Acknowledgements
I would like to thank the entire staff of Hopkins Marine
Station for their valuable assistance and encouragement,
especially Dr. Malvern Gilmartin, Dr. John Martin, Mr. Robin
Burnett, and the crew of the R/V Proteus.
This work was made possible by grant GY 8950 of the
Undergraduate Research Program of the National Science
Foundation.
C
O
O
Abstract
Plankton samples from the surface and from 10 meters
depth were collected in Monterey Bay and analyzed for Ag,
Zn, Cu, Cr, Mn, Cd, and Pb. The results showed a trend
toward higher concentration at the air-sea interface.
Possible mechanisms of concentration processes are discussed,
with some consideration given to the ecological implications.
3
Introduction
Because of the unique properties of the air-sea interface,
it is surprising to find a paucity of information concerning
the biology of this zone. It has been stated that chemical
reactions in the ocean are "largely determined by phenomena
which occur at interfaces" (Horne, 1969), and that almost all
physical, chemical, and biological processes in the ocean
depend on the ocean having a free boundary with the air
(Wellander, 1961).
Study of the air-sea interface would probably provide a
good deal of information concerning the movement of heavy metals
in the ocean. There is now good evidence that a significant
portion of lead now entering the ocean does so via the atmos-
phere; automobile exhaust has been found to contribute greatly
to atmospheric lead pollution (Patterson, 1965, 1970; State
of Cal. Air Resources Board, 1967; Mauchline and Templeton, 1964;
Tatsumoto and Patterson, 1963). The interface is in constant
exposure to such atmospheric fallout. Moreover, the physical
and biological properties of the surface are such that materials
are either concentrated or dispersed there. Materials in the
surface layer are either heavier or lighter than sea water
(Wilson, 1959); materials that are lighter float to the surface
while heavier particles sink to deeper levels. Organisms
facilitate both of these processes. They carry materials to
the surface during their diurnal and seasonal migrations.
1
(Kuenzler, 1969 a,b). Also, small bubbles such as those
produced by plants during conditions of high photosynthesis,
and more importantly those produced by wave action, carry
organic matter to the surface through a process of adsorption
onto the surface of these bubbles. This process results in
the formation of surface organic slicks(Riley, 1963; Riley,
et.al, 1964; Siegel and Burke, 1965; Wilson, 1959; Blanchard,
1964; and Baylor and Sutcliffe, 1963). Materials move down-
ward, again via plankton migrations, and also by elimination
of waste products and detrital matter (Fowler and Small, 1967;
Kuenzler, 1969 a,b; Martin, 1970; and Osterberg, et.al., 1963).
It is likely that organisms living at or migrating to the surface
of the ocean are important in both the concentration of heavy
metals at the surface and transport to the ocean floor as a
phase of the biogeochemical cycling of the various elements.
Also, because heavy metalss are generally surface¬
active materials, and the surface of the ocean is a natural
area where these types of materials accumulate (Blanchard,
1964; Baylor and Sutcliffe, 1963; Riley, 1963; Riley, et.
al., 1964; Siegel and Burke, 1965; and Wilson, 1959), it
is reasonable to suspect that heavy metals may be concen-
trated at the surface of the ocean, relative to amounts
found in the underlying water.
The purpose of this study is to compare the concentrations
of Pb, Mn, Ag, Zn, Cd, Cr, and Cu in organisms collected
at the surface of Monterey Bay as compared to organisms
collected at a depth of about 10 meters. Several different
kinds of organisms were sampled and analyzed (calanoid
copepods, the euphausid Euphausia pacifica, the ctenaphore
Pleurobrachia bachii, and the siphonophore Velella lata);
surface samples were designated as neuston, and subsurface
samples labelled plankton.
half hour
taker
W
between 7:00 A.M. and 10.00 A.M. Boat spead was recorded
and used in the calculatiens of relative biomass density
While en board, the fresh samples were taken from the
net and plaeed in aeid-eleaned (4-6 M Hno,) glaseware,
cevered with aluminum foil, and stored en ke.
In the lab, major groups of organisma vere separate
This usually consisted of separating calaneid eoperod
from P. bachij and medusae (especially Oetatina sp.)
This was sasily done by passing the sample through a
coarse (0.5 gm. mesh) net. The remaining sample was
streined through a ring of phytoplankten netting, retai.
the copeped segment of the sample. Excess water was remove
nd wat weights recorded. All samples were driel at
for at lesat 24 hours.
Materials and Methods
Basic means of collection were a neuston sled towed
at the surface (David, 1965) anddsmall zooplankton net
simultaneously towed about 10 meters below the surface.
The two nets had openings of similar are (0.0h6 m for
the sled, 0.061 m for the plankton net) and similar
