Metals in Dipterans and Amphipods, 1.
ABSTRACT
Beach dipterans and amphipods were analyzed for heavy
metal levels using atomic absorption spectroscopy.
Flies showed higher concentrations of all major metals.
Very high levels of cadmium were noted in both beach
animals. An increase in metal level with age was
evident in the dipterans. Concentrations of iron,
zinc, copper, and lead were found to fluctuate sig-
nificantly with time.
Metals in Dipterans and Amphipods, 2.
INTRODUCTION
The study of major elements in plant and animal tissue dates
back to antiquity (Pliny, Celsus), and by the middle of the
eighteenth century a true trace element, lead, had been de
tected in animals (Henkel, 1755). Recent advances in organic
chemistry and analytical techniques have enabled precise es-
timates of trace metals in diverse organisms (Vinogradov, 1953;
Goldberg, 1966). As late as 1953, however, none of the 750,000
known species of insects had been tested for trace element
composition, and only 100 out of 15,500 species of crustaceans
had been analysed (Vinogradov, 1953). Although more recent
studies have begun to fill the vacuum in this area (Spector,
1956; Stamm, 1958; Warnick and Bell, 1969), no work to date
has focused on metal levels in arthropods of the sandy beach.
Over a seven week period, I attempted to determine trace ele-
ment levels in a marine and a terrestrial arthropod inhabiting
the beach. I was especially interested in the general question
of how a primarily marine and a land animal would compare in
metal levels, as well as in how concentrations would vary
geographically, temporally, and with age. Beach hoppers
amphipods of the genus Orchestoidea - and marine flies were
selected for comparison because they are known to exploit the
same food source, the beach wrack. I hoped to set a base line
with which future analyses could be compared in a temporal
study of pollution, as well as to establish reasonable ranges
of daily fluctuation for each metal.
Metals in Dipterans and A
lipods,
MATERIALS AND METHODS
Beach hoppers were collected at four points on the Monterey
Peninsula (figure 1): Orchestoidea corniculata from two
pocket beaches adjoining Hopkins Marine Station; O. calif-
orniana from Del Monte beach at the Monterey sewage outfall
and from the southern end of Carmel beach. Hoppers were
found by digging in the sand with a shovel or by lifting
segments of wrack. In the former case, the sand was combed by
hand and no hoppers which had been contacted by the metal
shovel were collected. Flies of the species Coelopa van-
duzeei and Fucellia rufitibia were caught at the same sites
A butterfly net was used to trap the flies as they swarmed
above the wrack. In addition, larvae of the coelopid fly
were collected from Carmel and lady bugs from Del Monte
beach. These were taken by hand directly from the wrack
and underlying sand. Sterile flasks were used in all cases
to transport the animals from the collection sites to the
laboratory.
Beach hoppers were retained in collection flasks for 24 hours,
after which they were frozen, washed in distilled water to
remove sand and paracitic mites, and dried at 60° for one
day. The same procedure was followed for the fly larvae and
lady bugs. Fly specimens were Killed immediately, however,
with ethyl acetate in a clean killing jar. They were then sorted
by species, washed, and dried. Triplicate samples were col-
lected when possible.
Dried samples were ground to a fine powder and approximately
gram or half-gram aliquots were digested. Ten ml of 90% nitric
acid were added to each sample, which was allowed to reflux
for at least one hour or until clear. The solutions were
then simmered down to 5 ml, cooled, and treated with hydrogen
Metals in Dipterans and Amphipods, 4.
peroxide until visible oxidation ceased. One ml of hydro-
chloric acid was added, and the samples were diluted to 25
ml with distilled water. A blank containing the reagents
and water was prepared as a control in each digestion.
Analysis for silver, cadmium, copper, iron, manganese, nickel,
lead, and zinc was carried out on a Perkin-Elmer atomic absorp-
tion spectrophotometer model 303. Laboratory standards were
run along with each series of tests to calibrate the absorp
tion scale. As there was no correction for background noise,
values up to 2% absorption were discarded due to possible
inaccuracy. A sample of ethyl acetate was analyzed as a
control for fly specimens. It proved to have no trace metals
of detectable amounts.
