COMPOSITION
PELLETS
AND NUTRITIVE
VALUE OF FECAL
OF A MARINE CRUSTACEAN1
R. E. Johannes’ and Masako SatomP
University
of Georgia
Marinc
Institute,
Sapclo Island,
Georgia
ABSTRACI’
The role of feces in energy flow and nutrient
cycles in the marine ccosystcm was
examined using fecal pellets of the shrimp Palaemonetes pugio, fed on the diatom N&zschia
The pellets were rich in organic matter, particularly
protein.
The feces were
closterium.
readily eaten by P. pu& when diatoms were not available
and assimilation
efficiency
was high, indicating
that the pellets contained
considerable
assimilable
organic matter.
Solution and bacterial respiration
rcduccd the organic content of the feces while light and
dissolved organic matter stimulated
the growth of autotrophic
and heterotrophic
microorganisms.
It is estimated that the rate of incorporation
of organic matter into fecal pellets in the
sea exceeds the rate of incorporation
of organic matter into herbivore tissue and that fecal
pellets therefore constitute a major potential food source for marine animals.
INTRODUCTION
The possible importance of fecal pellets
as food for marinc animals has occurred
to numerous workers (e.g., Harvey et al.
1935; Zcnkevich and Birstcin 1956; Marshall and Orr 1955; Cushing 1959; Jorgensen 1962; Beklemishev
1962). Newell’s
( 1965) recent demonstration that the marinc gastropod Hydrobia &a,
a deposit
feeder, will ingest and partially assimilate
its own feces appears to bc the only publishcd information other than a few anccdotal accounts of marinc
coprophagy
(e.g., Zcnkevich and Birstein 1956; Harvcy 1955).
In the prcscnt paper, the nutritive value
of fecal pellets of an omnivorous marine
crustacean fed on diatoms and the chcmical changes occurring
in these pellets
when held under a variety of cnvironmental conditions arc repo’rted. The significance of fecal pellets in energy flow and
nutrient cycling in marinc ecosystems is
discussed.
1 National Science l?oundation
Grants GB 1040
and G-19368 and grants from the Sapclo Island
Research Foundation
supported this work.
Contribution
No. 106 from the University
of Georgia
Marine Institute.
address : Department
of Zoology,
2 Present
Univ. of Georgia, Athens
30601.
Laboratory
of Phycology,
3 Present address:
Tokyo
Univ.
of Fisheries,
Konan,
Minato-ku,
Japan.
It is a pleasure to acknowlcdgc the cxccllent technical assistance of Mrs. Sandra
Linton. We also wish to thank Drs. K. L.
Webb, L. R. Pomeroy, and E:. P. Odum,
who read and criticized the manuscript.
Professor E. J. Fcrguson Wood identified
the diatom.
METHODS
AND
MATEXIALS
Adult Palaemonetes pugio, 2.2-2.5 cm
long from eye to tip of tclson, were collectcd from tidal creeks at Sapelo Island,
Georgia. Attempts in the field to, collect
sufficient fecal material from these animals for experimental purposes were unsuccessful. Animals fed in the laboratory
proved to be a satisfactory source of fecal
material.
Cultures of the diatom, Nitzschia closterium, were grown for food in
12-inch (30.5 cm) diameter glass-covered
finger bowls in seawater enriched with
modified Miqucl’s solution ( Allen 1914 ) ,
The cultures were grown at 26 * 1C in
a chamber illuminated
with white fluorescent lamps.
About 15 P, pugio with empty guts
were placed in each of several N. closterium cultures 6-8 days old and still in the
exponential
growth phase. To facilitate
ingestion, we rubbed off films of diatoms
growing on the surface of the culture
dishes and broke them into fragments con191
192
R. E.
JOIIANNES
AND
taining several thousand diatoms, As they
were voided, we collected fecal pellets
with a fine-tipped eye dropper, About 1
mg (dry wt) of fecal material was collected
and transfcrrcd briefly to distilled water
to rinse off adhering salt. (Microscopic
examination provided no evidence to suggest that the resulting
momentary
decrease in osmotic concentration
outside
fecal microorganisms caused them to rupture and release their contents into the
water.)