mesh (220.5 microns for the sled, 291 microns for net).
The sled was either towed off to the side of the
boat by means of a boom, or was trailed far enough aft
so that the wake had little effect. Tows lasted from
one-half hour to one hour. All inshore tows were taken
between 7:00 A.M. and 10:00 A.M. Boat speed was recorded
and used in the calculations of relative biomass density.
While on board, the fresh samples were taken from the
net and placed in acid-cleaned (1-6 N HNO,) glassware,
covered with aluminum foil, and stored on ice.
In the lab, major groups of organisms were separated.
This usually consisted of separating calanoid copepods
from P. bachii and medusae (especially Octatina sp.).
This was easily done by passing the sample through a
coarse (0.5 cm. mesh) net. The remaining sample was
strained through a ring of phytoplankton netting, retaining
the copepod segment of the sample. Excess water was removed
and wet weights recorded. All samples were dried at 80°0
for at least 21 hours.
Aliquots of the dried samples (less than l gm dry
weight) were placed in acid-cleaned beakers and dissolved
in concentrated HNO, (70-90%). Organic matter was destroyed
using a modification of a method described by Middleton
and Stuckey (in Christian and Feldman, 1970). The modified
method consisted essentially of heating the sample with
concentrated HNO,, evaporating the solution to dryness,
redissolving the ash in acid, then adding a few ml of
HoO, (30%) to oxidize any remaining organic material. A
blank was included for each set of samples as a check for
reagent contamination.
After the sample was totally mineralized, the remaining
ash was dissolved in concentrated HNO, and diluted to a
standard volume with distilled H.0. The samples were then
analyzed for Ag, Zn, Cr, Cu, Mn, Cd, and Pb on an atomic
absorption spectrophotometer (model 303, Perkin-Elmer).
3/
damelty vis re
Results
Results from the analyses of three inshore and two
offshore tows are presented in Table I and Figure I. The
Vellela lata sample examined was taken from samples collected
about 100 miles off the Oregon coast during a cruise of the
R/V proteus in October, 1970. Highlights of the results follow.
1. The calanoid copepod samples collected at the surface
had higher concentrations of Ag, Zn, Pb (p =.20; see Table
II), and Cr (p = .10) than samples collected at 10 meters
depth, while Cd concentration was higher in the plankton (p -.10).
2. Offshore plankton copepods had over twice the Pb concen-
tration (10.37 £ 1.61 ppm vs. 1.28 - 1.12 ppm; see Table I)
as that found in the inshore plankton copepod samples (p =.01).
3. Euphausia pacifica samples at the surface and at 10 m.
showed no significant difference (all p values greater than
20) in heavy metal concentration except for Pb, for which
the plankton samples had about twice the neuston Pb concen-
tration (5.39 I .56 vs. 2.15 -.32, p -.05).
1. There was no significant difference measured for any
heavy metal concentration between neuston and plankton
samples of Pleurobrachia bachii (all p values greater than.30).
5. As the relative density of copepods in the surface zone
decreased in a series of runs, a corresponding increase in
C
plankton density was recorded (see Figure II).
6. There is an inverse correspondence between Od concen-
tration and relative biomass density in plankton copepods.
and a positive correlation between density and Cd concen-
tration in neuston copepods. Also, there are inverse
correlations for Pb and Zn vs. density in neuston copepods.
Discussion
Results of this study do not show with certainty a
process of heavy metal concentration at the air-sea interface.
The probable reason for this is that the organisms sampled
were members of a vertically migrating population rather
than members of distinct neuston and plankton communities.
Despite this, however, there was a trend toward higher
concentrations in the surface copepod samples over those
samples collected at 10 m. This strongly suggests that
some heavy metals are concentrated at the interface. It
is interesting that this trend is in the opposite direction
to that found by Martin (1970), who reported higher heavy
metal concentrations in copepod sampled at depths greater
than 100 m. than in samples from surface waters. This
apparent disparity may be related to the depth of sampling.
The purpose of this study was to was to analyze movements of
heavy metals at the air-sea interface and immediate underlying
waters, while Martin was looking at larger scale movements.
His "surface water" sampling zone included both zone sampled
in this study. Despite this, there is fairly good agreement
between values reported here and those given by Martin (Table Il1
Additional evidence for the phenomena of surface concen¬
tration comes from the results of Baxter (1971) on these
same copepod samples for analysis of DDT. He noted that
the surface samples had a greater concentration of DDT than
did the plankton samples. Also, Marion (1971) reported that
