Zoology - Theses

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    The ecological role of canopy-forming fucoid algae on temperate intertidal rocky shores
    Pocklington, Jacqueline Brooke. (University of Melbourne, 2012)
    Understanding the role species play in ecosystems is vital to understanding how ecosystems function. Increasing anthropogenic and natural disturbance to coasts including the influence of climate change has highlighted the need to understand the function of species, especially those that cover large geographic ranges and dominate available space. Canopy-forming algae and seagrasses have been shown to provide habitat for associated species in subtidal environments through the provision of substrate for colonisation by algae and invertebrates; and the environmental conditions they modify through their structure, such as available light, and water flow. Studies on canopy-forming algae on rocky intertidal shores in Europe, Northern America and New Zealand have found evidence for an ecosystem engineering role, though until now this has been untested on Australian shores. Examination of species associations with the canopy-forming alga Hormosira banksii along Victorian rocky shores found differences in species assemblage occur in comparison to areas of shore where canopy is absent, adding to the overall reef biodiversity. Subsequent experimental investigation tested the ecological function of H. banksii and found that canopy-cover alters the species� ability to modify environmental conditions including temperature and light intensity, and as a consequence the species that can associate with the alga. The ecological role of the northern hemisphere fucoid alga Ascophyllum nodosum was also experimentally investigated to test the consequence of a loss of canopy biomass. Destruction of the A. nodosum canopy that reduces its cover over the underlying substratum was found to reduce the ability of the canopy to modify environmental conditions and as a consequence the species assemblage that are associated with intact A. nodosum canopy. Partial thinning of no more than 50% of the fronds arising from the holdfasts didn�t alter species assemblages or the physical conditions measured in comparison to controls indicating resilience to this level of disturbance. The function of intact canopy-forming algae was correlated with measures of substratum rugosity and the presence of abiotic microhabitats on the shores studied. The abundances of some macroinvertebrates were found to vary in relation to indices of substratum complexity, although this was idiosyncratic through time. Macroinvertebrates occupied a range of microhabitats available on the shore. Species strongly associated with the canopy were most often found to occupy canopy-dependant microhabitats such as holdfasts and fronds. But neither of these factors altered the function of the canopy algae as an ecosystem engineer. The results of this thesis allow prediction of the consequences of damage to intertidal canopy algae (ecosystem engineers). Both Hormosira banksii and Ascophyllum nodosum may be monitored and managed as a surrogate for shore biodiversity.
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    Fish responses to seagrass habitat fragmentation
    Macreadie, Peter Ian. (University of Melbourne, 2009)
    Marine organisms that inhabit coastal waters increasingly have to deal with habitat fragmentation and concomitant increases in edge habitat. Effective conservation of coastal habitats requires an understanding of how and why organisms respond to these habitat changes. Seagrass is a critical marine habitat that is becoming increasingly fragmented. To understand how fish living in seagrass respond to fragmentation, I actively fragmented artificial seagrass habitats (single, continuous 9 m2 patches fragmented to 4 discrete 1 m2 patches) and evaluated changes in fish abundance. Total fish abundance was unaffected by fragmentation, and this was consistent through time (1 day, 1 week, 1 month). If fish crowded into remnant seagrass fragments, then crowding effects may explain the lack of decline in fish abundance that would otherwise be expected from seagrass habitat loss. Progressive removal of seagrass (16 m2 patches to 4 m2) showed that fish temporarily (?1 day) crowd into remnant patches, but crowding effects could not explain the longer-term persistence of fish in fragmented seagrass. I then tested the hypothesis that fish are more abundant at seagrass edges than interiors (i.e. �positive edge effects�) and that the effects of seagrass habitat loss on fish abundance were offset by an increase (25%) in edge habitat in fragmented patches. I found that fish were 3 times more abundant at edges than interiors in continuous seagrass (single, 9 m2 patches), but in patchy seagrass (4 discrete 1 m2 patches) there was no difference, which is probably because pipefish perceived patchy seagrass as consisted entirely of �edge� habitat. To test whether the observed edge effects in continuous seagrass were caused by increased availability of food at edges, I estimated the abundance of food across continuous seagrass patches. Food abundance peaked at seagrass edges and was 16% higher than samples taken from patch interiors. To separate causality from correlation, I supplemented interiors of continuous seagrass with food and found that edge effects ceased, which indicated that fish were moving from patch edges to interiors in response to food supplementation. This provided evidence that fish were more abundant at seagrass edges due to greater food availability.
