226
NOTES AND COMMENT
it seems reasonable to expect that the major
non-seasonal changes
are linked to major
variations in the surface wind circulation.
The events of 1941 could be interpreted as
indicating an abnormal weakening of the
trade wind circulation (Wooster 1960). The
low temperatures of 1950-51 could result
from stronger than usual southerly winds
along the Peruvian coast. The recent work
of Bjerknes ( 1959 ) , Roden and Groves
( 1960)) Roden and Reid ( in press) and
others tends to support such an interpretation, although temperature - wind correlations do not yet give as clear-cut an answer
as one might wish. Unfortunately
in the
southern hemisphere the supply of reliable
historical weather data seems to be small.
If usable data can be located, it seems likely
that the picture of yearly change suggested
by these surface temperature isograms will
be relatively simple to explain.
FOOTNOTE
Since completion
of this work,
Schweigger
( 1959; Fig. 6 A, 6 B ) has published surface temperature isograms for the period 194S-1956 based
on a somewhat
different
interpretation
of the
same data.
WARREN s. WOOSTER
Scripps Institution of
Oceanography,
La Jolla, California
LIGHT
ATTENUATORS
REFERENCES
B JERKNES, J. 1959. The recent warming of the
North Atlantic.
Zn Bolin, B. (Ed. ), The Atmosphere and the Sea in Motion.
New York:
Rockefeller
Institute Press, pp. 65-73.
LOBELL, M. G. 1942. Some observations on the
Peruvian Coastal Current.
Trans. Amer. Geophys. Un., 2: 332-336.
POSNER, G. S. 1957. The Peru Current.
Bull.
Bingham Oceanogr. Coll., 16: 105-155.
RODEN, G. I. AND G. W. GROVES. 1960. On the
statistical
prediction
of ocean temperatures.
J. Geophys. Res., 65: 249-263.
AND J. L. REID, JR. Sea surface temperature, radiation,
and wind anomalies in the
North Pacific Ocean.
Rec. Oceanogr. Wks.
Japan (in press ).
SCHWEIGGER, E . 1942. Las irregularidades
de
la corriente de Humboldt
en 10s adios 1925 a
1941. Una tentativa de su explication.
Bol.
Compafiia Admin. Guano, 18: 27-42.
-.
1959. Die Westkiiste
Siidamerikas
im
Bereich des Peru-Stroms.
Heidelberg-Miinthen:
Keysersche Verlagsbuchhandlung.
513
PP.
SEARS, M. 1954. Notes on the Peruvian coastal
current.
1. An introduction
to the ecology
of Pisco Bay.
Deep-Sea Res., 1: 141-169.
VOGT, W.
1942. Informe elevado a la Compa%a Adminstradora
de1 Guano.
Lima, Compafiia Admin. Guano, 18: 1-132.
WOOSTER, W. S. 1960. El Nifio.
Calif. Coop.
Ocean. Fish. Invest., Rep., 7: 43-45.
FOR USE IN PHYTOPLANKTON
A study of the response of phytoplankton
to variations of light intensity is becoming
increasingly important in primary productivity research, both in lakes and in the
ocean. In all such work we need to illuminate bottles of water containing algae to
a light intensity which is a known fraction
of that of an incident light source which
may be daylight or some artificial form of
illumination.
It is more difficult than might be supposed to contrive a convenient attenuator,
the coefficient of which is easily reproducible, can be varied over a wide range and is
constant with time. The attenuator should
be robust, unaffected by water and truly
PHOTOSYNTHESIS STUDIES
neutral in its spectral behavior. Fogged
photographic film or plates, even with protective coatings, have few of the above
desirable characteristics.
If light is blocked off by wire gauze of
fine mesh size the attenuation is truly neutral and the system can be made robust
and immersed in water for reasonable periods of time with no deterioration.
Furthermore, provided that the mesh size of the
gauze is sufficiently
small, the effect of
more than one layer of gauze is additive,
that is to say if the fractional transmission
of one layer of gauze is T the attenuation
of two layers is approximately T2 etc., up
to at least four layers.
NOTES AND COMMENT
\
zzi
n
n
Do
A
END
B
C
CONNECTING
#I50 MONEL
PLATE
(24
ROD ( l/8” DIAMETER
MESH(I--4LAYERS)
A light
0
MONEL)
D 8.O.D. BOTTLE TRAY 1 BLACK)
E HOLES IN BOTTOM OFTRAY.
FIG, 1.
0
U.S.G. MONEL)
attenuator,
Qs’
showing
0
also its use in a tray from a water-cooled
This forms the basis of the neutral filters
shown in Figure 1. The “light incubators”
used by us for photosynthetic
work are
designed to hold black-painted trays with
perforations in their base which allow cooling water to flow up through the equipment. The trays, which are illuminated
from above, hold 300-ml B.O.D. (biological
oxygen demand) bottles which we use for
both oxygen and Cl4 photosynthetic
rate
measurements.
