California Xanthidae — Knudsen 
13 
defenseless or unable to capture food, and even- 
tually die. 
On a few occasions zoeal ecdysis was seen 
microscopically. The writer’s notes and the 
examination of zoeae preserved while partially 
through ecdysis reveal that the process is essen- 
tially the same for larvae and adults (Knudsen, 
1957: 133-142). The carapace is elevated dor- 
sally above the abdomen. The abdomen and 
pereiopods are drawn out of the old skin as the 
new zoea expands upward and backward. As the 
zoea backs out of the split in the old skin the 
new dorsal spine is extracted from the old case. 
The eyes, antennae, and rostral spine are the last 
parts to be withdrawn. The haemocoelic pressure 
quickly extends the body to its new size as the 
molting process is completed. Once free of the 
old skin the zoea swims away and begins feeding 
in less than a day’s time. 
'Enemies 
To an individual pelagic larval crab, or any 
other animal, every organism is a possible source 
of food because it is smaller, or of neutral status 
because of equal size and strength, or a predator 
because it is larger. The diatom is generally 
thought of as the basis of the oceanic food chain. 
Above this come the tiny, filter-feeding animals, 
which in turn, serve as food for larger planktonic 
animals. Thorson (1950: 19) names depreda- 
tion by other animals as the most important 
form of wastage of planktonic larvae. The filter 
feeders, from tiny crustaceans on up to fishes 
(herring, mackerel) and even whales, probably 
take the great percentage of larvae. 
Obviously the xanthid zoeae are no exception, 
but fall prey to any stronger or larger predator. 
In the laboratory zoeae and megalops fed fre- 
quently on other zoeae. Many first zoeae were 
seen to eat the dorsal spine of other living first 
zoeae. When Artemia larvae became too large 
they too preyed on the zoeae. Copepods experi- 
mentally placed in culture jars also took a toll 
of zoeae. 
Mortality of Larvae 
Table 2 gave approximate numbers of eggs 
produced at one time by various sized females. 
An investigation of the gonads and sperma- 
thecae of ovigerous females suggests that more 
than one egg mass is carried per year. Judging 
from the length of the breeding season, it ap- 
pears that Lophopanopeus and Paraxanthias pro- 
duce more than two egg masses each year. Thus 
a 40-millimeter female P. taylori may produce 
up to 120,000 eggs per year. 
There is no direct method of measuring the 
mortality of pelagic larvae. Thorson ( 1950: 12- 
19) states that food conditions, temperature 
conditions, metamorphosis, unfavorable current 
transport, and predators are the sources of waste 
of pelagic larvae. Where commercial records are 
kept for a species for a long period of time some 
estimate of the total adult population, the yearly 
spawn, and the larval mortality can be made. 
However, if the entire population of a species 
remains relatively constant over a long period 
of years, then, barring short-term fluctuations, 
the following supposition can be made: only one 
pair of F-l individuals produced throughout the 
life span of one breeding pair reaches maturity 
and reproduces. Thus the annual larval mortality 
rate equals the total number of eggs produced 
by an entire species population that year, minus 
the total mortality of mature individuals of that 
species. Periodic fluctuations in adult popula- 
tions, by this line of reasoning, are due to a 
modification of one of the larval waste factors 
outlined above, or to some change in conditions 
which affect the early crab stages. In the case of 
the Xanthidae, these factors are the total amount 
of habitat available, food conditions, tempera- 
ture conditions which may speed up or retard 
development and reproduction, population pres- 
sures, depredation, and competition for food. 
Thus, the reasoning used is based on a long- 
term basis in which fluctuating conditions and 
the resulting population change will balance out. 
Current Transport 
There are two main ocean currents which are 
responsible for water movement off the coast of 
California. These are the California Current, 
which transports water to the south, and the 
Davidson Current, which transports water to the 
north. The California Current prevails from 
February to October during the seasons of west- 
erly winds and upwelling. In the fall when the 
westerly winds and upwelling cease, a counter 
current develops which, in November through 