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    Altitudinal distribution of two invasive leafminers, Liriomyza huidobrensis (Blanchard) and L. sativae Blanchard (Diptera: Agromyzidae) in Indonesia
    Warsito. (University of Melbourne, 2008)
    My thesis assessed the altitudinal distribution of two invasive leafminers., L. huidobrensis and L. sativae (Diptera: Agromyzidae), and examined the extent of environmental factors influencing their distribution. It has been well known based on studies conducted in laboratory that both species have different response to particularly temperature and host, but no study has been conducted to assess impacts of both factors and others in influencing altitudinal colonization patterns. A comprehensive survey was undertaken in the mountainous area of Dieng, the province of Central Java, Indonesia by collecting infested leaves, trapping adults, mapping habitat composition and recording the temperature. This study revealed that the distribution of both species differed with altitudes. Liriomyza sativae were only found and dominated at low altitudes, where L. huidobrensis were found across the entire gradient and dominated at high altitudes. Hosts did not limit the distribution of both species, but it may have had indirect effects on the dominance of L. huidobrensis. At high altitudes where the host faba beans preferred by this species were common, L. huidobrensis dominated, whereas at low altitude where less preferred hosts such as cucumber and long bean were common, L. huidobrensis was less common than L. sativae. The survey and the field experiment indicate that temperature may have limited the distribution of L. sativae because this species was absent where temperatures occasionally fell below 10�C. However, temperature did not limit the distribution of L. huidobrensis. This is consistent with a population growth model using only temperature as an explanatory factor. A comprehensive survey also indicated that there was no evidence of parasitoids limiting leafminer distributions. Parasitoids were found at all altitudes where leafminers were present Twelve parasitoids were identified which fell into three families Asecodes delucchii (Boucek), A. erxias (Walker), Chrysocharis sp., Cirrospilus ambiguus Hansson & LaSalle, Closterocerus sp., Hemiptarsenus varicornis (Girault), Neochrysocharis beasleyi Fisher & La Salle, N. formosa (Westwood), N. okazakii (Kamijo), and Quadrastichus liriomyzae Hansson & LaSalle are from the Eulophidae family, Gronotoma micromorpha (Perkins) is from the Eucolidae family, and Opius chromatomyiae Belokobylskij & Wharton is from the Braconidae family. Diversity of parasitoid declined with altitude and was negatively associated with percentage of parasitism, which increased with altitude. My study also investigated changes of morphological characters along the altitudinal gradient. Morphology only changes with altitude in L. huidobrensis, and this appeared to be driven both by genetic and environmental factors. The morphological changes may reflect adaptation to climatic conditions across the altitudinal gradient. Competitive interactions were considered in the laboratory and in the field. My study revealed that competition only occurred in laboratory where intraspecific competition was stronger than interspecific competition, although the latter was also detected. Intraspecific competition gave an advantage for rare species whereas in interspecific interactions there was no advantage to any one species. In the field experiments, there was no evidence of competition between both species because densities of leafminers were low. In field surveys the densities of leafminers were also usually low, suggesting that in field populations competition might be uncommon and have little impact on the altitudinal distribution of the species.
