Thesis (Ph.D.) - University of Queensland, 1997. / Includes bibliography.

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Coastal ecosystems continue to come under increasing pressure from human activities and the input of anthropogenic substances. This is being realised in a number of areas where eutrophic conditions begin to dominate and phenomena such as toxic algal blooms increase in frequency. Amidst this situation there is a growing need to understand how ecosystem components such as benthic fauna might respond to these conditions and how we might better use some of these components as indicators of ecosystem perturbation. In this context the current study examines the distribution and abundance of sediment meiofauna in seagrass beds at two different locations in Moreton Bay estuary. This ecosystem presently receives significant anthropogenic inputs from the Brisbane River and other sources draining the greater Brisbane catchment and adjoining areas. The main aims of the study were to characterise the distribution and abundance of meiofauna in these sediments and to also examine some of the main factors influencing these features. Also, it was intended that on examination be made of the influence that blooms of the cyanobacterium Lyngbya majuscula might have on meiofauna abundance and distribution in these areas. Blooms of this alga are an increasing feature of the Moreton Bay estuary and potentially represent a strong influence on a range of habitats and organisms within the ecosystem. In considering the physico-chemical aspects influencing meiofauna, sediment grain size and nutrient levels were shown to have some effect on distribution and abundance although this varied between species and location. Further, the grain size of the sediment and the total organic carbon did not change significantly between bloom and non-bloom periods and but total nitrogen and C/N ratio did show a change. In regard to the observed effects of the L. majuscula blooms, a negative impact was observed on copepod and nematode abundance and distribution. In both cases their abundance was considerably smaller during the bloom period. Notably, polychaetes showed no effect from the bloom?s occurrence. The results also indicate that during the bloom the meiofauna were distributing shallower in the sediment, probably due to the hypoxic conditions that the bloom may have created. Moreover, the impact of the bloom was more pronounced in the smaller size classes for the meiofauna and suggests that these classes are more sensitive to the conditions generated by the deposited bloom material. Under Multiple Regression Analysis nematodes and polychaetes were positively correlated with sediment nitrogen concentration, while copepods were not. Also, during the bloom the nitrogen concentration in the sediment increased but the abundance of nematodes showed an opposite trend. The general negative effect of the bloom on the total fauna might be the responsible for this result. An attempt was also made to assess whether the nematode:copepod ratio (Ne:Co) could be used in this ecosystem as an indicator of pollutant input or habitat disturbance by the algal bloom. This ratio has been used elsewhere with some success. Results from this study indicated that this ratio has only limited value as an indicator in the study situation and that the concomitant influence of sediment grain size and nutrient levels lead to a potentially misleading interpretation of the results that the ratio provides. The interactions between meiofauna, the prevailing physico-chemical and biological characteristics of the sediments in Moreton Bay are clearly very complex. The influence of phenomena such as the Lyngbya blooms adds to this complexity but, in the current study, this was seen to clearly have an effect on both animal abundance and their distribution. In this regard, the present study has identified the key areas of influence from the algal blooms and has also highlighted the need to further research these important animal groups so that we may better understand how the benthos, and thus the wider ecosystem, might cope with pollutants and anthropogenic disturbances.

The present study was aimed to find out if there is any symbioses between C.australe roots and mycorrhizal fungi. This research also aimed to investigate the effect of Arbuscular mycorrhizal fungi on the growth of C.australe and the yield of alkaloid castanospermine. The rhizosphere soil and roots of C.australe from various sites in Sydney were collected. Roots were stained with vital and non-vital stains for assessment of mycorrhizal infection. The result indicated that AM fungi symbiotic associations with the roots of C.australe, producing arbuscules and vesicles in the root cortices. By wet sieving and decanting of rhizosphere soil, spores and sporocarps of AM fungi, were recovered. The spores mainly belonged to the genus Glomus. A correlation study was conducted to determine the relationship between the AM infection percentage in the roots and the Castanospermine amount in the leaves and seeds of the field grown trees. The results showed that there is a positive relationship between the castanospermine amount in the seeds and AM infection percentages in the roots. The effect of phosphorus on the yield of castanospermine was also investigated. The results indicated that phosphorus do enhance castanospermine at certain levels, but a further increase in phosphorus application resulted in reduced AM infection. It was found that AM has a great effect on the growth and production of C.australe and biosynthesis of castanospermine. / Master of Science

