Variation in diet of the West coast rock lobster (Jasus lalandil): influence of rock-lobster sex, size and food environment.·

Abstract

Few studies of rock-lobster diet have included analyses of mature females or juveniles of

either sex. This study focused on the diet of male and female West Coast rock lobsters

(Jasus lalandil) in three size classes (viz.: 10 - 35 mm CL (carapace length) - small,

40 - 59 mm CL - medium and 70 - 85 mm CL - large), using visual analyses of stomach

contents. The principle aims were to examine potential differences in diet between:

(1) male and female rock lobsters; (2) changes in diet with size and (3) a comparison of

rock-lobster diet between areas of known fast- and slow-growth rates.

The primary prey items of rock lobsters are shown to be the black mussel (Choromytilus

meridiana/is), ribbed mussel (Au/acomya ater), barnacle (Notomegabalanus algicola),

sea urchin (Parechinus angu/osus), sponge and crustacean remains. There was no

difference in diet between male and female rock lobsters within any size class. BrayCurtis

similarity dendograms and Multi-Dimensional scaling plots revealed differences

between small, medium and large rock-lobster diets. Small rock lobsters consumed

mainly ribbed and black mussels, whereas medium rock lobsters consumed higher

percentages of barnacle and sponge. Sea urchins comprised a substantial percentage

of large rock-lobster diet. ANOSIM (Primer v 4.0) established significant differences

(p < 0.05) amofng diets of the three size classes. Differences in diet were also

observed between areas of fast- and slow-growth rates, but these were limited to the

small and medium size classes. Key prey items responsible for this difference in diet

were black mussel and rock-lobster remains. The gut fullness index decreased with

increasing rock-lobster size.

In conclusion, there appears to be no difference in diet between male and female rock

lobsters, regardless of their size. However, rock-lobster diet does appear to vary with

size. The inverse relationship between gut fullness indices and size, suggests that small

rock lobsters, which have a higher moult frequency, feed relatively more frequently than

larger rock lobsters. Diet composition plays a role in determining the growth rate of rock

lobsters from different areas.