The filters consist of one or more layers
of 150-mesh Monel metal screen wrapped
over a Monel metal frame of rods and
plates, as shown in the diagram, and soldered to the bottom rods and to the endplates. B.O.D. bottles fit snugly into this
assembly which will rest in the compartments of incubator trays (as shown) or can
be used anywhere where a flow of cooling
water is available. Bubbles may tend to
collect on the outer surface of the mesh
when water is flowing but can be easily
dislodged. As a precaution it is perhaps
best to pass cooling water through a bag
made of 150-mesh Monel screen before it
enters the incubator but we have found no
0
incubator.
evidence of clogging or deterioration
of
filters in continual use throughout
one
summer. They should be rinsed with fresh
water and stored dry.
The percentage transmission of light is
surprisingly
uniform over the base of a
filter and amounts to about 35% for one
thickness of screen, 13% for two thicknesses, 5% for three thicknesses and 2% for
four thicknesses. The variation from filter
to filter does not exceed 5-10% of the absolute amount and changes very little with
time. We do not recommend the use of
five layers of screen but a flat “filter”
of 150-mesh Monel may be placed over one
or more compartments in a tray. This effectively multiplies the transmission of each
filter thus covered by a further 0.35.
The gap between 100% transmission and
the first Monel filter (with 35% transmission) is rather large. However, a filter
with about 65% transmission can be constructed using galvanized
screen made
from 16 x 12 mesh S.W.G. 33 wire. Doubtless similar materials could be found to
give transmissions greater than 65%. Gal-
228
NOTES AND COMMENT
vanized iron wire, protected by an acrylic
spray treatment, has proved to have adequate corrosion resistance.
Attenuators should be calibrated in situ
whenever possible. The exact fraction of
the light cut out by the screens will vary
somewhat with the equipment used and the
nature of the light source, in particular
THEECOLOGY
OF URNATELLA
whether or not the light reaching the
screens is parallel or diffuse.
C. D. MCALLISTER AND
J. D. H. STRICKLAND
Fisheries Research Board
of Canada,
Pacific Oceanographic Group,
Nanaimo, B. C.
GRACILIS
DISTRIBUTION
Rogick and Van Der Schalie (1950) erroneously referred to UrnuteZZu gracilis as
being exclusively North American. Damas
( 1938 ) , however, reported its occurrence
in the Meuse River in Belgium, and this is
apparently the only record of its occurrence outside of North America. U. indica,
the other species within the genus, was
described by Seshaiya (1947) from specimens collected in southern India. These
two species constitute the reported freshwater endoproctan fauna of the world.
Leidy ( 1851) d escribed U. gracilis from
specimens taken in the Schuylkill River in
Pennsylvania.
Subsequent collections at
the original collecting site were taken by
several authors including Allman ( 1856).
Leidy ( 1884) mentions its occurrence in
the Scioto River, Ohio, on the basis of
remnants of specimens found on a unionid
shell sent to him by Lea in 1883.
At the turn of the century, Kofoid ( 1898,
1908) recorded U. gracilis from the Illinois
River near Havana, Illinois.
In several
papers between 1921 and 1928, Richardson
also recorded the species from the Illinois
River. Specimens have been reported from
the Licking River in Kentucky by Williams
(1930). Rogick (1936) reported the species from several Lake Erie locations, and
in the same paper she commented on specimens collected in the Clinton River in
Michigan.
Rogick and Van Der Schalie
( 1950) reported U. gracilis from the Grand
River above Ionia, Michigan, and from the
Tippecanoe River near Pulaski, Indiana,
Davenport
(1904) mentioned the occurrence of specimens in the Mississippi Val-
LEIDY:
PHYLUM
ENDOPROCTA
ley but gave no evidence of collections or
authority.
There are two observational reports of
U. gracilis. One of these was by Dr. B. B.
Harris at Lake Dallas, Texas, and the other
by Dr. R. C. Osburn from specimens seen
in the Mississippi
River near Fairport,
Iowa.
My first collections of U. gracilis were
taken at Mile 598 (598 miles downriver
from Pittsburgh, Pa.) in the Ohio River
just above Louisville, Kentucky in September, 1958. Examination of bottom collections taken the previous year disclosed
many specimens of U. gracilis at Mile 596.
Since then I have taken additional specimens from bottom samples at Miles 113.7,
326.0, 443.8, 458.0, 600.0, 617.0, 618.0 and
630.0. Thus, it is to be found over a 500mile stretch of the Ohio River.
All of my collections were made in
regions of unidirectional
currents flowing
between % and 5 m.p.h. All other collections on record, with the exception of the
Lake Erie collections of Rogick and Van
Der Schalie ( 1950), were taken from flowing waters.
U. gracilis is characteristically
found
attached to rocks, sticks, and molluscan
shells. I have found as many as 1,000 or
more specimens on a 3-in. rock. Many
specimens were taken from Amblemu shells
and a few were found on the shells of PZeurocera caniculatum.
All specimens were
found in regions of coarse gravel, rubble
or boulders. None were found on sand or
mud bottoms.
Hydra americana was found associated
with U. gracilis on practically all occasions.