Maria J. Schreider

Anthropogenic effects on seston quality and quantity and the growth and survival of Sydney rock oyster (Saccostrea glomerata) in two estuaries in NSW, Australia

Abstract The influence that catchment development has on the growth and survival of the Sydney rock oyster, through its effect on the quality and quantity of seston was investigated in Brisbane Water and Lake Macquarie. Developed locations recorded elevated levels of dissolved nitrogen (NH 3 and NO x ) and chlorophyll a compared to undeveloped locations. Total particulate matter (TPM), particulate inorganic matter (PIM), particulate organic matter (POM), particulate carbon (PC) and particulate nitrogen (PN) were all significantly higher at developed locations in both estuaries. The PC/Chl a ratios were high, indicating that the seston was comprised of detrital matter as opposed to living phytoplankton, yet the C/N ratios were low compared to those expected of estuarine conditions. Sydney rock oysters cultured at the developed locations attained a greater mean shell length and live weight than those cultured at undeveloped locations however higher mortality rates were observed at developed locations. In Brisbane Water, seston quantity measures (TPM, PIM, POM, PC, PN) were positively related to live weight growth rate (GR) while shell length GR was negatively related to salinity. In Lake Macquarie, POM had a positive relationship with oyster live weight GR while shell length GR also had an inverse relationship with salinity. Thus, elevated seston loads associated with low salinities contributed to increased oyster growth at the developed locations where run-off is high. The concentration of the seston was therefore the controlling factor in the growth of oysters cultured in Brisbane Water and Lake Macquarie. The seston quality ratios indicated that the detrital, particulate component of the seston was high-quality food for bivalves, possibly due to associated microbial biomass. In New South Wales (NSW), a high proportion of oyster leases are located in estuaries sourced by developed catchments and the results of this study will be of interest to resource managers and oyster farmers.

Effects of height on the shore and complexity of habitat on abundances of amphipods on rocky shores in New South Wales, Australia

Abstract Patterns of abundance of epifaunal crustaceans were compared between two common brown algae in intertidal rock pools on a shore near Sydney, New South Wales, Australia. Amphipods were significantly more abundant on Sargassum globulariaefolium (which was most common low on the shore) than on Hormosira banksii (more common at mid-shore levels). Experiments tested the hypotheses that height on the shore and structural complexity of the algae were the main factors influencing patterns of abundance of amphipods. Reciprocal transplants using defaunated plants and similar experiments using artificial plants allowed simultaneous tests of these hypotheses. The abundance of a common intertidal amphipod, Sunampithoe graxon was significantly smaller on Sargassum transferred from low to mid-tidal level of the shore than on any other treatments, indicating that height on the shore affects numbers of this species. There were no Sunampithoe on Hormosira even when transplanted to low shore areas, indicating that other factors, apart from the height on the shore, are also important for this amphipod. Another common amphipod, Hyale maroubrae was generally found in greatest abundances on Hormosira transplanted from mid- to low shore and on Sargassum low on the shore, again indicating the importance of height on the shore. There was no difference in abundance of amphipods on ‘complex’ and ‘simple’ artificial plants indicating that structural complexity (as defined in this study) did not influence these amphipods.

Translational Fluctuating Asymmetry and Leaf Dimension in Seagrass, Zostera capricorni Aschers in a Gradient of Heavy Metals

Methodology for measuring translational fluctuating asymmetry (TFA) on leaves of seagrass, Zostera capricorni Aschers has been developed and tested to detect a subtle effect of environmental stress associated with heavy metal pollution on developmental instability. Our analyses showed that concentration of heavy metals (Cd, Pb, Cu, Zn, Se) in leaves and roots of the seagrass were significantly higher in the polluted location than in relatively unpolluted locations. We found significant differences in TFA between different locations, showing that the method is sensitive enough to detect spatial differences even within a rather small water body, but these differences were not associated with a higher concentration of heavy metals, i.e. plants from the polluted location did not show higher TFA. Possibly, seagrass can store heavy metals in their tissues and protect their development from the toxic effect, or the effect of heavy metals in the natural environment is confounded by other environmental factors. At...

Effects of pruning a temperate mangrove forest on the associated assemblages of macroinvertebrates

Mangrove forests around the world are being impacted by development in adjacent land and water areas. An after-control-impact study was undertaken to assess the effects of mangrove forest pruning on the associated benthic macroinvertebrate fauna. Pruning, undertaken 5 years before our sampling period, reduced the height of the forest canopy from 5 m to 1 m. Macrobenthic assemblages were sampled in September 2000 and January 2001 from two randomly selected sites within the pruned section of forest, and two sites in each of two control locations in the same forest. Assemblage composition in the pruned and undisturbed mangrove forests was not significantly different, nor were there significant differences in variability between the two areas. Similarity matrices for assemblages based on higher taxonomic groups and molluscs were highly correlated with similarity matrices for all taxa, indicating the utility of more rapid forms of assessment in this habitat. The results suggest that although short-term impacts may have occurred, no impact on macroinvertebrate assemblages was evident 5 years after the pruning.