The samples were then immediately transferred to an acid-washed, tared
glass filter about 25-mm square, ovendried overnight, and weighed,
Replicate
samples, usually three or more, were
taken for each chemical analysis.
An experiment was run in triplicate to
determine the organic carbon assimilation efficiency
of N. closterium by P.
pugio. Diatom cultures were divided into
equal portions by pouring them into a
filter funnel containing a two-holed rubber stopper with two rubber tubes leading into separate beakers and adjusted
with screw clamps to deliver equal volumes. The diatom film fragments were
removed from one beaker with an eye
dropper, rinsed in distilled water, placed
on a tared glass filter, dried, weighed,
and analyzed for organic carbon.
P. pugio in the duplicate cultures were
fed diatoms ad Zibitum for 3 hr. The
shrimp had been held without food for 12
hr prior to the experiment.
Fecal pellets
were removed periodically
and uneaten
diatom film, fragments were removed at
the .end of the experiment. After feeding,
the animals were held in filtered seawater
for 30 min (the approximate time it takes
food to pass through the gut), and the
feces produced during this time were also
collected, Fecal pellets and uneaten diatoms were separately dried and weighed
and the fecal pellets analyzed for organic
carbon. Percentage assimilation efficiencies of organic carbon were measured as:
[ (organic carbon eaten - organic carbon
released in fcces)/organic carbon eaten] X
100.
Organic carbon content was measured
MASAKO
SATOMI
as total oxidizable
material
using the
chromic acid digestion method of Fox,
Isaacs, and Corcoran (1952) as modified
by Menzel and Ryther ( 1964).
Total carbohydrate
was measured by
the phenol method of Dubois et al. (1956)
as described by Marshall and Orr ( 1962).
Lipid was measured by the method o,f
Mukerjee ( 1956) as adapted by Strickland and Parsons ( 1960).
Total protein was determined from the
Kjeldahl nitrogen (N x 6.25 = protein) estimated by Law and Co., Atlanta, Georgia.
Total phosphorus
was measured by
mineralizing
samples with perchloric acid
as described by Strickland and Parsons
( 1960) and measuring dissolved inorganic
phosphate by the one-solution method of
Murphy and Riley (1962) as described by
Strickland ( unpublished manuscript ) .
Dry weights and ash weights were determined after heating the samples overnight at 82C and 5OOC, respectively.
fluorescence
microscopy
Blue
light
(Wood 1962) was used to examine the
distribution of chlorophyll or phaeophytin
or both in fecal pellets.
RESULTS
Visual description of fecal pellets
P. pugio feces were released in rodshaped pellets 50-200 p wide and 1 mm
to 2 cm long. The pellets were covered
with a thin transparent pellicle similar to
those surrounding fecal pellets of various
other aquatic crustaceans (Forster 1953;
Gauld 1957; Reeve 1963).
The feces were a brownish orange color
similar to that of the experimental food.
The bulk of the pigment was not in diatoms but in thin, wrinkled films or clumps
distributed irregularly throughout the pellet. Over 99% of the voided diatom frustules were empty, though unbroken. Less
than 1% of the diatoms were thus undigested, but these were readily visible
microscopy
owing to
using fluorescent
their bright fluorescence. Feces examined
immediately
after voiding were densely
packed with bacteria. These cells were of
intestinal origin because there were few
bacteria among the ingested diatoms.
COMPOSITION
AND
NUTRITIVE
VALUE
OF
FECAL
PELLETS
193
1. Chemical composition of fecal pellets
ingested material occurred as it passed
of P. pugio fed on N. closterium and fed on feces through the gut and that this reduction
TABLE
-_-;
-
Constituent
(“/o dry weight)*
7.
organic carbon
protein (N x 6.25)
carbohydrate
lipid
phosphorus
ash
-~____~
c__.-
20 (24)
28 (3)
13 (3)
2.5 (2)
1.7 (5)
26 (5)
~--~-_ -_
~.
Fecal x2llcts
dcrivc A from
ingested feces
Fecal pc11ets
&rived from
ingcstcd diatoms
12
14
(3)
(3)
0.9 (3)
-_
* Numbers in parentheses are the number
on which adjacent value is based.