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    The role of the peptide hormone relaxin in cardiac fibrosis
    McGuane, Jonathan T. (University of Melbourne, 2007)
    Relaxin is a peptide hormone primarily synthesised in the corpus luteum during pregnancy, with a range of actions related to functional modifications of the reproductive tissues and parturition. Relaxin is transported via the circulation to its target tissues, where it is thought to stimulate physiological effects through the activation of a high-affinity G protein-coupled receptor (LGR7). In the heart, these effects may include modulation of the quantity and composition of the extracellular matrix (ECM), the network of macromolecules that provides structural and functional support to the myocardium. A number of factors play an important role in the regulation of the ECM, including ECM components themselves (such as fibrillar collagen) and ECM-degrading enzymes known as matrix metalloproteinases (MMPs). This thesis examined the role of relaxin in the regulation of these factors using a novel animal model, the relaxin-deficient (Rlx-l-) mouse. Previous work has shown that aged male Rlx-l- mice develop ventricular fibrosis (ECM accumulation) as a result of increased collagen expression, a phenotype that increases in severity with advancing age (Du, Samuel et al. 2003). These and other findings led to the suggestion that relaxin has anti-fibrotic properties in vivo. The Rlx-l- mouse model was used to further examine the role of this peptide in the regulation of the cardiac ECM. Initial studies in 2 - 8 month-old male mice demonstrated that relaxin deficiency does not cause increased collagen mRNA synthesis or excessive collagen deposition in the ventricular myocardium. Furthermore, there was no influence of relaxin on the expression of MMPs. In the cervix of pregnant mice (a well-known target tissue for the hormone), however, relaxin deficiency resulted in marked upregulation of several MMPs. The effect of relaxin treatment in vivo was then tested by chronic administration of the hormone to male Rlx-l- mice. Seven month-old mice, but not twelve month-old mice, responded to treatment with an upregulation in the synthesis of not only MMP (in accordance with the classic anti-fibrotic actions of the hormone) but also collagen genes in the ventricles, suggestive of a positive feedback mechanism activated by ECM degradation. This study demonstrated for the first time that relaxin concurrently stimulates both MMP and collagen gene expression in the heart, indicating that the anti-fibrotic effects of this hormone may not be as clear-cut as previously thought. In this thesis it was also demonstrated that LGR7 but not relaxin is expressed in the mouse heart. These data may explain why exogenous relaxin was able to induce effects in the heart, because there are LGR7 receptors present. In contrast, as there is no relaxin ligand expression in the heart, this may explain why relaxin deficiency did not influence gene expression or collagen deposition. Interestingly, two other novel relaxin-like ligand/receptors pairs were also identified as being expressed in cardiac tissues: relaxin-3/GPCR135 and Insl5/GPCR142. The functions of these ligands/receptors await further study. In summary, this thesis has contributed to the understanding of the role and potential mechanisms of action of both endogenous and exogenous relaxin in the mouse heart, and has clarified the relevant components of the paracrine cardiac relaxin system.
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    The ecology and song of the duetting Eastern whipbird (Phosphodes olivaceus)
    Rogers, Amy Catherine. (University of Melbourne, 2005)
    In this thesis I investigate the function of antiphonal duets, using as my model system the Australian eastern whipbird, Psophodes olivaceus. Fieldwork was carried out between 2000- 2003 on a colour-banded population of eastern whipbirds at Mimosa Rocks National Park, near Tathra, NSW. Eastern whipbirds form stable, long-term, socially monogamous pair bonds with a low rate of pair divorce. Males and females show sex role convergence in parental care and territory defence. While only females build the nest and incubate, both sexes feed offspring at the nest, with males feeding nestlings at a higher rate than females. On fledgling the brood of two is divided and each parent cares exclusively for one fledging during an extended period of post-fledging care. Males and females together defend an exclusive territory throughout the year. Competition for territories at this site is intense, due to a high rate of adult survival, limited dispersal by offspring and an extremely low rate of territory turnaround, despite the presence of numerous unpaired adult 'floaters'. Intra-sexual competition between females appears to be particularly strong given that sex ratios from nestling through to unpaired adult stages are female-biased. Eastern whipbird males and females coordinate their songs to form precise duets that are initiated exclusively by the male. Males and females each possess a repertoire of different song types, which are combined non-randomly to form specific duet types. Females produce two types of song: response songs, which are mainly used in the context of a duet, and 'type n' songs which are used only as solo songs. Both sexes share most of their songs with same-sex neighbours and the repertoire of song types appears to play an important role in allowing song type-matching during territorial interactions with intruders. Playback experiments suggest that the sexes differ in the extent to which they are influenced by the song types of rivals and partners during interactions. Males matched most of their songs with the song type broadcast by the speaker during simulated intrusion by male rivals. Females, in contrast, always fitted the song types of their partners