242
THE ESSEX NATURALIST
form of tube building worm (Pectinaria belgica), as great sources
of attraction and that their other food was similar to that of
the brown shrimp. He concluded with the statement that the
young pink shrimps which are hatched along the parallel sand-
banks facing the Essex coast have for safety and food the
abundant marine vegetation, the hydroids (Sertularia,
Plumularia, etc.), and, in addition, Foraminifera, minute annelids,
molluscs and crustaceans.
The examination of 650 stomachs of pink shrimps, taken
from monthly samples trawled from Clacton-on-Sea, River Crouch
and Thames grounds, during 1950 and 1951, showed that 65 to
85 per cent. of their food was small marine worms, of which 30-52
per cent. was definitely recognised as "ross". This worm (S.
spinulosa) has some characteristic features which are not present
in other worms and consequently it was easy to identify them
in the stomach of the pink shrimp. It appears that the animal
crawls over the colonies of "ross" and cuts off, with its first pair
of legs, the protruding heads of the worms. Occasionally two
heads of this worm were found in the stomach instead of the
usual one. Pectinaria sp., which Murie stated to be an attraction
for pink shrimps, has been found in only one individual. The
remaining diet of the pink shrimp was composed of small
crustaceans (mainly amphipods), lamellibranchs (young mussels),
parts of white-weed (Sertularia), sand particles, algae, and various
other forms (crustaceans and fish eggs). One stomach contained
eight small mussels, the largest being 1/10 of an inch long.
The pink shrimp has only one continuous spawning season,
commencing about the beginning of November and terminating
in April or May. The larger size groups lay first, followed by
the females which will spawn for the first time in their life, and
before completing a full year. The eggs when first laid are
emerald green. With the gradual development the emerald
colour disappears and becomes light green with a tint of light
violet. When the eggs are laid in November they measure
approximately 0.80 by 0.60 mm. With the passage of time the
size increases, and by April and May the majority of the eggs
measure between 1.00 and 1.30 mm. in length. The number of
eggs carried by the female vary according to size of the parent.
The smallest number of eggs found to be carried by a female
was 136 and the largest 3,800, which is considerably less than
laid by the brown shrimp.
When the larvae are hatched out in March or April they
measure about 1/10 of an inch in length. By July, sometimes as
early as late June, some young shrimps are big enough to be
caught by trawl nets. However, it is during the summer months
that they grow rapidly, some of them becoming 11/2 to 13/4 inches
long by the end of November. Female pink shrimps grow quicker
than males. Growth appears to stop by November and Decem-
ber, and does not start again until the following March or April.
Growth during the following two years is slow. The largest