1. Department of Zoology; University of Cambridge; Cambridge CB2 3EJ UK
2. School of Biological Sciences and Centre for Marine Science; University of Queensland; Brisbane Qld 4072 Australia
3. Department of Zoology and Entomology; Rhodes University; Grahamstown 6140 Republic of South Africa
4. Knysna Basin Project; Knysna 6570 Republic of South Africa
5. Institute of Marine Sciences Laboratories; University of Portsmouth; Eastney, Portsmouth PO4 9LY UK