8 
PACIFIC SCIENCE, Vol. XVIII, January 1964 
will be found highest up on the rocks while the 
females are more timid and remain along the 
lower sides of the rocks where they can reach a 
hiding place in case of an emergency. As the 
tide comes in and covers the zone, these crabs 
move about in large numbers, yet become quite 
secretive if the presence of the collector is ob- 
vious. The behavior of the males as compared 
with the females was especially noteworthy in 
H. nudus. When females of this species were 
captured upon the rocks at night they quickly 
autotomized appendages in order to escape. 
Males, on the other hand, were quite reluctant 
to autotomize an appendage but rather would 
resort to bluffing or actual pinching with the 
chelae. 
Hemigrapsus nudus 
FOOD AND FEEDING HABITS: Thirty-four 
specimens were collected in the Titlow Beach 
area for stomach analysis. The animals were 
preserved with a 5% formalin solution to insure 
a quick and complete saturation of the stomach 
contents. In the laboratory the stomachs were 
removed and the contents examined under dis- 
secting and compound microscopes. Of the 34 
animals examined, 4 had completely empty 
stomachs while 3 had only partially full stom- 
achs. The largest portion of the gut contents 
was made up of marine algae, while the second 
largest portion consisted of inorganic material 
such as sand grains. The least abundant material 
found in the gut content consisted of animal 
tissue. Amongst the algae, diatoms and desmids 
made up the greatest portion of material. Some 
species of green algae ( Ulva sp. and Enter o- 
morpha sp.) were frequently found. To deter- 
mine the source of the diatoms and desmids, 
scrapings were made along the sides and tops of 
rocks within the habitat of this species. A micro- 
scopic analysis of these scrapings demonstrated 
that the algae present were identical with those 
found in stomachs of H. nudus . Furthermore, 
diatoms taken in sea water samples did not 
match those found in the stomachs. Examination 
of the rocks showed that young fronds of the 
above-named green algae were frequently pres- 
ent. Our observations have shown that this 
species gleans from the surface of the rock using 
the large chelae. The feeding method is pri- 
marily the same as that described by Hiatt 
(1948:178) for Pachygrapsus eras sipes. Crus- 
tacean exoskeletons made up the most notable 
portion of the distinguishable animal tissue 
within the gut contents. Amphipods could be 
recognized and fragments of other similar ar- 
thropods. were present. No attempt was made 
to determine the exact species of either the 
animal or plant material, for the source of this 
material seemed to be the most important thing 
in this instance. Abundant small arthropods 
exist wherever Hemigrapsus feed and thus these 
animal fragments are probably accidental in 
their appearance. Hiatt (1948:178) describes 
Pachygrapsus as being an active predator which 
will frequently attempt to capture living ani- 
mals. The present writer has seen Pachygrapsus 
on numerous occasions in California in the act 
of eating freshly killed animals, even large in- 
dividuals of newly-molted Cycloxynthops. No 
such observations have been made for H. nudus 
in the field, though there is little doubt that 
this species will capture and eat animal material 
when it is available. On occasion this species 
was seen feeding on dead animal tissue. How- 
ever, the food supplied by scavenging probably 
contributes very little to the total volume con- 
sumed by this species. Feeding activities are 
most readily observed at night. When in total 
darkness crabs will migrate from their hiding 
places and feed along the sides and tops of 
rocks. Hemigrapsus may confine much of its 
feeding to periods of low tide to prevent the 
tiny diatoms from being washed from the chelae, 
although this species does feed while under 
water. H. nudus is definitely a herbivore, but 
obtains a small portion of its food as a predator 
and scavenger. 
SYNOPSIS OF REPRODUCTIVE ACTIVITY: Figure 
1 shows that oogenesis in H. nudus begins in 
the fall and continues into the first weeks of 
January. Numerous observations of copulation 
were made during the later weeks of December 
and into the first weeks of January. Egg deposi- 
tion begins very early in January and the rate 
of deposition increases swiftly until over 70% 
of the females are ovigerous at the end of that 
month. The number of females bearing fertilized 
eggs on the pleopods increases very slowly from 
this point on, until a peak of 98.6% is reached 
in the early weeks of April. Hatching very 