O
320
the DDT concentrations in Hermissinda crassicornis collected
from floats were 2.3 times higher than those collected pilings,
0.5 to 7 m. below the surface.
Offshore planktonic copepods had significantly more
Pb than the inshore planktonic copepods, for reasons as yet
unknown.
An anomalous set of data resulted from analysis of the
Euphausia pacifica samples collected during tow 15. For
six of the metals analyzed there was no significant differ-
ence between the surface samples and those collected at 10 m.
Moreover, Baxter (1971) found that the two samples had the
same DDT concentrations. This homogeneity for E. pacifica
might be expected because this organism is a strong vertical
migrator, and may move from a depth of several hundred meters
up to the surface. However, the 10 m. samples contained
about twice the Pb concentration of the surface samples.
Physiological differences between the populations are not
considered likely because they would tend to produce more
than a difference in the concentrati on of just one metal.
It is quite possible that, because only two samples were
analyzed, and that the concentrations of Pb measured were
at the limit of sensitivity for measurement by atomic absorp-
tion, the statistical test for this particular case was not
valid.
The neuston and plankton samples of Pleurobrachia bachii
showed no significant differences with respect to heavy
32
metal concentration. This is not surprising. P. bachii
is capable of strong and rapid vertical migrations; they
will move down when surface conditions are rough, and also
when light intensity is high (Hyman, 1940). Also, because
their surface area to volume ratio is minimal, P. bachii
does not concentrate high levels of heavy metals by surface
adsorption. Therefore, if differences between surface and
subsurface samples do exist, they are more difficult to
observe.
It is reasonable to expect an inverse relationship
between plankton vs. neuston density for the copepod samples
because copepods exhibit vertical migrations. The results
presented in Figure II indicate that both the neuston and
plankton samples were at least partly composed of a vertically
migrating population. But it is likely that some organisms
spend most of their time at the surface, while other organisms
seldomly leave the subsurface zone, because copepods were
always found in both zones during simultaneous tows at the
surface and 10 m. Copepods collected at the surface when
relative density was low are probably those organisms having
a long residence time on the surface. Similarly, samples
collected at 10 m. during low density conditions contained
those copepods that rarely migrate to the surface. The
existence of either of these populations is masked when density
is high.
This is the type of subdivision one might expect within
322
a large population; while the majority of organisms will
show an average amount of migration, some individuals will
be skewed on either the high or low side of the mean distance
and frequency of migration. There is evidence for some of
the differences occurring between individuals in a copepod
population. It has been noted that female copepods come to
the surface to lay eggs, and also that females migrate more
regularly than males (Marshall and Orr, 1955). Bainbridge
(1952, in Marshall and Orr) observed that some copepods may
inhabit only the top 30 cm. of water, while others seldoml
migrate that close to the surface.
It is reasonable to suspect that some copepods spend
much of their time at the surface, while others more exclusively
inhabit the subsurface zone. If there is a difference in
metal concentration between the surface and subsurface,
those organisms that spend the greatest amounts of time at
each zone should exhibit those differences most clearly.
There is good evidence that this is true. Relative density
is inversely related to time; a low density value gives
some measure of the length of time certain organisms spent
in one zone. Figure IIIdemonstrates some relationships
between metal concentration and residence time, as measured
by relative density. From these relationships one can gain
some knowledge as to the depths at which various metals are
concentrated.
322
The relationships for Cd concentration vs. density Fiqve lLb)
are especially interesting. In the plankton samples,
concentration increases as density decreases; that is,
concentration increases as residence time increases. The
opposite is true for neuston copepods; concentration increases
as density increases. This type of relationship might occur
if Cd is in higher concentration in subsurface waters than
at the surface. Organisms that remain at depth for a longer
period of time would tend to concentrate the metal through
adsorption and feeding. Also, as copepods that have spent
some time in the subsurface waters migrate to the surface,
they carry with them relatively high Od loads. So concentra-
tion of Od in neuston increases while density also increases.