Effect of catchment disturbance on seston quality and quantity in Brisbane Water, NSW

Abstract The direct effect of catchment disturbance on water parameters and the quality and quantity of seston were investigated in Brisbane Water, NSW Australia. Nutrient concentrations, faecal coliform levels and seston quality and quantity varied among catchments in Brisbane Water. Three of the four major catchment creeks entering Brisbane Water are sourced from disturbed catchments (Erina, Narara and Kincumber Creeks), including both industrial and residential areas, while one is sourced from a relatively undisturbed catchment (Woy Woy Creek). Monitoring occurred during wet and dry weather. After rainfall, elevated levels of nitrite/nitrate (NO x ) were recorded at the developed location at EC although the differences were not significant. Particulate nitrogen (PN) increased significantly at the developed locations at NC and EC after rainfall. The increases in these two forms of nitrogen after rainfall suggest non-point sources within the catchment. Ammonia (NH 3 ) concentrations were consistently higher at Erina Creek, even during dry weather suggesting a point source of NH 3 pollution. Variations in phosphate (PO 4 ) concentration among locations sampled were significant on only one occasion but no trends in the variation were apparent. Although not always significant, trends in total particulate matter (TPM), particulate inorganic matter (PIM) and particulate organic matter (POM) concentrations showed higher levels at developed locations, particularly after rainfall. The %POM was lower at developed locations than at Woy Woy Creek due to relatively greater increases in PIM. On some dates sampled, trends in seston quality measures indicated poorer quality seston associated with developed catchments (i.e. %PC, %PN, PC:Chl a , Chl a :TPM and PN:Chl a ) but these were significant for only some tests. The PC:PN ratio, however, did not follow the same patterns as other seston quality indicators. By altering the quantity and quality of the seston, overdevelopment can potentially lead to changes in estuarine food webs. The significance of these changes depends on factors such as the ability of primary consumers to adapt their feeding strategies in order to accommodate for shifts in the quality and quantity of food available to them.

Glassfish switch feeding from thalassinid larvae to crab zoeae after tidal inundation of saltmarsh

Saltmarsh-dwelling grapsid crabs release free-swimming larvae (i.e. zoeae) into ebbing tides during spring-tide cycles that inundate saltmarshes, where initial inundation is a cue for larval release on subsequent inundations. In a saltmarsh environment, crab zoeae are the main food for fish (including the glassfish, Ambassis jacksoniensis), which ‘fast’ at other times. This saltmarsh-feeding model was tested by obtaining glassfish from near saltmarshes in a reasonably unmodified tributary of a large temperate estuary on flood and ebb tides during the night in two spring-tide events in austral autumn of 2009. Glassfish fed only on ebbing tides, with stomachs being similarly full on both spring-tide events. Thalassinid larvae (including Trypaea australiensis) dominated the dietary volumes, especially on the night before saltmarsh inundation, presumably being released during inundation of intertidal mud and sand habitats. Although glassfish progressively ‘switched’ to feeding on greater volumes of crab zoeae (presumably released after inundation of a saltmarsh) over both spring-tide cycles, such zoeal contributions never exceeded those of thalassinid larvae. The above differences highlight that, although ebb tides trigger feeding by glassfish, this ambassid focuses on different prey in a reasonably unmodified environment. The ability of glassfish to switch prey, and thus accommodate environmental differences, helps explain their high abundance in estuaries of this region.

Higher fluctuating asymmetry: indication of stress on Anadara trapezia associated with contaminated seagrass

Seagrasses are marine angiosperms that colonize near-shore environments. Concern has arisen over increasing concentrations of heavy metals in these systems resulting from industrial and urban development due to the ability of seagrass to accumulate trace metals from the environment without showing any impact on their productivity. This may pose a threat to a coastal community because the polluted seagrass will then provide a source of contamination to seagrass consumers. The main aim of this study was to determine whether there was any detectable effect of heavy metal pollution in seagrass on associated fauna. Fluctuating asymmetry of shell structure of a bivalve, Anadara trapezia, were employed as biomarkers for this environmental study. The result from this study revealed that A. trapezia showed distinct morphological characters and high shell asymmetry in the polluted location. Thus, A. trapezia associated with seagrass may be responsive to heavy metal stress and possibly a good indicator of heavy metal pollution in this system. The present study discusses the possibility of using a more cost-effective biomarker to define areas of heavy metal pollution.