Zoology - Theses
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ItemDecapod crustacean diversity along Australia's western continental margin( 2011)A challenge for biodiversity conservation on continental margins is the lack of information on species distributions. Australia has an expansive continental margin that is largely unexplored. To protect and manage biodiversity in Australia’s deep marine environments, biological and abiotic surrogates have been used to classify biodiversity. The aim of this thesis is to describe patterns of decapod diversity on an extensive continental margin and investigate the ability of physical and biological surrogates to represent underlying diversity patterns. The description of biological patterns at large spatial scales requires reliable taxonomic identifications, and consequently a substantial part of the thesis is taxonomic in nature. Surveys of Australia’s western continental margin (~100 to 1000 m depths) were undertaken in 2005 and 2007 by CSIRO Marine and Atmospheric Research in conjunction with museum taxonomists. Species identified from the north-west margin (survey SS05/2007) are reported here and the results of both surveys are summarised. In total, 890 provisional species of decapod crustaceans were discovered during the two surveys, of which 30% are new to science. Many of the species collected and identified (327 or 37%) are known to occur elsewhere, from the tropical Indian Ocean to the West Pacific, and 142 species were recorded in Australia for the first time. A small component of the new fauna discovered during the surveys is described here. These include two new species of the hippolytid shrimp genus Lebbeus and six new species of squat lobster of the family Chirostylidae. Although 45 species of Lebbeus exist worldwide, only one had previously been described from Australia. Squat lobsters including those of the family Chirostylidae are rapidly advancing our understanding of deep-sea environments across broad spatial scales and therefore the taxonomy and distribution of these animals is a research priority. In addition to the six new species described, seven new records of Indo-West Pacific species are reported for Australia. This study increases the number of chirostylid species in Australia from 40 to 53. Keys to Australian species of the genera Gastroptychus, Uroptychodes and Uroptychus are provided. The distributional records of decapods along the margin were used to determine the relative importance of environmental and spatial predictor variables on both species richness (alpha diversity) and species turnover. The best predictors of species turnover were temperature, oxygen and salinity, factors that reflect the oceanographic features that dominate distinct depth bathomes along the slope. On both the shelf and the upper slope, I differentiated an assemblage north of 22°S from another south of 23°S in the vicinity of North-west Cape. This location correlates with changes in oxygen concentration along the margin and marks the head of the Leeuwin Current system. The number of species within samples was highly variable, but a small significant increase in diversity towards the tropics was evident. On the shelf edge (~100 m) temperature was correlated with latitude, oxygen and salinity, and thus the independent effects of each variable could not be separated. On the shallow upper slope (~400 m) temperature was disassociated from latitude, and latitude proved to be the best predictor of sample species richness. The predictive power of latitude over other variables indicates that proximity to the highly diverse Indo-West Pacific is important. Management of both terrestrial and marine environments often uses vertebrates as a surrogate for the diversity of the overall fauna, as their distributions are better documented than those of most invertebrates. In the case of Australia’s deep-water marine planning, the distributions of fishes were used to classify bioregions. To ensure this classification represents underlying biodiversity, the spatial patterns of fishes with three invertebrate taxa were compared along a latitudinal gradient. Changes in community structure along the margin were broadly congruent for fishes and all invertebrate taxa. In contrast, broad-scale species richness patterns differed between major taxa, leading to the conclusion that one taxonomic group cannot be taken to represent others in terms of species richness or taxonomic distinctness. The results of this thesis lend support to Australia’s marine planning framework in which bioregions are defined according to the distributions of fishes and major oceanographic features. As in other large-scale studies which seek to examine the drivers of diversity in the deep sea, attributing causal relationships is difficult as many covariates are correlated. However, it was possible to distinguish some variables which have greater explanatory power than others. Future research will invariably consider the distributions of fauna over much larger scales as biological and environmental datasets are assembled at global scales, and this may help to explain the physical and historical constraints of deep-sea distributions.
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ItemPatterns in the distribution and abundance of reef fishes in South Eastern Australia( 2011)This research investigated patterns in the distribution and abundance of nearshore fishes of south-eastern Australia. I used two methods to survey fishes, underwater visual census (UVC) and baited remote underwater video (BRUV). A comparison between these methods revealed that BRUV recorded higher relative abundance of mobile predators, while UVC observed higher relative abundance of herbivores, territorial species, and small site-attached species. These results suggest that studies surveying diversity would do best to employ multiple methods. In cases where funds are limited, UVC may provide a more complete estimate of diversity than BRUV as UVC recorded higher diversity, species richness and more individuals. Combining measures of abundance with habitat data, I investigated fish-habitat associations, specifically exploring how altering spatial grain influenced the strength of correlations between fish and habitat. Species of different sizes responded to habitat measured over different scales, with large-bodied species only displaying strong correlations with habitat when it was measured over large scales. These results suggest that research quantifying fish-habitat associations needs to take spatial grain into account. In addition, many species may respond to changes in habitat at scales larger than are typically investigated. Understanding not only how species interact with their environment but also the scale at which these associations occur is essential for management and conservation. I investigated biogeographic patterns in the distribution of fishes in Victoria using abundance measured by BRUV and UVC. The BRUV data displayed a cline in change across the state in which dissimilarities between locations were linearly related to distance. In contrast, data collected using UVC indicated the presence of a large faunal break in the vicinity of Ninety Mile Beach, and a second break between Cape Conran and Cape Howe, suggesting that contemporary habitat discontinuity, flow and/or temperature may be important factors structuring communities in this region. At a still larger scale, I explored relationships at upper and lower bounds between body size, geographic range size and abundance using data collected from Australia and New Zealand. At maxima, the relationship between body size and abundance was negative but steeper than expected, possibly driven by diver-averse behaviour of large species. At minima, body size and geographic range size were positively related, implying that body size determines the minimum area that a species must occupy. In contrast, at the upper bound this relationship was negative for non-perciform fishes, a K-selected group whose geographic range size could be constrained by their limited dispersal capacity. Distribution-abundance relationships deviated from predictions, with a negative relationship at the upper bound for Perciformes, which could be driven by the high dispersal potential of widespread species that results in diffuse low-density populations. From these results, I concluded, first, that fishes appear to differ from terrestrial taxa, which may be attributed in part to large-bodied fishes’ limited capacity for dispersal. Second, the approach of applying regressions to maxima and minima uncovered relationships that would have been obscured had they been investigated at the mean, highlighting the importance of exploring limits in macroecological relationships.