--
--
-
of analyses
After a week in the light, fecal pellets
were no longer recognizable as such. The
feces were in amorphous,
translucent
fragments containing numerous bacteria.
The outer membranes had disappeared.
Colorless microflagellates
( 24 ,U diam )
adhered to or moved around in the vicinity of the outer surface. Empty diatom
frustules were still visible and living diatoms were growing in and on the fragments.
Chemical
composition,
food value
Organic carbon assimilation efficiencies
of 78, 78, and 79% were measured in triplicate experiments with P. pugio fed on
N. closterium. The feces weighed an average of 35% as much as the food from
which they were derived.
Their initial
chemical composition is shown in Table
1. Approximately
20% of the fecal material was organic carbon, with protein
predominating
among the organic components.
When living diatoms were not available, P. pugio reingested their own feces.
Analyses
of the resulting
“doubly-digested” feces (Table 1) showed a reduction in organic
carbon, protein,
and
phosphorus contents of 40, 50, and 44%,
respectively.
Owing to the small quantities of material involved, the decrease in weight attending the digestion of feces was not
measured. Considerably
less fecal matcrial appeared to be voided than was ingcstcd. It is assumed that when feces
were eaten a reduction in weight of the
was comparable to the decrease in weight
of ingested diatoms as they passed through
the gut, If this is correct, the measured
percentage decrease per unit weight of
any fecal constituent
was considerably
less than the actual percentage of this
substance removed during digestion. For
example, when 1.0 mg of feces containing
28% pro,tcin arc eaten and result in the
production of 0.35 mg of feces containing
14% protein, the percentage decrease in
protein content is 50%, but the quantity
of protein actually removed from the food
( = assimilation efficiency) would be
(1 x 0.28) - (0.35 x 0.14) x Loo _ 82”/
0.
1 x 0.28
“Doubly-digested”
feces were not initially re-eaten by P. pugio. Several days
after release, during which time the pellets were held in the light, the fecal material was once again eaten. During the
following
weeks, fecal material was reingested several more times.
Several species of local benthic animals
known or believed to feed on detritus
were held in aquaria and P. pugio fecal
pcllcts were introduced.
Species ingesting
feces were the telcost Fundulus heteroclitus, the gastropod Na.ssa obsoleta, and the
crustaceans Uca pugnax and Pagurus longicarpus.
Alteration of chemical composition
under various environmental
conditions
The effects of bacterial action, autolysis,
solution, light, and dissolved organic matter on the chemical composition of fecal
pellets were examined to dctcrmine what
chemical changes feces may undergo after
being released.
In a series of 12-inch ( 3.5 cm) diam
finger bowls, 2-3 mg of fecal pellets were
held in 300 ml of HA Milliporc@ filtered
seawater. The seawater was taken from
400-ml N. closterium cultures in which 15
P. pugio had fed for 4 hr. The bowls
were placed in the dark and fecal pellet
R. E.
/
JOHANNES
AND
CARBOHYDRATE
MASAKO
SATOMI
FIG. 2. Effect of light on organic carbon content of fecal pellets.
(Each point is the mean of
three or more determinations.
)
LIPID
4
0
I
I
L
2
PHOSPHORUS
I
3
TIME
I
4
I
5
I
6
I
7
(DAYS1
1. Change in composition
of fecal pellets
held in the dark.
(Each point is the mean of
three or more determinations. )
FIG.
samples were taken for chemical analysis
periodically for four days.
Autolysis, solution, and bacterial respiration resulted in a decrease in percentages of all organic constituents measured
and a reciprocal increase in per cent ash
( Fig. 1). Any bacterial growth at the
expense of dissolved organic metabolites
in the water, resulting in the addition of
organic matter to the fecal pellets, was
masked by
concurrent
decomposition
processes of greater magnitude.
Reduction in protein was pronounced while the
content decreased slightly
carbohydrate
and the lipid content did not change significantly.