It is interesting to note that Cd is the only metal tested
that showed a higher concentration in the subsurface samples.
Zn and Pb concentrations in neuston copepods show the
same type of relationship demonstrated by Od in the plankton.
There are no corresponding relationships in the subsurface
samples for these metals, however. The probable reason for
this lack of correspondence is that the downwardly migrating
copepods diffuse throughout several meters of the subsurface
waters so that there is no clear gradient. These results do
support the hypothesis that at least Zn and Pb are concentrated
at the air-sea interface.
Conclusion
The results presented here favor the hypothesis that certain
heavy metals are concentrated at the air-sea interface relative
to concentrations found in underlying waters. Problems encountered
in sampling, analysis, and population structure of the plankton
tended to mask these differences.
The implications from this surface concentration effect may
be significant. It is likely that organism feeding on this surface
layer, such as larval fish and birds like skimmers and phalaropes,
may be receiving a relatively high metal load in their food.
Metals concentrated at the surface may feed directly into both
aquatic and terrestrial food webs. Also, because of the chemical
reactions that place at the surface, the concentration effect at
the interface may play an important role in the biogeochemical
cycling of these elements.
References Cited
Baxter, K.G., (1971), "Comparison of DDT residue values of
planktonic organisms at the air:water interface and subsurface
levels of Monterey Bay", (Unpublished MS on file at Hopkins
Marine Station Library)
Baylor, E.R. and W.H. Sutcliffe, Jr., (1963), "Dissolved organic
matter in sea water as a source of particulate food", Limnol.
Oceanog. 8: 369-371.
Blanchard, D.C., (1964), "Sea-to-air transport of surface active
material", Sci 116: 396-7.
Christian, G.D. and F.J. Feldman, (1970), Atomic Absorption
Spectroscopy. Wiley-Interscience, N.Y.
Cox, L.J., (1971), "DDT residues in sea water and particulate
mater in the California current system", Fish. Bull. (in press)
David, P.M. (1965), "The neuston net; a device for sampling the
surface fauna of the ocean", J. Mar. Biol. Assoc, U.K. 15:
313-320.
Fowler, S.W. and L.F. Small (1967), "Moulting of Euphausia pacifica
as a possible mechanism for vertical transport of Zn-65 in
in the sea", Int. J. Oceanol. Limnol 1: 237-215.
Horne, R.A. (1969), Marine Chemistry, wiley-Interscience. N.Y. 568p.
Hyman, L. (1940), The Invertebrates, V.1. McGraw-Hill, N.Y. 726p.
Kuenzler, E.J. (1969a), "Elimination of I, Co, Fe, and Zn by
marine zooplankton", pp. 162-173 in D.J. Nelson and F.C.
Evans, (ed.), Symposium on Radioecology. photocopy
324
reproduced by Atomic Energy Commission. 774p.
(1969b), "Elimination and transport of Co by
marine zooplankton," pp. 483-492. ibid.
Marion, R. (1971), "Assimilation and transfer of DDT residues
in a hydroid-nudibranch-tetribranch food chain) (Unpublished
MS on file at Hopkins Marine Station Library).
Marshall, S.M. and A.P. Orr, (1955), The Biology of a Copepod,
"Calanus finmarchicus". Oliver and Boyd, Edinburgh. 188p.
Martin, J.H., (1970), "The possible transport of trace metals
via moulted copepod exoskeletons", Limnol Oceanog. 15: 756-761.
Mauchline, J. and W.L. Templeton, (1964), "Artificial and
natural radioisotopes in the marine environment", Oceanog.
and Mar, Bio. A. Rev. 2: 229.
Osterberg, C.L., A.G. Carey, Jr., and H. Curl, (1963), "Acceler-
ation of sinking rates of radionuclides in the ocean", Nature
200: 1276-77.
Patterson, C.C., (1970), "Lead", in D. Long, ed., Impingement of
Man on the Ocean. preprint.
—-------------, (1965), "Contaminated and natural lead
environments of man", Arch. Env. Health 11: 311-360.
Riley, G.A., (1963), "Organic aggregates in sea water and the
dynamics of their formation and utilization", Limnol.
Oceanog. 8: 369-381
Riley, G.A., P.G. Wangersky, D.V. Hemert, (1964), "Organic
aggregates in tropical and subtropical surface waters of
the North Atlantic Ocean", Limnol. Oceanog. 9: 546-50.
Siegel, A., and B. Burke, (1965), "Sorption studies of cations
on 'bubble-produced organic aggregates' in sea water".
Deep-Sea Res. 12: 789-796.
State of California, Air Resources Board, (March, 1967), Lead
in the Environment and its Effect on Humans. 81 p.
Tatsumoto, M., and C.C. Patterson, (1963), "The concentration
of common lead in sea water", pp. 71-89 in J. Geiss and
E.D. Goldberg, ed., Earth Science and Meteoritics. North
Wellander, P., (1961), "Coupling between sea and air", pp. 4O1-
110 in M. Sears, ed., Oceanography, Horn-Shafer, Baltimore.
654 p.
Wilson, A.T., (1959), "Surface of the ocean as a source of air¬
borne nitrogenous materials and other plant nutrients",
Nature 184: 99-100.
C
Table 1-- Mean values obtained for Ag, Zn, Cu, Cr, Mn, Cd.
and Pb concentration in samples collected during five tows
in Monterey Bay. The standard error was computed as follows;
SE -
N-1
32
8



