Zoology - Theses
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ItemEffects of transient copper pollution events on the ecology of marine epifaunal assemblages(University of Melbourne, 2001)Bays and estuaries are subject to anthropogenic toxic waste inputs from many sources and heavy metals are common constituents of that waste. Many toxicant inputs are discrete in time and patchy in space (e.g. spills, urban runoff and periodic discharges) and assemblages may be subject to repeated transient disturbances. I employed a field-dosing technique in many small-scale manipulative studies to assess the impacts of transient copper pollution events on hard-substrate marine invertebrate assemblages. I manipulated the timing, frequency and intensity of transient copper pollution events, factors which have been found to be important determinants of the impact of non-chemical disturbances. Short-term studies of the effect of copper pulses on the initial colonisation of hard substrates in temperate Port Philip Bay revealed direct negative toxicities of the chemical on the recruitment of invertebrates from many phyla including barnacles, serpulids and bryozoans. Field measurements of the copper dose demonstrated that impacts were correlated with the highest concentrations of copper. As concentrations rapidly diminished, many impacts were obscured by high juvenile mortalities or large settlement events. In sub-tropical Hong Kong, recruitment rates and growth were high, especially for the ubiquitous fouling serpulid Hydroides elegans. Within two weeks, this organism was limiting settlement of its own kind and copper pulse impacts were manifest as a shift downwards in the size of recruits close to the copper source. Recovery was also rapid in this assemblage and in both climates, transient pulses that occurred in the initial weeks of longer-term experiments had no lasting effects on assemblage composition. In longer term studies, pulse copper pollution events dramatically altered the assemblages at all sites and times causing a direct reduction in the densities of large space-occupying solitary ascidians. In response to this removal of the dominant ascidians, there were increases in recruitment of many different phyla, and in the abundance of older individuals of some serpulid and bryozoan taxa. In particular, organisms known to be good colonisers but poor competitors for space such as serpulid polychaetes, generally occurred in densities an order of magnitude higher on plates exposed to copper pulses. This was considered to be a density- mediated indirect effect of the toxicant. Experiments on the effects of copper pulses on serpulid densities in the absence of competition for space from other recruits, confirmed this interpretation. The impact of transient pollution events persisted for some time after the agent of disturbance was removed. For the most part, the effects of a single 2-day pulse copper pollution event on an established (8-week old) assemblage had a press effect on community structure that was still evident a further 8 weeks after it had occurred. If a pulse pollution event had a negative effect on an organism�s density, then increasing the intensity or the frequency of that pollution event accentuated that negative effect. If a pulse pollution event had a positive effect on an organism�s density then increasing the intensity or the frequency accentuated the positive effect.