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A preliminary report on large aggregations of Turbo undulatus Solander (Gastropoda) occurring intertidally on a rocky shore in Tasmania
Invertebrata 3, Autumn 1995

Large fluctuations in the density of an intertidal population of Turbo undulatus (Gastropoda: Turbinidae) are being investigated by staff of the Queen Victoria Museum and Art Gallery. Dense aggregations of these animals occur approximately every two years in the intertidal region of a temperate rocky shore at Falmouth, E Tasmania (41°31'S, 148°16'E). The aggregations appear to be highly localised and, at Falmouth, occur on a single headland.

The foreshore along this particular section of the coastline at Falmouth consists of closely packed, large granite boulders which support very few macroalgae. During certain years, in late summer, this shoreline gradually becomes inundated with sand. The amount of sand dumped and the length of time that the boulders are covered varies annually (McManus, pers. obs.). The beginning of an increase in the density of T. undulatus intertidally appears to coincide with the commencement of sand accumulating amongst the boulders (McManus, pers. obs.). Winter storms eventually wash the sand away (McManus, pers. obs.) and the numbers of T. undulatus in this intertidal region approach zero again.

The latest increase in the density of this species was fits observed at the beginning of March 1993 (McManus, pers. obs.). Preliminary counts were recorded form haphazardly placed 25 cm² quadrats on 2 April 1993. In one such quadrat, recorded numbers of T. undulatus were as high as 431 individuals (6896 animals/m²). At this time almost every crevice between the boulders in the littoral zone was filled with live animals of T. undulatus. Further counts were performed on 18 April 1993 by which time larger sections of the shore were covered with sand the aggregations were confined to a few outcrops of rock. However, numbers of T. undulatus were still high in these last remaining areas. During 1994 no large aggregations of T. undulatus were observed at Falmouth.

Such high densities of T. undulatus have not been reported before and prominent researchers on rocky shores in Tasmania have not observed such large aggregations (I. Bennett, pers. comm.; A. Richardson, pers. comm.). Initial studies indicate that the full size range possible for animals of T. undulatus occur (up to 50 mm diameter). This implies that the aggregations are not the result of an increased recruitment per se but must be the result of a migration of animals from sublittoral populations. Because all size classes are present it seems unlikely that the animals are aggregating solely for breeding purposes. Other intertidal gastropods were found also in higher numbers than usual for Falmouth (e.g. Thais orbita, Monodonta constricta and Nerita atramentosa) (McManus, pers. obs.) but none obtained the densities recorded for T. undulatus.

The subsequent increase and decrease in numbers of T. undulatus are being monitored through a series of permanent quadrats in the area. Both numbers and sizes of the animals will be recorded over time. Factors possibly influencing the aggregation of these animals, such as food sources, are also being investigated. The researchers would be interested to hear from anyone who may have observed such an event elsewhere.

J.K. Griffith and B.J. Smith, QVMAG
T.J. McManus, Falmouth, Tasmania

Pitfall trapping
Invertebrata 3, Autumn 1995

I was recently asked to look at Tasmanian myriapods from invertebrate pitfall traps filled with ethylene glycol (antifreeze). Ethylene glycol had previously been used in 1986 by the Tasmanian Rainforest Ecological Expedition (TREE) from Southampton University. In both cases the results were appalling: specimens were poorly preserved and not at all fixed. Limbs had detached from trunks and taxonomically important details, such as setal numbers and positions, could not be recovered. Few of the specimens could be confidently identified to species. Specimens of new species, if they were present, would be of little value as types.

The argument in favour of ethylene glycol is that it doesn't evaporate from traps left open for long periods. In my opinion, this benefit comes with too high a cost. I recommend 50% ethyl alcohol with 5% glycerol as a trapping medium 'proven under Tasmanian conditions,' but Invertebrata readers may be able to suggest other alternatives to ethylene glycol.

Bob Mesibov
Research Associate
Queen Victoria Museum and Art Gallery

Digital imaging in the Tasmanian Museum
Invertebrata 3, Autumn 1995

The Invertebrate and Geology sections of the Tasmanian Museum and Art Gallery have entered the computer world of digital imaging. This is the electronic capture and storage of microscopic specimen pictures from microscope to computer.

I have commenced the storage of images of the TMAG's mollusc type collection within its database. These are mainly Tenison-Woods and W.L. May micromolluscs. Noel Kemp, Curator of Geology, is storing images of <6 mm Cretaceous shark teeth.

The process of electronic digital storage and printing of microscopic images passes through several stages. Initially the specimen is placed under the microscope and the light source and magnification are adjusted accordingly for the best picture, which is conveyed by video camera onto a TV monitor. Using either of two software programs, NIH Image 1.57 or Adobe Photoshop®, on a Macintosh Centris 660AV (which has a built-in frame-grabber) the image is acquired and saved. Depending on the applications it can also be enhanced, measured, edited, animated, printed and pseudo-coloured.

The image is then imported and stored into FileMaker Pro® along with relevant data. Additional information can be added at any time into the database. Backup laserwriter hardcopies of the records and their images are printed, catalogued and filed. (Specimens will also be photographed on the same microscope using conventional techniques as a final fail-safe.)

There are several important reasons to digitise and photograph relevant museum collections:

- Most museum specimens are irreplaceable because of their scientific, cultural and/or historical values, especially type micro-molluscs. Working from images would protect specimens from wear and tear, and save time spent between laboratory and collection.

- Printed images of specimens, particularly types, could be sent very quickly to scientists nationally and internationally either by snail mail (ordinary mail) or e-mail. Time saved by the ability to electronically recall and/or send species images would greatly enhance efficiency and ensure against loss or damage to the specimen.

- The resolution of some images is good enough for them to be used for public display and lectures, opening a window to the public of previously unviewed objects. A colour printer would be a great asset.

- Digital imaging also has applications for identification, conservation and research in other fields, e.g. geology, botany, textiles and art works. The technology is transferrable to IBM-compatible computers.

Elizabeth Turner
Invertebrate Zoology
Tasmanian Museum and Art Gallery

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