Biometry and size distribution of Chrysaora hysoscella (Cnidaria, Scyphozoa) and Aequorea aequorea (Cnidaria, Hydrozoa) off Namibia with some notes on their parasite Hyperia medusarum

Novel data on the biometry, size distribution and parasites of Aequorea aequorea and Chysaora hysoscella are provided from investigations conducted during summer and winter in the northern Benguela ecosystem. The relationship between mass and diameter of C hysoscella did not change on a seasonal basis, and this possibly reflects the aseasonal nature of the food environment. The changes in the size structure of C hysoscella across the shelf and with depth agree with postulated population maintenance strategies in the region. Aequorea aequorea was not strongly parasitized, but C hysoscella was subject to occasional parasitism by Hyperia medusarum, especially in winter when C. hysoscella is thought to reproduce. Parasites were distributed in a typical, negative- binomial manner on their hosts, but load was independent of host size. As medusae increased in diameter so H. medusarum tended to move from other tissues to the gonads.