S
10

14 -
++ 40 44 4.
1+
.9.
.O
. —
.O
O
O
4
14R
+ —
+
+
4
—.
N-
N-
o

50
o


+
+
+
—
.

ORE

• O
V
8

+0
+ +
+
+6 40
1+0
10

a

N
o
O
OO
+ —
4.
++
+N
+ +0


.
.0
O

CE
+ +
+:
+ N +N
—
— —
.J
.

SO
OO
Do

O
+ + 1
+ +
+




*




3
O
2


0
o
.
6P

86 6
0
85
28
OS
g
o
0
12
3
R
1+4
+
1+
0
4N
+.

•
.O
.0
5
O


400 4
+N
+
140
+N
e
8
+
E
L
N
8
+
+N + +

+

.

O
8
* O
• O

O

NO
55
O
++
R
++
+N +
40
+0 +
40
4
9e
+.
0
+e
in



O
O
O


OO
+O +0
++
+0
+140
40 +0


H
— —
-
NO
.
O
• O
OE
0
+ 140
40 +
+0 1
40 +
ON


5
—0


A

• O

O
O
0
4  40 +
4 4
+N
+0
+0
—
i


OO
OO

o
5
5
00
320
N



00
+ +
4

ON
28
+O
+ N
ES
40 +

+.
O.