rather than matching the songs of female rivals. By replying to their partner, females may be signalling their commitment to the pair bond, or demonstrating their own, or their partners, paired status to female rivals. Further playback experiments confirmed that females showed a more aggressive response to simulated intrusion by female rivals than male rivals, and answered a higher proportion of their partner's songs to form duets in the presence of a same-sex rival. Female eastern whipbirds therefore appear to reply to their partners in order to defend their exclusive position within the partnership. This behaviour appears to be the consequence of high intra-sexual competition between females for mates, coupled with high benefits associated with maintaining exclusive access to male care. The high level of intra-specific competition between females also seems to have led to the development of a novel vocal strategy in the eastern whipbird. Females not only replied to their partners but also to male intruders to form precise extra-pair duets which were similar in structure to pair duets. Simulated intrusions suggested that the rate of extra-pair duets produced was highest in the presence of a female rival. Thus, females may respond to males other than their partners as a means of type-matching and overlapping the songs of female rivals.
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    A molecular analysis of bryozoan dispersal
    Mackie, Joshua A. (University of Melbourne, 2002)
    Cheilostome bryozoans disperse primarily via short-lived, non-feeding larvae. Shiphull fouling is the likely cause of recent introductions of some species. Patterns of genetic diversity of three invasive bryozoans were compared to determine the effects of modem range expansion on genetic structure. The influence of natural dispersal mechanisms and local geological factors was assessed in studies of the genetic variation of two bryozoans that occur naturally in south-eastern Australia. Mitochondrial COI gene sequences of 388-429 base pairs in length were compared for each species. In addition, an experiment was conducted to determine whether bryozoans and other organisms within a marina show different microscale recruitment responses in the presence of 'antifouling' paints used to prevent the settlement of marine organisms. The occurrence of high-tolerance responses in introduced populations could indicate effects of selection associated with hull-fouling. The three introduced species showed contrasting levels of mitochondrial nucleotide diversity. Bugula neritina occurred throughout temperate and tropical oceans at the time of first taxonomic records. Globally widespread sampling revealed a single cosmopolitan species with no detected COI nucleotide variation. This finding contrasts with previously reported COI evidence of multiple divergent cryptic species of B. neritina on the American coastline. Minimal sequence diversity was found in the introduced gene pool of Watersipora subtorquata, an Atlantic bryozoan that has recently colonised the Pacific (?30 = 0.0016). The genetic homogeneity suggests expansions of B. neritina and W. subtorquata originate from a single population source. Comparison of introduced populations of Watersipora arcuata, a bryozoan that has recently colonised Australia, Hawaii and other coastlines from an Eastern Pacific source, revealed comparatively high nucleotide diversity (?51 = 0.0221), suggesting range expansion originated from multiple ancestral isolates. Sequences demonstrated that the range of Bugula dentata, a species that occurs widely on tropical and subtropical reefs, consists of a complex of divergent species that formed during the Miocene. A shallow area of epicontinental shelf underlying the Bass Strait sea zone between Victoria and Tasmania has been periodically exposed as a result of Quaternary glacioeustatic fluctuation. Genetic diversity in south-eastern Australian marine species is potentially affected by isolation across the temporary land bridge and the pattern of interglacial recolonisation of Bass Strait. Populations of B. dentata, sampled at four areas in south-eastern Australia, had a shallow phylogeographic structure (?16= 0.003, Fst = 1.0), suggesting post-Pleistocene recolonisation from a single refuge zone. Mucropetraliella ellerii, a bryozoan that is endemic to the inner south-eastern Australian shelf, was shown to have high nucleotide diversity across its range (?53 =0.0724). Populations in southern and eastern Australia were separated by a net sequence divergence of 10.9% (K2P-corrected), suggesting a long-term (Miocene-Pliocene age) population break. Analysis of the demographic signal present within the sequence samples provided evidence of contrasting genetic effects related to recolonisation. Differences in sequence diversity of each of the two major M. ellerii isolates may be related to the area of continental shelf that houses refuge populations for recolonisation. In the marina experiment, a copper oxide and a Tributyltin (TBT)-based antifouling paint were used to create ion diffusions around settlement plates. Differences in the density of recruitment of different species among three treatments (control, copper and blank) were measured to test the hypothesis that introduced populations of shiphull fouling species have a higher chemical tolerance than non-introduced species. There was one substantive effect. Chemical treatments reduced densities of a native bryozoan Celloporaria nodulosa, whereas the introduced species Watersipora subtorquata showed a high tolerance of the effects of chemicals, increasing in density on plates surrounded by copper antifouling paint. The bryozoan fouling response thus exhibits species-level variance that is relevant to mechanisms of introduction and may prove to be a useful trait for studying how adaptation and population dynamics are linked.