The role of autotrophic production in different coastal habitats in the production of fish in estuaries is an important consideration in coastal management and conservation. In the estuarine waters of the Australian east coast, many economically important fish species occur over mudflats lacking conspicuous vegetation. I used stable isotope analysis to examine where such fish ultimately derived their nutrition, in the subtropical waters of southern Moreton Bay, Queensland, Australia. I first tested traditional processing methodologies of autotroph samples, in this case of mangrove leaves, and examined variability in mangrove isotope values at different spatial scales. Mangrove leaves processed using time-consuming grinding showed no significant difference in isotope values than coarsely broken leaf fragments. Isotope values of green leaves were not meaningfully different from yellow or brown leaves that would normally be the leaves that actually dropped on to the sediment. Future analyses therefore can use green leaves, since they are more abundant and therefore more easily collected, and can simply be processed as whole leaf fragments rather than being ground to a powder. Carbon and nitrogen isotope values varied at several spatial scales. The proportion of variability partitioned at different scales varied depending on the species of mangrove and element (C or N) analysed. To properly represent a geographic area, isotope analysis should be done on leaves collected at different locations and, especially, from different trees within locations. The autotrophic source(s) supporting food webs leading to fish production on mudflats might be either in situ microphytobenthos or material transported from adjacent habitats dominated by macrophytes. I tested the importance of these sources by measuring ?13C values of 22 fish species and six autotroph taxa (microphytobenthos on mudflats, and seagrass, seagrass epiphytic algae, mangroves, saltmarsh succulents and saltmarsh grass in adjacent habitats) in Moreton Bay. I calculated the distribution of feasible contributions of each autotroph to fishes. All fish ?13C values lay in the enriched half of the range for autotrophs. For over 90% of fishes, the top three contributing autotrophs were seagrass, epiphytes and saltmarsh grass, with median estimates of approximately 60-90% from these sources combined. Seagrass was typically ranked as the main contributor based on medians, while epiphytic algae stood out based on 75th percentile contributions. The other three sources, including MPB, were ranked in the top three contributors for only a single fish. Organic matter from seagrass meadows is clearly important at the base of food webs for fish on adjacent unvegetated mudflats, either through outwelling of particular organic matter or via a series of predator-prey interactions (trophic relay). Modelling results indicate that saltmarsh grass (Sporobolus) also had high contributions for many fish species, but this is probably a spurious result, reflecting the similarity in isotope values of this autotroph to seagrass. Carbon from adjacent habitats and not in situ microphytobenthos dominates the nutrition for this suite of 22 fishes caught over mudflats. The ultimate autotrophic sources supporting production of three commercially important fish species from Moreton Bay were re-examined by further analysing carbon and nitrogen stable isotope data. Mean isotope values over the whole estuary for fish and autotroph sources were again modelled to indicate feasible combinations of sources. Variability in isotope values among nine locations (separated by 3-10 km) was then used as a further test of the likelihood that sources were involved in fish nutrition. A positive spatial correlation between isotope values of a fish species and an autotroph indicates a substantial contribution from the autotroph. Spatial correlations were tested with a newly developed randomisation procedure using differences between fish and autotroph values at each location, based on carbon and nitrogen isotopes combined in two-dimensional space. Both whole estuary modelling and spatial analysis showed that seagrass, epiphytic algae and particulate organic matter in the water column, potentially including phytoplankton, are likely contributors to bream (Acanthopagrus australis) nutrition. However, spatial analysis also showed that mangroves were involved (up to 33% contribution), despite a very low contribution based on whole estuary modelling. Spatial analysis for sand whiting (Sillago ciliata) demonstrated the importance of two sources, mangroves and microalgae on the mudflats, considered unimportant based on whole estuary modelling. No spatial correlations were found between winter whiting (Sillago maculata) and autotrophs, either because fish moved among locations or relied on different autotrophs at different locations. Spatial correlations between consumer and source isotope values provide a useful analytical tool for identifying the role of autotrophs in foodwebs, and were used here to demonstrate that organic matter from adjacent habitats, and in some cases also in situ production of microalgae, were important to fish over mudflats. Whilst recognising that production from several habitats is implicated in the nutrition of fishes over mudflats in Moreton Bay, clearly the major source is from seagrass meadows. Organic matter deriving from seagrass itself and/or algae epiphytic on seagrass is the most important source at the base of fisheries food webs in Moreton Bay. The importance of seagrass and its epiphytic algae to production of fisheries species in Moreton Bay reinforces the need to conserve and protect seagrass meadows from adverse anthropogenic influences.

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