Browsing by Author "Innes, Sheona"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Contesting the termite hypothesis for the origins of heuweltjies in Clanwilliam, South Africa
    (2010) Innes, Sheona; Midgley, Jeremy J; Cramer, Michael D
    The age and origins of large earth mounds (locally termed "heuweltjies") is under debate, with ages being proposed for between 4500 and 30 000 years old, and hypotheses including zoogenic and geological origins of the mounds. The widely accepted hypothesis for the origins of the heuweltjies found in the South Western Cape of South Africa is that mounds are ancient termitaria, belonging to the southern harvester termite Microhodotermes viator. Our idea was to use rocks and stone layer profiles to determine approximate ages of the heuweltjies as well as to gather evidence to either support or refute the termite hypothesis. We excavated ten mounds in Clanwilliam, South Africa, to gather stone and rock profiles throughout the mounds, as well as digging a trench through a heuweltjie with bedrock as its matrix in order to determine the extent of the bedrock into the mound. No stone layers as such were found. What we did find was that the mounds are a whole order of magnitude greater in volume than large termite mounds made by the northern harvester termite Macrotermes in tropical regions, and many of the mounds contain large rocks both throughout the mound as well as on the surface. The trench cut through the mound on bedrock revealed the bedrock extending all the way to the centre of the mound, on the same level as the surface of the surrounding matrix. This evidence can be used to refute the termite hypothesis for the heuweltjies of Clanwilliam as it is virtually impossible for termites to move rocks up to 25 kg to the top of a mound, and mining soil from beneath a mound with bedrock at its base is an impossibility.
  • Thumbnail Image
    Item
    Open Access
    Tropical intertidal seaweed turf communities of Jesser Point, Sodwana Bay, South Africa
    (2010) Innes, Sheona; Bolton, John J; Anderson, Robert J
    Algal turfs play an important role in both tropical and temperate reef ecology, supporting a diverse array of macrofauna as well as being primary producers within both intertidal and subtidal ecosystems. Biodiversity and biomass patterns of the intertidal algal turfs at Sodwana Bay, South Africa have not yet been established so this study was undertaken to investigate these. It was hypothesised that both biodiversity and biomass would decrease with increasing height along the shore, as well as that sediment would have an effect on the community composition of the turfs. The community was sampled over a vertical range of 1.2 m and found to be dominated by the red alga Jania intermedia (24.21 % of total algal coverage) followed by Tolypiocladia glomerulata (18.05 %), Dictyota sp. (13.39 %), Jania adhaerens (12.32 %) and Sphacelaria tribuloides. (5.83 %). No significant vertical zonation patterns were found, though certain species showed vertical trends such as Asparagopsis taxiformis and Sphacelaria tribuloides, which occurred in greatest biomass lower down on the shore, while Tolypiocladia glomerulata occurred higher up on the shore. Sand was found to affect certain species more than others, with Tolypiocladia glomerulata, Jania adhaerens and Asparagopsis taxiformis occurring in greatest biomass when the amount of sediment found in the quadrat was low, while Sphacelaria tribuloides. showed the opposite pattern and Jania intermedia showed no distinct pattern. Sampling took place over 1.2 m vertical height along the shore at spring low tide therefore covering 60 % of the intertidal zone vertically (maximum tidal range in South Africa is 2 m). It is therefore possible that the turfs are the cause of a decline in zonation by remaining damp and decreasing desiccation gradients vertically along the shore.