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    The ecology and song of the duetting Eastern whipbird (Phosphodes olivaceus)
    Rogers, Amy Catherine. (University of Melbourne, 2005)
    In this thesis I investigate the function of antiphonal duets, using as my model system the Australian eastern whipbird, Psophodes olivaceus. Fieldwork was carried out between 2000- 2003 on a colour-banded population of eastern whipbirds at Mimosa Rocks National Park, near Tathra, NSW. Eastern whipbirds form stable, long-term, socially monogamous pair bonds with a low rate of pair divorce. Males and females show sex role convergence in parental care and territory defence. While only females build the nest and incubate, both sexes feed offspring at the nest, with males feeding nestlings at a higher rate than females. On fledgling the brood of two is divided and each parent cares exclusively for one fledging during an extended period of post-fledging care. Males and females together defend an exclusive territory throughout the year. Competition for territories at this site is intense, due to a high rate of adult survival, limited dispersal by offspring and an extremely low rate of territory turnaround, despite the presence of numerous unpaired adult 'floaters'. Intra-sexual competition between females appears to be particularly strong given that sex ratios from nestling through to unpaired adult stages are female-biased. Eastern whipbird males and females coordinate their songs to form precise duets that are initiated exclusively by the male. Males and females each possess a repertoire of different song types, which are combined non-randomly to form specific duet types. Females produce two types of song: response songs, which are mainly used in the context of a duet, and 'type n' songs which are used only as solo songs. Both sexes share most of their songs with same-sex neighbours and the repertoire of song types appears to play an important role in allowing song type-matching during territorial interactions with intruders. Playback experiments suggest that the sexes differ in the extent to which they are influenced by the song types of rivals and partners during interactions. Males matched most of their songs with the song type broadcast by the speaker during simulated intrusion by male rivals. Females, in contrast, always fitted the song types of their partners rather than matching the songs of female rivals. By replying to their partner, females may be signalling their commitment to the pair bond, or demonstrating their own, or their partners, paired status to female rivals. Further playback experiments confirmed that females showed a more aggressive response to simulated intrusion by female rivals than male rivals, and answered a higher proportion of their partner's songs to form duets in the presence of a same-sex rival. Female eastern whipbirds therefore appear to reply to their partners in order to defend their exclusive position within the partnership. This behaviour appears to be the consequence of high intra-sexual competition between females for mates, coupled with high benefits associated with maintaining exclusive access to male care. The high level of intra-specific competition between females also seems to have led to the development of a novel vocal strategy in the eastern whipbird. Females not only replied to their partners but also to male intruders to form precise extra-pair duets which were similar in structure to pair duets. Simulated intrusions suggested that the rate of extra-pair duets produced was highest in the presence of a female rival. Thus, females may respond to males other than their partners as a means of type-matching and overlapping the songs of female rivals.
