104 
PACIFIC SCIENCE, VoL XVII, January 1963 
to have ingested a quantity of Pelvetia fastigi- 
ata, a food plant that was consistently refused 
by aquarium-confined specimens (Winkler, 
1955 ) . The diet of the young of this species has 
not been determined. 
DISCUSSION AND CONCLUSIONS 
In northern California Aplysia californica is 
known principally from protected bays and es- 
tuaries such as Elkhorn Slough, Bodega Bay, 
and Tomales Bay. In these areas, beds of Ulva 
and Enteromorpha often occur abundantly, and 
J. J. Gonor has reported to us in a personal 
communication that A. californica lives in these 
beds and apparently uses both plants for food. 
Marcus (1961), reporting upon specimens 
from Bodega Bay and Tomales Bay, indicated 
that A. californica feeds on sea plants, especially 
Zoster a and C odium. MacGinitie (1935) stated 
that sea hares in Elkhorn Slough fed on Zoster a, 
but in subsequent personal correspondence has 
indicated that they also fed on Enteromorpha, 
which is sometimes the most prevalent plant in 
the slough. However, he also observed that at 
certain seasons the alga was absent from the 
area while Zoster a remained. He concluded, 
then, that Zoster a was their principal staple 
food. 
In southern California the eel grass, Zoster a, 
does not occur intertidally on the open coast 
and is uncommon in bays, and although the 
similar surf grass, Phyllospadix, grows in pro- 
fusion at low water levels it is rarely ingested 
by sea hares. Likewise, neither Ulva nor Entero- 
morpha is abundant in open coast habitats of 
southern California, and, although captive sea 
hares showed preference to Ulva or Enteromor- 
pha over any other food offered them in the 
laboratory, in nature they resort to feeding on 
red algae, which are almost their exclusive food. 
Young southern California sea hares seem 
to eat a wide variety of seaweeds depending 
upon the flora in their immediate surroundings, 
although some species are apparently habitually 
refused. As they grow older and wander farther J 
they seem to become more selective in their 
food habits and develop a behavior pattern that 
is difficult to break under changed feeding con- ; 
ditions in the laboratory. 
It has been generally observed that Aplysia 
californica in northern California is of larger ; 
average size than in southern California, and 
the senior author considers that this larger size, 
as well as the difference in color (Winkler 
1959^), results from dietary differences. Ex- 
perimental evidence for the variation in size 
similar to that for color variation is needed to j 
confirm the homogeneity of the two forms. I 
Two distinctive dietary factors offer themselves 
for study: (1) the comparative nutritive value 
of a high Ulva-Enteromorpha component in the 
diet during spring and summer; (2) the effect 
of almost exclusive feeding on the marine grass, 
TABLE 2 
Presence and Relative Abundance of Several Algae in Crops 
OF Aplysia californica FROM DOHENY Beach, CALIFORNIA 
COLLECTION 
NO. 
Hypnea 
valentiae 
Jania 
tenella 
Corallina 
gracilis 
Corallina 
pinnatifolia 
Corallina 
vancouveriensis 
Sphacelaria 
sp. 
Lauren cia 
sp. 
Lithothrix 
aspergillum 
D-02 
XXX 
X 
D-04 
XX 
XX 
D-06 
X 
XXX 
D-08 
X 
iiii 
X 
X 
X 
X 
X 
D-20 
xxxx 
D-21 
xxxx 
D-27 
xxxx 
D-28 
XXX 
1 x 