The phosphorus content decreased to
less than one-half its original concentration within two days. (A subsequent experiment not included in Fig. 1 showed
that the phosphorus content decreased by
one-third within 8 hr, suggesting an initial
rapid physical release of soluble phosphorus. )
To determine how much reduction in
organic content was due to loss of organic
substances via solution, as opposed to
bacterial respiration, analyses were made
on feces irradiated with ultraviolet
light
to kill bacteria. The feces were irradiated for 1 hr, the cultures were tightly
covered with flexible,
adhesive plastic
sheets ( Saran Wrap) and held in the dark
for four days. The feces were then analyzed Eor organic carbon. Tests for bacteria made by streaking the feces on
ZoBell’s 2216 medium were negative. The
organic content decreased by 13-24%
( duplicate experiments ) compared with a
decrease of 56-55% in unirradiated
culturcs.
Bowls of fecal pellets were held in the
culture chamber and sampled periodically
for seven days (Fig. 2) to determine what
effect light had on changes in organic
content of feces. The organic content decreased approximately half as fast in the
light as in the dark for the first three days.
An increase in organic content took place
during the next four days until feces possessed approximately the original organic
carbon content of fresh feces. This increase was due to the growth of diatoms
originating from the viable cells released
COMPOSITION
AND
NUTRITIVE
VALUE
OF
FECAL
PELLETS
195
converted to food by the time the intestinal contents were egestcd-about
30 min
after the original food was eaten. This
of intestinal
residues by
“reprocessing”
initial
concentration
of
dissolved
organic
bactebacteria
appears
to
bc
a
mechanism
for
100
0
10
rial nutrients
(mg/liter)
---____
-.reducing
entropy
within
marine
food
-5%
+23%
Changes in organic
A -55%
webs.
carbon in feces
In the prcscnt cxpcriments, “efficiency”
B
-50%
+14%
+25%
after four days
-___
in conversion of the organic matter in
* A and B are duplicate
experiments.
diatoms into fecal organic matter was
about 20%. These data, plus published
in the feces. Thcsc growing diatoms wcrc
studies of assimilation of phytoplankton
visible upon microscopic examination of by zooplankton summarized by Conover
the fcccs.
(1964L suggest that the average cffiTo determine whether dissolved organic
ciency of marine herbivores in converting
matter is assimilated by microorganisms in food to feces is somewhat in excess of
the feces, fecal pellets were held in the 20%. Published
information
on gross
dark in three bowls of artificial seawater
growth efficiencies of marine herbivore
containing 0, 10, and 100 mg/liter, respec- populations, that is, (calories of growth/
tively, of a dissolved organic nutrient mixcalories ingested) x 100, is scarce, but it
ture for marine bacteria (Johannes 1964).
is probably safe to say that the mean value
After four days, the fecal pellets were ana- is less than 20%, This means that the rate
lyzed for organic carbon ( Table 2). At of production
of organic matter in the
an initial concentration 0E 10 mg/liter, or- feces of marine herbivores probably exganic nutrients were incorporated into the ceeds the rate of production of organic
feces at a rate preventing any significant
matter in herbivore
tissue. Additional
decrease in fecal organic content due to smaller quantities of organic matter will
concurrent decomposition.
In a dissolved
also be incorporated into feces at higher
organic nutrient concentration of 100 mg/
trophic
levels.
Fecal pellets therefore
liter, fecal pellets increased significantly
constitute a large potential food source
in organic content.
for marine animals.
P. pugio is extremely abundant in tidal
DISCUSSION
creeks along the Georgia coast. Georgia
Fecal pellets produced by P. pugio fed coastal waters are charactcrizcd by much
detritus and many detritus feeders. Five
on N. closterium were rich in assimilable
protein. This might appear to indicate a of these species were tcstcd and observed
“waste” of food, but organic carbon assim- to feed on P. pugio feces in the laboratory.
ilation efficiency was about 78% and fecal It thus appears that P. pugio fecal pellets
organic matter was largely in the form of provide a source of food for a variety of
intestinal bacteria and not undigested dia- estuarine organisms, including P, pugio.
Newell (1965) reports that fecal pellets
toms. The results indicate that food resiintertidal
marine
dues are converted into assimilable bac- of the deposit-feeding
ulna and Macoma
teria in the posterior portion of the gut. molluscs, Hydrobia
bahhica, undergo chemical changes quite
[In the chitin-lined
crustacean hindgut,
unlike those observed in the present study.
bacterial activity is high and no digestion
Feces initially contained very lo,w protein
occurs (Zhukova 1963) .]
concentrations.
