The arrow indicates direction of the current.




LOTIC
SOCIETIES



CCORDING to the
grouping outlined on
page 315, we designate
by this name those as-
semblages of organisms
that are fitted for life
in rapidly moving water
that are washed by
currents, as the name
signifies. Whether the
water flow steadily in
one direction as in
streams, or back and

forth with frequent shifts of direction as on wave-
washed shores, the organisms present in it will be much
the same sorts. The plants will be mainly such algae
as Cladophora, and slime-coat diatoms: the animals
will be mainly net-spinning caddis-worms and a variety


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Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 20 of 26)