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Conchology Section |
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Conchology Section |
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Glenys welcomed members to the June meeting. She reported with great glee that a group organised by Betty are about to leave Auckland’s winter for Australia, timed to enjoy shell shows. We wished them a pleasant trip but pointed out they would be required to give a talk at a future meeting!
The recent algal bloom from Beachlands around Auckland’s eastern beaches and Long Bay, North Shore was discussed. The fine algae, composed of a green and a blue green species, grows across the intertidal areas in vast quantities. When washed ashore the deep rotting piles cause a severe smell. Following this prolific food source are populations of the sea hare Bursatella leachii. Mixed in the wash up are the spawn, looking like tangles of green knitting wool. Experts do not agree on the cause of the bloom. Is it a natural phenomena or a sign of pollution or temperature change?
Bruce Hazelwood has been doing some interesting land snail collecting in the Waitakere Ranges.
Margaret Morley and Bruce Hayward spoke briefly on a recent survey done in the Matarangi district, on the north-east coast of Coromandel. Gale force winds and rain were not ideal for collecting!
SPEAKER FOR THE EVENING was Bruce Hayward on the Intertidal and subtidal biota and habitats of the Waitemata Harbour. A map with accompanying notes has been published with funding from the Auckland Regional Council. Bruce and the nine co-authors compiled the map and notes between 1993 and 1998. Ninety bottom samples were dredged from above and below the harbour bridge planned to give a broad coverage of the subtidal area and also coincide with the dredge stations used by Dr. Powell in the 1930’s. We enjoyed the slides, especially the one of Bruce and Brett Stephenson hand hauling from their small aluminium dingy- “the largest research vessel in New Zealand”! All live organisms retained after sieving were hand picked, identified and counted. This produced a data set of over 20,000 specimens in over 3000 different taxa.
The intertidal mapping was done mainly on foot but some of the long mangrove fringed inlets were surveyed from a dingy. Eighteen different habitats and associations are described, these include salt marsh meadow, mangrove forest, Waitemata sandstone reefs, wharf piles, cockle shell banks, soft gloopy mud and basalt reefs and walls. The map shows the great extent of man-made edges to the coast in the central city and adjacent shores. The periwinkle Nodilittorina antipodum and Nerita atramentosa find this a suitable habitat.
During the intertidal surveys we were soon able to visually distinguish some of the mapping units like the muddy fine sand flats with its abundance of mud snails Amphibola crenata. The units were later confirmed by comparison with aerial photography. Some areas close to the city surprised us with by the species present. Who would have expected to find a live Alcithoe arabica laying its egg case within view of the harbour bridge?
The main study lead to several specific offshoots.
Bruce showed graphs of the growth of the horse mussel Atrina zelandica living in the Rangitoto channel.
Over a two year period Bruce and Margaret measured the growth rates of the small introduced bivalve Theora lubrica in Hobson Bay, Orakei. Once a month quadrats of low tide mud were sieved and the specimens of Theora measured. This involved a lot of soft gloopy mud! Gradually size graphs revealed that in New Zealand this species grows about 1mm a month and reproduces all year. The population cycles were explained by aquarium experiments that showed the mud crab Helice crassa can eat up to seven Theora a day!
Another study measured the reappearance of the eel grass Zostera in the Cox’s Creek area. The newly emerging circular beds spread out and in some cases have coalesced. This species was widespread throughout the harbour until the 1950’s when it was decimated by a fungal disease.
A large map or notes with a small map can be obtained from the Auckland Regional Authority. The biota studies are in press. Thank you Bruce for an interesting lecture backed up with lots of visuals.
SHELL SHOW A REMINDER THAT YOUR REGISTRATION FORM MUST BE RETURNED TO PETER BY 30 SEPTEMBER. Our dates coincide with a Summer Festival put on by the Plaza business community. This will attract extra members of the public and provide cultural and club displays, art and craft exhibitions over the weekend. Your copies of the Shell Show competitions are enclosed. Please plan an entry and/or pass them around to friends. Schools have been contacted direct.
C.S.A.M. ADDRESSES (enclosed)
Thank you to Peter who did the typing.
CHITON EXCHANGE
If you are interested in exchanging chitons with a collector in Belgium contact Margaret for details and the exchange list or reply direct to Bruno Anseeuw, Mispelstraat 18, 9820 Merelbeke, Belgium.
WANTED
Paul asks if anyone has a wooden shell cabinet for sale. He would prefer it to be rimu, or kauri. He could restore an old one so its condition is not important. Ph (09) 849 5311.
FIELD TRIP
Mark these two dates in your calender: Sunday Sept. 17, help is needed to take a Forest and Bird group around Mellons Bay, and the next weekend Sept. 23 or 24 to pick up rubbish at a Manukau Beach, details to come.
NEXT MEETING 11 JULY 2000 7.30PM At the Auckland War Memorial Museum.
Entry by the Administration door between 7:15 and 7:45pm. No late admittance.
Mixed bag night. Doug Snook will give a talk about some of his more spectacular and recently acquired overseas shells. Margaret will show a selection of slides from the Subantarctic to the Kermadecs. Please bring a tray of overseas shells. It would be a good night to raise any identification problems or any other club matters. There will be a door prize of Cypraea cervinetta, collected at Panama.
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