Growth of nonphotosynThe capacity of marine bacteria to functhctic microorganisms in the fcccs resulted
tion as waste converters (ZoBell and Feltin a marked incrcasc in protein content
ham 1938) is strikingly illustrated here;
over a period of three days. These micromost of the particulate
organic residues
obtained their niwere organisms apparently
arising from digestion in P. pugio
TABLE 2. Effect of clissolvecl organic matter
organic carbon content of fecal pellets held
the dark*
----_______---
on
in
196
R. E.
JOHANNES
AND
trogen from the overlying waters and their
energy from the nitrogen-poor
organic
compounds in the feces. The newly incorporated protein was largely assimilated
when H. ulwa ingested these pellets.
Zooplankton
arc the most productive
faunal element in the sea; the need for
some insight into the role of the feces of
these animals in nutrient cycles and energy flow in the plankton and the difficulty of obtaining
this information
directly (Corner 1961) justify an attempt
to extrapolate cautiously from present observations. Phytoplankton
densities have
often been reported to be inadequate to
meet the food requirements of zooplankton (see Jorgensen 1962; Raymont 1963;
Conover 1964). Hart ( 1942) and Harvey
et al. (1935) have observed large numbers of Iccal pellets accompanying
low
phytoplankton
crops. Planktonic euphausiids, copepods, mysids, and ostracods
have been reported to ingest fecal material (Zenkevich and Birstein 1956; Harvey
1955; Beklemishev
1962, and others ).
Present observations and those of Newell
(1965) indicate that feces contain assimilable organic matter owing to microbial
reconstitution
of the food residues from
which they originate. Considerations discussed above further suggest that feces
may be a quantitatively
significant source
of energy for marine animals, including
zooplankton.
If fecal pellets were to sink quantitatively out of the euphotic zone, this would
result in the rapid removal of large quantities of phosphorus from the upper waters. The present results suggest two
ways in which this loss is minimized:
1)
solution of fecal phosphorus and 2) ingestion of fecal pellets and assimilation of
phosphorus by zooplankton.
The present results suggest that in the
euphotic zone the growth of autotrophic
and heterotrophic
fecal microflora, facilitated by high light intensities and relatively high dissolved organic matter concentrations, will at least partially
offset
the loss of organic matter from fecal pellets due to solution and bacterial respira-
MASAKO
SATOMI
tion. A decrease in organic content will
occur once the pellets sink below the euphotic zone.
In summary, it appears that a significant fraction of the energy contained in
marine communities is channeled into the
production of feces. For ecological purposes it may be convenient to think of
fecal pellets as organisms; they consist in
part of aggregates of living cells, they
consume and release nutrients and organic
matter, and they serve as food for marinc
animals. “Populations” of fecal pellets are
thus a dynamic component of marine ecosystems, participating
in energy flow and
nutrient cycles in a quantitatively
significant way.
REFERENCES
ALLEN, E. J.
1914.
On the culture
of the
Thalassiosira
gravidu
planktonic
diatom,
seawater.
J. Marine
Cleve,
in artificial
Biol. Assoc. U.K., 10: 417-439.
BEKLEMISJIEV, C. W.
1962. Superfluous
fecdzooplankton.
ing
of marine
herbivorous
Rappt.
Proces-Verbaux
Reunions,
Conseil
Perm. Intern.
Exploration
Mcr, 153:
168113.
and nuCONOVER, R. J. 1964. Food relations
trition of zooplankton.
Narragansett
Marinc
Lab. Occasional Publ. 2, p. 81-91.
CORNER, E. D. S. 1961. On the nutrition
and
metabolism
of zooplankton.
I. Preliminary
observations
on the feeding of the marine
copepod Calanus he2golandicw
( Claus ) . J.
Marine Biol. Assoc. U.K., 41: 5-16.
1959. The seasonal variation
CUSHING, D. II.
in oceanic production
as a problem in popuJ. Conseil, Conseil Perm.
lation dynamics.
Intern. Exploration
Mer, 24: 455-464.