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    A molecular analysis of bryozoan dispersal
    Mackie, Joshua A. (University of Melbourne, 2002)
    Cheilostome bryozoans disperse primarily via short-lived, non-feeding larvae. Shiphull fouling is the likely cause of recent introductions of some species. Patterns of genetic diversity of three invasive bryozoans were compared to determine the effects of modem range expansion on genetic structure. The influence of natural dispersal mechanisms and local geological factors was assessed in studies of the genetic variation of two bryozoans that occur naturally in south-eastern Australia. Mitochondrial COI gene sequences of 388-429 base pairs in length were compared for each species. In addition, an experiment was conducted to determine whether bryozoans and other organisms within a marina show different microscale recruitment responses in the presence of 'antifouling' paints used to prevent the settlement of marine organisms. The occurrence of high-tolerance responses in introduced populations could indicate effects of selection associated with hull-fouling. The three introduced species showed contrasting levels of mitochondrial nucleotide diversity. Bugula neritina occurred throughout temperate and tropical oceans at the time of first taxonomic records. Globally widespread sampling revealed a single cosmopolitan species with no detected COI nucleotide variation. This finding contrasts with previously reported COI evidence of multiple divergent cryptic species of B. neritina on the American coastline. Minimal sequence diversity was found in the introduced gene pool of Watersipora subtorquata, an Atlantic bryozoan that has recently colonised the Pacific (?30 = 0.0016). The genetic homogeneity suggests expansions of B. neritina and W. subtorquata originate from a single population source. Comparison of introduced populations of Watersipora arcuata, a bryozoan that has recently colonised Australia, Hawaii and other coastlines from an Eastern Pacific source, revealed comparatively high nucleotide diversity (?51 = 0.0221), suggesting range expansion originated from multiple ancestral isolates. Sequences demonstrated that the range of Bugula dentata, a species that occurs widely on tropical and subtropical reefs, consists of a complex of divergent species that formed during the Miocene. A shallow area of epicontinental shelf underlying the Bass Strait sea zone between Victoria and Tasmania has been periodically exposed as a result of Quaternary glacioeustatic fluctuation. Genetic diversity in south-eastern Australian marine species is potentially affected by isolation across the temporary land bridge and the pattern of interglacial recolonisation of Bass Strait. Populations of B. dentata, sampled at four areas in south-eastern Australia, had a shallow phylogeographic structure (?16= 0.003, Fst = 1.0), suggesting post-Pleistocene recolonisation from a single refuge zone. Mucropetraliella ellerii, a bryozoan that is endemic to the inner south-eastern Australian shelf, was shown to have high nucleotide diversity across its range (?53 =0.0724). Populations in southern and eastern Australia were separated by a net sequence divergence of 10.9% (K2P-corrected), suggesting a long-term (Miocene-Pliocene age) population break. Analysis of the demographic signal present within the sequence samples provided evidence of contrasting genetic effects related to recolonisation. Differences in sequence diversity of each of the two major M. ellerii isolates may be related to the area of continental shelf that houses refuge populations for recolonisation. In the marina experiment, a copper oxide and a Tributyltin (TBT)-based antifouling paint were used to create ion diffusions around settlement plates. Differences in the density of recruitment of different species among three treatments (control, copper and blank) were measured to test the hypothesis that introduced populations of shiphull fouling species have a higher chemical tolerance than non-introduced species. There was one substantive effect. Chemical treatments reduced densities of a native bryozoan Celloporaria nodulosa, whereas the introduced species Watersipora subtorquata showed a high tolerance of the effects of chemicals, increasing in density on plates surrounded by copper antifouling paint. The bryozoan fouling response thus exhibits species-level variance that is relevant to mechanisms of introduction and may prove to be a useful trait for studying how adaptation and population dynamics are linked.
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    Effects of transient copper pollution events on the ecology of marine epifaunal assemblages
    Johnston, Emma L. (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.
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    Effects of transient copper pollution events on the ecology of marine epifaunal assemblages
    Johnston, Emma L. (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.