Towra Point Research Articles

Effects of predation on the size structure of the gastropod Salinator solida (Martens) populations at Towra Point, NSW, Australia

The pulmonate gastropod Salinator solida inhabits intertidal mangrove and saltmarsh communities throughout New South Wales. Studies at Towra Point and elsewhere have consistently found that the mean size and range of size/age classes increases with height on shore. Afield experiment was undertaken to test the hypothesis that predation was responsible for reductions in the mean size of individuals inS. solida populations in the upper mangrove forest. Twelve months after the establishment of fenced plots, there were significantly more individuals in the fenced plots than in unfenced or partially fenced control plots; the number of snails in the 4.1–8.0 mm and > 8.1 mm size classes had increased in the fenced plots but not in the control plots. The results suggest that predation is a major factor determining variation in population size structure by acting to significantly reduce the abundance of adults in the upper mangrove forest.

Printed in Great Britain Setal type and distribution in two Australian species of Scyphoproctus (Polychaeta, Capitellidae) and three other capitellids, with a description of Scyphoproctus towraiensis sp.n.

Scyphoproctus somalus (Polychaeta, Capitellidae) was discovered on sandbars on the north eastern side of Heron Island, Queensland. Scyphoproctus towraiensis sp.n. with similar morphological characters to S. somalus had been collected from Towra Point, Botany Bay, New South Wales. Fresh samples of both species were investigated using a number of techniques which have not been commonly used in capitellid taxonomy. Scanning electron microscopy was employed to examine the hood ornamentation of the abdominal hooded hooks, with a view to mapping the distribution of the various patterns seen along the length of the body. Several other genera were also examined for variations in setal morphology. Statistical studies of the setae showed that the setal characters tested were directly related to the size of the animal, but did not contribute to the separation of the two species. Allozyme electrophoresis differentiated between the two species of Scyphoproctus for a number of enzymes.

Factors related to the intra – and inter-specific zonation of two pulmonate gastropodsSalinator solida(Lamarck) andOphicardelus ornatus(Ferussac)

Abstract The distribution of two wetland pulmonate gastropods, Salinator solida and Ophicardelus ornatus, was studied at Towra Point and Kooragang Island, NSW. Indicator species analysis (ISA) showed that both intra and inter-specific zonation occurs. Linear discriminant analysis showed that 87.5% of the variance between five groups formed by ISA was explained by the first two discriminant functions. The first discriminant function was highly correlated with distance from shore, soil salinity and the degree of inundation at each site. The second discriminant function was correlated with cover. The pattern revealed in this study shows large S. solida to be found high on the shore in habitats of poor drainage and high salinity. Small S. solida and O. ornatus are generally found downshore in habitats of regular inundation, good drainage and good cover. Larger O. ornatus and intermediate S. solida were generally found in habitats where the environmental conditions are between these two extremes.

Temporal and spatial variability in the community structure of the fauna of four sandy beaches in south-eastern New South Wales.

Four intertidal sandy beaches with different exposures, La Perouse, Ocean Beach, Dolls Point, and Towra Point, were studied for temporal and spatial changes in faunal composition and community structure. Each of these beaches was sampled from 6 to 12 times between July 1980 and July 1981 using a 500 �m sieve. A stratified random sampling procedure across the intertidal zone isolated 40 660 individuals representing 85 species. Distribution and abundance of species were strongly influenced by tidal level. Densities changed during the year but no seasonal changes in intertidal zonation patterns were found. Changes in density were correlated with the reproductive activities of the abundant species, especially Pseudolana concinna and Exoediceros maculosus at La Perouse, and Spio pacifica at Dolls Point and Towra Point. The number of species increased from high to low tide, and also increased with decreasing exposure to wave action. Crustaceans dominated the fauna in the most exposed site and decreased in abundance with increasing protection. Ocean Beach experienced the least fluctuation in physical factors such as wave action, salinity, and temperature, and its fauna exhibited the highest diversity index (H') and evenness (J'), the most stable density, and the greatest stability in faunal composition through time. The highest densities and the most species were found at Towra Point, which also was the most protected site.