INTRODUCTION
Studies on nitrogenous excretion in crustaceans have shown this
group to be principally ammonotelic, excretiag from 40 to 85% of their
total nitrogen as ammonia (Parry, 1960). However, most of the
species examined have been decapods and virtually nothing is known
of exretion in barnacles. This study was designed to determine the
kinds and amounts of nitrogenous excretory products in the barnacle,
Balanus nubilus. This species was chosen because of its large size
and because large quantities of mantle cavity fluid containing excretory
products could easily be obtained without injury to the animal.
MATERIALS AND METHODS
The specimens used measured from 4 to 8.5 cm. in basal shell dia-
meter and were collected from the pilings at Fisherman's Wharf in Mon-
terey, California. They were scraped free of adherent debris and
commensal organisms and were placed in running seawater in the labora-
tory. Prior to collection of fluid for analysis, the animals were re-
moved from their tanks, blotted, and allowed to stand for 4 hours.
Fluid was drained by inverting the animals over a beaker; an average
of 2 ml. per barnacle was obtained in this manner. The fluid was pooled
and deprotinized with 10% Na Tungstate and 2/3 N Sulfuric Acid according
to Haden's modification of the method of Folin and Mu (1923).
lotal nitrogen, ammonia nitrogen, and urea nitrogen were determined
by the microdiffusion technique of Ternberg (1965). Total nitrogen was
determined with a 1 ml. sample after digestion with concentrated
sulfuric acid saturated with cupric sulfate. These samples were diluted
with 0.6 ml. of distilled water and 4 ml. of 10N sodium hydroxide were
added in contrast to the saturated sodium carbonate proscribed in Tern-
bergs original method.
Urea was assayed after conversion to ammonium carbonate by a 15 min.
incubation with 0.1 ml. of a 50 mg.?ml. soln of urease and distilled
water (urease obtained from Matheson, Coleman, and Bell).
Uric acid was determined using the colorimetric method of Sobrin-
ho- Simöes (1965).
The microdiffusion tecnique was found to be reproducible within
10.22 ug of nitrogen. The digestion procedure for total nitrogen,
however, was reproducible only within + 1.5 ug of nitrogen.
RESULTS
Balanus nubilus was found to excrete ammonia and uric acid (see
lable 1), but no urea was detected. The uric acid was in very high rela-
tive concentrations, averaging 80% of the total nitrogen from composite
tests (uric acid N - 3.3 1.9 ug/ml., NHg N - 0.89 + .12 ug/ml.). How-
ever when the total nitrogen was assayed for by digestion, the quan-
tity was invariably lower than the sum of the composite tests (3.5 +
1.5 ug/ml. as compared to 4.1 + 1.7 ug/ml.). The assays on body fluid
gave the same results, but in higher concentrations. Statistically,
the ranges for the total nitrogen assay and the composite assays are com¬
patible, but the spotty reproduciblity of the digestion procedure still
reduces the confidence in the extreme accuracy of the results.
DISCUSSION
The lack of agreement between the composite nitrogen values
and those obtained by digestion suggests that the predominant ex-
cretory product is not identical to uric acid. The low amounts of
excretory products present in the fluid will regire considerable
concentration of the fluids before the nature of the products can be
determined with certainty.
If we can assume that uric acid is indeed the principle nitrogenous
excretory product in Balanus nubilus, then we can ask the question
why. Possible the gross anatomy of the animal offers a clus. Essential-
ly, the barnacle is housed in its shell with limited access to the out-
side. In periods of low tide, when the animal is exposed, it would
be advantageous to excrete the insoluble uric acid rather than the
toxic and soluble ammonia or urea. This is possible, but no especially
meaningful since Palanus nubilus is usually not exposed for over
oe
six hours, and the low concentrations found a four hours of incubation
would not seem to be toxic.
SUMMARY
Studies on the nitrogenous excretory products of Balanus nubilus
indicate that the barnacle excretes a large part of the total nitrogen
in the form of a uric acid-like material.
TABLE 1
(quantities in ug N/ml. of mantle cavity fluid)
Total N NHBN
Ures N Uric acidN
0 44.9
Body Fluid
46.2
2.9
0 2.34 8
Mantle cavity
3. 51 1.5 0.94. 12
fluid
Ranges
1. For total nitrogen assay: 2.0 - 5.0
2. For ctotalite nitrogen,acemposite assays: 3.2 - 5.2
14
LITERATURE CITED
Haden, R.L. 1923. A modification of the Folin-Wu method for
making protein-free blood filtrates. J.Biol.Chem. 56: 469-471.
Parry, Gwyneth. 1960. Excretion" in The Physiology of Crustacea,
edit. by Talbot H. Waterman. p. 341. Academic Press, New York and
London.
Sobrinhos-Simoes M. 1965. A sensitive method for measurement of
serum uric acid using hydroxyl amine. J. Lab. and Clin. Med. 65(4):
665-668.
Ternberg J.L. and Hershey, F.B. 1964. Colorimetrec determination of
blood ammonia. J. Lab & Clin. Med. 56: 766 -776.