P
10 +
+ .
O
O

+0
45
—0
—0
++0
5
—0
•
+ N +
o

. O
0
O
Table #2 - The probability that the two populations compared
are from the same general population, as computed
by the
"t" test, ie. t =X:
- 22

65

11 n-1
33
O
Tabl
Populations
compared
Nueston copepods
vs.
Plankton copepods
Nueston E. pacifica
Plankton E. pacifica
Nueston P. bachii
vs.
Plankton P. bachii
Plankton inshore
opepods
vs.
Plankton offshore
opepods
33,
Cr
Ag Zn
Cu Mn
Cd Pb
.20 .20 .10 .60 .40 .10 .20
.80 .70 .30 .80 .20 .80 .05
.80 .90 .60 .80 .50 .50 .30
.10
.O1
.30
.80
.70
.30
90
O
e
0
0
Table III-- Comparison of concentrations of Cu, Mn, Zn.
and Pb between results of this study and those reported
by Martin (1970).
33.
O
Table III
this study
a) all copepods
n = 22
b) neuston copepods
n = 11
c) plankton copepods
n = 11
Martin (1970)
a) surface copepods
n = 10
b) all copepods
n = 22
Szabo (1968) copepods
Cu
19.71
t5.26
23.29
+ 10.30
16.12
+ 3.67
38
11
30
Mn
7.91
+ 1.21
6.64
+1.63
9.19
+ 1.77
23
29
11
Zn
+ 11
315
+ 74
191
+ 16
220
130
266
Pb
18.18
+ 8.96
29.96
-17.51
6.19
+ 1.39
39
19
——
35
0
C
Figure
Fl - Species composition and towing conditions for
the 11 runs in Monterey Bay. Abundance scale
is: +++ most abundant; ++ frequently observed;
+ seldom observed. Circles indicate sewer
effluents; corresponding numbers show treatment
(ie. primary, secondary, etc.).
33
33
San Lorenzo
FIGURE 1
River
SANTA CRUZ


Q
Tow l-3 runs
/7
1./29
15-0915
Calm-overcast
alnoid oeos ++
p. bachii
Tow 2-1 run
ocoo-C830
5/6
Overcast,cold,wind
Plankton: (10-15 M)
euston: Calanoid opepods +
Calnid oepod ++
achi++
surface)
+++
bachi
val shrimp ++
a
rval shrimp ++
Ta:
larval crab (zoa) +
arval rab
Elkhorn
Leptomedusae +
Gammarid amphipod +
V
Beroe forskali
Slough
larval fish+
phausid+
3-3 runs
To
5/1
30-1030
alm,overast
Plankton: Galanoid copero
Clnd oepods +
Neus
" +++
p. bachi
+ +++
P. bac
rval crab (megalops)
amphapods +

ow -3 runs
Salinas River
7
5/11
o900-1300
atly loudy,choppy
Plankton:Calanoid copdpods +
ton:alanoid opepods ++
Hyperid amphapods +
Siphonophores +
ral fish
yperid amphapods +
Euphausid
P. bac!
i +
Tomopterus
runs

57
5/21/7
TOW2
o030-02
101/3
ny,choppy,cold
rons
ia +++
Meuston:
C. P
rval crab (megalops
sh (small)
MONTERE
Siphonophores +
6
Medusae +
Tow 15 (con);0600-0700
Calanid opepo
ndy,choppy,cold
ifia +
plankton:
Neuston: Calanoid copepods
p. bachii
(10 M)
crab larve (megalops)
Calanoid copopods
ica
oa
squid (juvenile)

hapods +

D7
lankton-10 M:
Carmel River
Calanoid copepods
J
iphonophores +
Medusae
. bachi
T0W 5
larval fish+
O
Figure +2 - Neuston copepod relative density vs. planktoi
copepod relative density for tows
9.O
-10.0
-11.0
O.O
FIGURE II
0 —TOW
-TOW 2
X -TOW 4
8.O
-7.0
log plankton density (g/m-
33
O
Figure III a-- Graph of log relative density vs. log
concentration of Pb and Zn in calanoid copepod samples
collected at the surface.
Figure III b-- Graph of log relative density vs. log
concentration of Od in plankton copepod samples and in
neuston copepod samples.
C
6.0
5.O
4.0
3.0
2.0
-11.0
FIGURE IIa
Zn— Neuston
° Pb— Neuston

—10.0
—9.0
log density (g/m3)
—
2.0
1.5
1.0
11.0
10.0
7.0
9.O
8.0
log density (g/m3)
FIGURE Tb
Cd
o- Plankton
•-Neuston
00 0
340