RESULTS AND DISCUSSION
Zinc, Iron, Copper and Cadmium: Beach flies showed consis-
tently higher levels of Zn, Fe, Cu and Cd than did amphipods
(figure 2). For the first tiwoe metals this relationship is
anticipated by former research on insects and crustacea
(Bowen, 1966). Unusually high concentrations (up to 240.0
ppm) of iron on the Hopkins Marine Station back beach may be
related to scrap metal from the Monterey Boat Works. Large
pieces of rusting iron are buried in the sand from surface
level to two feet in depth. These are covered by water at
high tide. Runoff from Cannery Row's remaining industries and
restaurants may also circulate metals to this beach. In
addition, erosion of the adjacent loosely-packed soil and
air-borne dust could contribute iron to this beach. Elevated
iron levels (as high as 298.1 ppm) near the Monterey outfall
seem not to be due to especially high metal levels on the
Metals in Dipterans and Amphipods, 5.
beach itself (Koski, 1972), and may reflect iron-rich wrack,
Copper is important as a respiratory pigment in arthropod
blood, and Bowen (1966) suggests that flies and amphipods
contain an equal amount of this metal, 50 ppm. My results
fall short of this figure except at Hopkins back beach where
copper may enter the ecosystem from boat paint intended to
leak the element to discourage fouling by marine animals.
Zinc, iron and copper are all essential to living organisms
as constituents of metalloenzymes and proteins.
Cadmium levels reported by Bowen (1966) indicate too little
of the metal for detection in insects and only 0.15 ppm in
crustacea. Warnick and Bell (1969) found that cadmium was
acutely toxic to fresh water insects in concentrations of
0.016 to 0.064 ppm. In light of these figures, the beach
arthropods showed very high (up to 149.7) levels of this
metal, suggesting a local source of contamination. Lady
bugs, which are predaceous terrestrial insects and swarm the
beaches following hibernation (Borror, 1964), contained no
detectable cadmium. This indicates that the metal's input
may be largely marine despite its low (0.05 microgram/liter)
level in "normal" sea water (Riley and Chester, 1971). Pro
teins containing cadmium have been found in several animals
(Vinogradov, 1953; Kagi and Vallee, 1961), but the metal is
considered toxic due to its ability to replace zinc in en-
zymes. Nilsson (1970) has compiled a list of the 20 known
toxic effects of cadmium, demonstrating that the metal is a
very wide-spectrum toxin.
Manganese: Manganese was low in all beach arthropods tested
(less than 10 ppm). Flies were slightly higher than hoppers at
each site, but not to the extent reported by Bowen (1966) -
a five-to-one ratio. The lady bugs had higher Mn content
(24.8 ppm) than the beach dwellers. This may be due to very
high concentrations in land plants - up to 630 ppm (Bertrand
and Silberstein, 1954) - or to accumulation in the gut walls
Metals in Dipterans and Amphipods, 6.
(Bowen, 1950). High levels of this metal are moderately
toxic, but the element is essential in trace amounts for
activating enzymes and as a protein constituent.
Lead, Nickel and Silver: Lead, nickel and silver occur in
truly trace amounts in hoppers and flies. The recorded
levels are subject to inaccuracy because of background
noise and difficulty in chart reading. Despite these limit-
ations, it is clear that amphipods concentrate more lead
than do the beach insects. This may reflect the 'mineral
armor" of calcium salts that cover the crustaceans since
lead accumulates in calcareous tissue. The hoppers' lead
level is up to thirty times the amount found in crustacea
from Bowen's (1966) summary, indicating possible local pol-
lution. As yet, no biological function is known for lead.
It is a cumulative poison in animals as it may inhibit
protein and gene synthesis, cellular oxidations, and other
essential functions (Underwood, 1971).
Both silver and nickel, which may be highly toxic in large
amounts, are barely detectable in beach hoppers and flies
with the techniques of analysis I employed. Because they
are so scarce, it is impossible to define any major trends
or comparisons in insects and amphipods.
Higher trace element levels in flies than in beach amphipods
may have several causes. From my own observations in the
field and lab and those of Remmert (1964), it is clear that
both hoppers and flies prefer the same food - brown algae
(in Monterey, Macrocystis pyrifera). Secondary foods of the
two animals differ, however. Flies are attracted to car-
rion and may eat bacteria off the wrack rather than the sea-
weed itself. Borror (1964) states that coelopid flies feed
on flowers near the beach, although I did not find any evi-
dence of this practice at my test sites. The Orchestoidea
species will eat the dead of their own populations but pre-
Metals in Dipterans and Amphipods, 7.
fer cardboard and chewable trash to the bodies of fish and
birds (Bowers, 1964). In addition, the animals' habitats
vary. Hoppers constitute a stable and non-migratory pop-
ulation on the beach. They burrow in the sand during the
day, occasionallyhbeing covered by a high tide, and search
for food in a local area at night. The ecology of marine
flies is not as clearly understood, but it is obvious that
these insects have a wider range of movement than the amphipods.
