A Mechanism of Color Variation Operating in the West Coast 
Sea Hare, Aplysia calijornica Cooper 
Lindsay R. Winkler^ 
The wide variation in the coloration of 
different specimens of Aplysia californica 
Cooper, which inhabits the algal zones from 
Monterey Bay on the central California coast 
to the Gulf of California, has been the source 
of considerable question as to the specific 
homogeneity of the species. Cockerell (1901) 
based a new species name, A. ritteri, on an 
especially brightly colored variety. Garstang 
(1890) experimented with the European 
Aplysia and showed that there was a definite 
connection between diet and coloration. He 
believed that the veliger larvae settled in deep 
water and then migrated from deep water 
through the red, brown, and green algal 
zones, taking in turn the color of each. 
MacMunn (1899) and Schreiber (1932) 
have indicated that the normal skin pigment 
is basically made up of degradation products 
of the tetrapyrrole molecule of chlorophyll. 
These are partly porphyrins, which are cyclic 
tetrapyrrole compounds, and bilins, which 
are linear chains of pyrrole molecules resulting 
from a break in the cyclic tetrapyrrole ring. 
The color and consequent absorption spec- 
trum of these products varies as their struc- 
ture is changed. Thus bilins from degraded 
green chlorophyll can produce a variety of 
blues, browns, greens, yellows, and reds 
which are all characteristic colors of the bilin 
compounds. 
^ Work done at Allan Hancock Foundation, Uni- 
versity of Southern California. Contribution Number 
233. Manuscript received June 28, 1957. 
Present address: School of Tropical and Preventive 
Medicine, Loma Linda, California, 
Many marine algae possess a high concen- 
tration of nonchlorophyllic pigments. Among 
these are the plant bilins or phycobilins, such 
as red phycoerythrin and the blue-green 
phycocyanin. 
The colors most often seen in the skin of 
A, californica are brown, green, red, and 
purple, all of which are characteristic bilin 
colors. The purple pigments are concentrated 
in the branchial region and are seldom if ever 
seen elsewhere externally. The basic external 
body colors are brown, dark green, and grey, 
with various gradations between them. The 
red coloration is usually observed in larger 
specimens from deeper water and is the color 
most readily proved to be a result of food 
consumption. 
In an effort to determine the relation of 
color to food, three approaches to the prob- 
lem were used: (1) the comparison of color 
pattern and food, as shown by fecal pellet 
analysis; (2) controlled feeding experiments; 
and (3) observations on the absorption spec- 
trum characteristics of the pigments. 
MATERIALS AND METHODS 
Juvenile specimens of Aplysia californica, 
ranging from 4 to 5 inches in length, were 
captured in the central shore area of Lunada 
Bay, Palos Verdes, California, and placed in 
individual pint fruit jars. As soon as a speci- 
men passed a fecal pellet the pellet was col- 
lected in a vial and the animal was released in 
an area far enough removed so as not to be 
recollected. In this manner a total of 25 indi- 
viduals was sampled. Pellets were also taken 
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