Trippa intecta in Western Australia

Dear Dave,
Published distributions of organisms, especially marine organisms, shouldn't be considered to be 'limits'. They usually reflect our knowledge of the animal's distribution, which itself may be very limited. Although there are physical and physiological barriers which do restrict the distribution of organisms, in the case of most tropical Indo-West Pacific species, like Trippa intecta, we can sometimes expect to find them way outside their normal range. On the Australian west coast, the southerly Leuwin Current, as you mention, changes from year to year, some years even sending eddies far around the southern Australian coast to South Australia. I wouldn't be surprised if Trippa intecta turned up in South Australia on the odd occasion.

At Long Reef, Sydney, in temperate eastern Australia, we have records of 40 or more species of living cowry shells (Cypraea spp), which would make you think Sydney was in the centre of the tropics. However these records have been built up over 100 years, and they are all fairly rare occurrences. It's nice to know of these 'extra-limital' finds but on both the east and west coasts of Australia there is a very broad buffer zone where the tropical and temperate faunas mix to varying degrees each year.

Bill Rudman.