The remote Abrolhos Islands in Western Australia are famous for being the southernmost spot on this planet where corals reefs occur. The in recent years been visited only by few diving expeditions. Our hope was to find specimens of the elusive Zoila ketyana bataviensis Lorenz & Morrison 2001, recently named after the Dutch sailing ship Batavia which sank in the Abrolhos in 1629. Also, we wanted to revisit the spot in which years ago the population of Zoila ketyana lutea was discovered, in the southwest of Dirk Hartog Island (Shark Bay area). Our route as planned ran from Fremantle (Perth) to the Abrolhos, eight days later to Geraldton to get fuel and food, and northwards along the Zuitdorp Cliffs to Shark Bay and Dirk Hartog Island. After a week in the north we went back home doing dives near Kalbarri and Dongara.
The dive boat Lionfish IV belongs to the Perth Diving Academy. It is 24 m long, conveniently carrying 40 divers, and is equipped with diving compressors, modern GPS navigation computers and an underwater video camera needed for finding the right habitats in depths ranging from 33 to 46 metres.
Our team consisted of four crew members and twelve divers. The trip from Perth to the Abrolhos takes a full day. The islands are flat, with bare vegetation and untouched fringing coral reefs. Some of the islands are temporarily inhabited by lobster-fishermen.
The diving is not exactly easy, as all dives for Zoila in this area are deep and two to three dives a day are the rule. Zoila ketyana bataviensis lives exclusively on Geodia, a soft, compact sponge of reddish-brown to purple colour with the shape of an amphora turned upside down. It is a very rare shell, so after eight days of intense search, we brought up a total of only eleven specimens, three of which in a condition anywhere near fine/f+, the rest being of bad quality due to heavy fish bites or algae encorporated in the shell's nacre.
The scarcity (there are no "hot spots" where the shell is more common - they seem to be very scattered and rare even in their habitat), and the costs and effort involved in finding a good shell will always make the bataviensis one of the rarest of the Zoila, along with mariellae, perlae and rosselli edingeri. Less than thirty specimens of bataviensis have ever been found by divers, and it is undecided whether another trip to the Abrolhos will be made in order to find more specimens: for the participating divers the trip was a financial fiasco. And here is why. It was planned that after visiting the Abrolhos, where finding a shell is really hard and a matter of pure luck, we would go nother to the southwestern end of Dirk Hartog Island. This is the area where the sought after ketyana lutea was found in fair numbers, every diver would have a good chance of finding perhaps half a dozen shells to pay for the trip. The area has not bery heavily collected so the expectations were high when we finally reached the spot and the camera showed promising grounds. Everyone went off in the water. After a couple of minutes in 43 m I realized that in the area I dove there was perfect habitat, but no shells.
I returned to the boat to find that noone had found a shell. The luteas were gone. Instead, we found Lyncina carneola, a warm water species, on the underside of the Geodia, where the luteas were supposed to be. Continued search in the vicinity produced not a single Zoila, even the more common species such as rosselli were gone. The same phenomenon had been observed in the north, e.g. at Exmouth, where the lovely eludens used to come from, or at Bernier Island where ketyana hypermarginata used to live, as well as the area around Point Quobba, famous for its jeaniana and the golden rosselli edingeri - all these shells have not been found since years. The sponges are still there, but the shells are gone. Overcollecting has probably weakened the populations, then some mysterious desease or ecological catastrophe must have wiped them out completely. Now it seems to go southward, wiping out even those populations not heavily collected, such as the luteas.
Nevertheless, the trip produced some interesting and also some new things. On our way back, we made a dive near Kalbarri, in approximately 38 m depth. On this dive, a very interesting specimen of friendii friendii was found, very far north of the known range, alongside a very slender but otherwise typical jeaniana. The two were found on different types of sponge. Finding these shells together in one place proves that they are separate species, sharing the same geographic spot and the same habitat but specializing on different hosts. The jeaniana proved to be a distinct new subspecies for that area and was named jeaniana thalamega Lorenz 2002.
on right: Zoila friendii, both from near Kalbarri, 38 m.
Many thanks to Hugh Morrison and to all the other fellow divers for the great time we had, to the crew of the Lionfish IV and Jeff for the excellent cooking.