DUBOIS, M., K. A. GILLIES, J. K. HAMILTON, P.
A. REEBERS, AND F. SETH.
1956. Colorimetric
method
for the determination
of
sugars and related substances.
Anal. Chem.,
28: 350-356.
membranes
Fonsrnu,
G. R. 1953,. Peritrophic
in the Caridea
( Crustacea,
Decapoda ) . J.
Marine Biol. Assoc. U.K., 32: 315-318.
Fox, D. L., J, D. ISAACS, AND E. F. CORCORAN.
Marinc
leptotel,
its recovery,
mea1952.
sIu;ygn;and
distribution.
J. Marinc
Rcs.,
GATJLD,' D. T. 19157. A peritrophic
Nature,
in Calanoid copepods.
326.
Phytoplankton
1942.
HART, T. J.
in Antarctic
surface
waters.
Rept., 21: 263-348.
mcmbranc
179: 325periodicity
Discovery
COMPOSITION
AND
NUTFWIXVE
1955. The chemistry and ferHARVEY, H. W.
tility
of seawaters.
Cambridge,
London, *
England. 224 p.
-,
L. H. N. COOPEX, M. V. LE~OUR, AND
F. S. RUSSO.
1935. Plankton
production
and its control.
J. M arine Biol. Assoc. U.K.,
20: 407-441.
JOHANNES, R. E. 1964. Uptake and release of
dissolved
organic
phosphorus
by reprcsentatives of a coastal marine ecosystem.
Limnol. Oceanog., 9: 224-234.
JORGENSEN, C. B.
The food of filter
1962.
feeding
organisms.
Rappt.
Proces-Verbaux
Reunions, Conseil Perm. Intern. Exploration
Mcr, 153: 39-47.
MARSIIALL, S. N., AND A. P. Onn.
1955. Biology of a Marine Copepod.
Oliver & Boyd,
Edinburgh,
Scotland.
188 p.
-,
AND -,
1962. Carbohydrates
as
a measure
of phytoplankton.
J. Marine
Biol. Assoc. U.K., 42: 511-519:
MENZEL, D. W., AND J. II. RYTHEK 1964. The
composition
of particulate
organic
matter
in the western
North
Atlantic.
Limnol.
Occanog., 9: 179-186.
MUKIUXJEE,P. 1956. Use of ionic dyes in the
analysis of ionic surfactants
and other ionic
organic compounds.
Anal. Chem., 28: 870-
873.
MURPHY, J., AND J. P. RILEY.
ficd
single
solution
method
196% A modifor the dcter-
VALUE
OF
FECAL
PELLETS
197
mination
of phosphate
in natural
waters.
Anal. Chim. Acta, 27: 31-36.
NEWELL, B. 1965. The role of detritus in the
nutrition
of two marinc deposit feeders, the
Prosobranch
I-lydrohia
uZva and the bivalve
Macoma balthica.
Proc. Zool. Sot. London,
144 ( 1) : 25-45.
and proRAYMONT, J. E. G. 1963. Plankton
Macmillan,
New
ductivity
of the oceans.
York, N.Y. 660 p.
REEVE, M. R. 1963. The filter feeding of ArIII. Fecal pellets and their associtemia.
atcd mcmbrancs.
J. Exptl. Biol., 40: 215221.
STRICKLAND, J. D. H., AND T. R. PAILSONS.
1960. A manual of seawater analysis.
Bull.
Fishcrics Res. Board Can., 125: 185 p.
WOOD, E. J. F. 1962. A method for phytoLimnol.
Oceanog., 7: 32plankton
study.
35.
ZENKEVICII, L. A., AND J, A. BIRSTEIN. 1956.
Studies of the deep water fauna and related
problems.
Deep-Sea Rcs., 4: 54-64.
sigZIImoVA, A. I. 1963. On the quantitative
nificance
of microorganisms
in the nutrition
of aquatic invertebrates,
p. 699-710.
In C.
H. Oppenheimer
[ea.], Symposium
on maThomas, Springfield,
Ill.
rinc microbiology.
1938.
ZOBELL, C. II., AND C. B. FELTILW.
Bacteria as food for certain marinc invcrtebrates.
J. Marine Res., 1: 312-317.