Flies invade a beach following the deposition of wrack and may
live inside the rotting seaweed or in dry holdfasts. Their
stay is temporary, and Cole (1965) believes that Coelopa
may have migratory flights. Whether the flies exploit ter
restrial food sources during some period of their lives is
not known. A final reason why metal levels may be higher
in flies than in beach hoppers is a biochemical one. Under-
wood (1971) reminds us that knowing the concentration of a
metal is not meaningful unless its interaction with other
elements is also understood. The insect's absorption of
metals through the intestine and tracheole wall (Goodwin,
1965) may exceed that of the amphipod. Metabolic pathways
could also be sufficiently different in the two animals to
cause consistent variations in metal levels.
A comparison of larval and adult coelopid flies and of old
and young beach hoppers is shown in figure 3. Lower metal
levels in the larvae for all elements but Mn may be due to
their shorter lives, less varied diets (they are physically
limited to the decaying kelp in which they are scavengers,
while the adults range over the entire beach), or juvenile
set of enzymes and hormones. Bowen (1950) found that Mn
accumulated in juvenile wasps until pupation, at which time
levels dropped.. His finding may apply as well to the dipterans
I tested. In contrast, the adult and juvenile hoppers were
very similar in trace metal levels. This is probably because
the two age groups share a habitat, food source, and metabolic
complement.
Metals in Dipterans and Amphipods, 8.
Variation in trace element levels onoone beach would be
expected over time due to chance importation of actual metal
or metal-rich food, terrestrial rumoff, rainfall, etc. The
results of a day-to-day study of the Hopkins back beach
hopper, 0. corniculata, are summarized in figure 4. Iron
was found to fluctuate dramatically over the time period
tested (variations up to 200 ppm). This may represent var-
iations in leaching caused by high tides covering the beach's
scrap iron, changes in food source, orrdust contamination.
Copper, lead and zinc fluctuated moderately over time, while
cadmium, manganese, nickel, and silver showed stable levels.
Each metal varied independently. The range of fluctuation
in Fe, Zn, Cu, and Pb is significant enough to justify studies
over time rather than single day sampling for these metals
on a particular beach. The results throw doubt on data from
single collections, especially in pollution studies.
Variation in metal levels due to species differences was
studied for the beach flies, Coelopa vanduzeei and Fucellia
rufitibia, re collected from the same wrack beds. Over the
Monterey Peninsula, no significant difference in elementary
composition was noted. A comparison between the two beach
hopper species was not possible because the animals did not
occur sympatrically in any of my collection sites.
It is of interest that the beach "visitors" - the flies-
showed higher levels of all major metals than the stationary
amphipods. Elevated cadmium levels are particularly un-
expected and suggest that contamination of a possibly mar-
ine origin has more impact of the terrestrial ecosystem
than was previously suspected. Metal analyses of other
terrestrial animals that find food on the beach would be
an important follow-up to this study. No fewer than seven
species of birds, only two of which are considered shore
dwellers, have been observed to eat fly larvae from the
beach wrack (Baldridge, 1972). Glynn's stomach analyses of
Metals in Dipterans and Amphipods, 9.
black turnstones and gulls in 1965 showed that both of these
scavengers consume intertidal insects. In addition, an at-
tempt to track down the source of cadmium pollution in Mon-
terey Bay and to determine the metal's physiological effect
on local dipterans and amphipods would be of interest.
ACKNOWLEDGMENT
My thanks to Dr. John Martin for his theoretical and
technical advice.
Metals in Dipterans and Amphipods, 10.
FIGURE CAPTIONS
Collection sites on the Monterey Peninsula.
Figure 1:
A. Del Monte beach
B. Hopkins Marine Station back beach
C. Hopkins Marine Station front beach
D.
Carmel beach
Metal levels in ppm dry weight for dipterans
Figure 2:
and amphipods at four locations; "nd" indic-
ates that metal was not detectable.
Comparison of metal levels in juveniles and
Figure 3:
adults.by ppm dry weight. Flies and larvae
from Carmel; hoppers from Hopkins back beach.
Variation in metal concentration (ppm dry
Figure 4:
weight) with time. Continuous slope between
sampling points does not imply constant levels.
Metals in Dipterans and Amphipods, 11
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Row
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FIGURE 1
Metals in Dipterans and Amphipods, 12.
Os0
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Site
FIGURE 2
Amphipod
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Metals in Dipterans and Amphipods, 13.
FIGURE 3
Metals in Dipterans and Amphipods, 14.
FIGURE 4
Metals in Dipterans and Amphipods, 15.
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