A study of the gnammas (rock pools) in some granitic outcrops in central Victoria, with a comparison of their invertebrate communities across southern Australia

Abstract

Gnammas in central Victoria occur at Kooyoora, Terrick Terrick, Mt Pilot near Chiltern and Bald Rock near Euroa. Though similar structurally and with similar hydroperiods to those in the Western Australian Wheatbelt and on Eyre Peninsula (EP), South Australia, many are smaller and all have fresher waters. Momentary species richness in pan gnammas range from 2.7 at Bald Rock to 9.3 at Terrick Terrick and in pit gnammas from 7.6 at Kooyoora to 15.3 at Terrick Terrick. These figures are significantly lower than figures of ca 30 for WA pans and ca 10 for EP pans, but ambivalent for pits, cf 12 in WA, and 9 on EP. Central Victorian gnammas have only one endemic species compared with many in WA and a few on EP. Species seem to have few special adaptations for life in Victorian gnammas, compared to many in WA. Factors thought to be influencing these differences include habitat size (a function of site age), number of gnammas per rock exposure (habitat variability and availability), and past climatic fluctuations (promotion of speciation). All these factors enhance diversity in WA, but mostly inhibit it in central Victoria, with Eyre Peninsula being intermediate.