Taphonomy is the study of the fate of information in the fossil record. Information can be lost through the partial or complete destruction of fossils, or through the disruption of their original spatial relationships. Information can be "gained" if the alteration of fossils allows environmental information to be retrieved. In Bahia la Choya, northern Gulf of California, bioerosion, dissolution/maceration, and abrasion produce distinctive textures on the surfaces of shells in intertidal and shallow subtidal environments. Shells from different environments possess different surface textures, suggesting that textures on fossil shells could serve as paleoenvironmental indicators. Algal bioerosion is the chief mode of shell alteration and destruction in Bahia la Choya, though dissolution/maceration and abrasion are locally important. Algal bioerosion of shell surfaces is accelerated by the grazing activity of snails, and is most intense where snails are abundant. Microstratigraphic resolution is limited by vertical mixing of fossils and by the reworking of older fossils into younger deposits. Stratigraphic disorder is the departure from perfect chronological order of fossils in a stratigraphic sequence. I simulated mixing and reworking of fossils by simple computer models, and measured stratigraphic disorder using rank correlation statistics. As modeled, mixing produces disorder slowly, and its effects can be minimized by increasing sample size at each horizon and by increasing the vertical spacing between sampled horizons (though this reduces vertical resolution). Reworking generates disorder more efficiently, and its effects are not reduced by increasing sample size or spacing. The generation of stratigraphic disorder in fossiliferous sediments can also be modeled using M (depth of vertical mixing), I (thickness of sedimentary increments), and L (taphonomic loss rate) as parameters. Increasing M increases the disorder generated, and increasing I and L decreases disorder. For a worst case--high M and low I and L--the vertical spacing between samples must at least 3 times M to ensure a 5% temporal overlap between adjacent samples. A 1% temporal overlap requires a vertical spacing of 4.6 times M.

Density, species diversity, species richness, and evenness of bivalve mollusks were measured in the deep (0.2km to 3.7km) northern Gulf of Mexico to describe the community structure of benthic bivalve mollusks. Density decreased gradually from shallow continental slope depths, with remarkably high values in the Mississippi canyon, to the deepest sites. Diversity of bivalve mollusks increased from shallow continental slope depths, with low values in the Mississippi canyon, to a maximum at intermediate depths (1-2km), followed by a decrease down to the deepest locations (3.7km). Nine distinct groups were formed on the basis of the similarity in species composition. The pattern varied more abruptly on the slope compared to the deeper depths, possibly due to steeper gradients in physical variables. ANOVA indicated that the density of bivalve mollusks was not significantly different at different depths, was not significantly different on different transects, was not significantly different between basin and non-basin, but was significantly different in canyon and non-canyon locations. Similar distinctions were observed in diversity, except that basins were lower than non-basins. The patterns observed reflect the intense elevated input of terrigenous sediments accompanied by high surface-water plankton production from the Mississippi River to the north central gulf.

No description available.

Density, species diversity, species richness, and evenness of bivalve mollusks were measured in the deep (0.2km to 3.7km) northern Gulf of Mexico to describe the community structure of benthic bivalve mollusks. Density decreased gradually from shallow continental slope depths, with remarkably high values in the Mississippi canyon, to the deepest sites. Diversity of bivalve mollusks increased from shallow continental slope depths, with low values in the Mississippi canyon, to a maximum at intermediate depths (1-2km), followed by a decrease down to the deepest locations (3.7km). Nine distinct groups were formed on the basis of the similarity in species composition. The pattern varied more abruptly on the slope compared to the deeper depths, possibly due to steeper gradients in physical variables. ANOVA indicated that the density of bivalve mollusks was not significantly different at different depths, was not significantly different on different transects, was not significantly different between basin and non-basin, but was significantly different in canyon and non-canyon locations. Similar distinctions were observed in diversity, except that basins were lower than non-basins. The patterns observed reflect the intense elevated input of terrigenous sediments accompanied by high surface-water plankton production from the Mississippi River to the north central gulf.

A considerable number of littoral and shallow water marine molluscs from the West Indian region and other areas reached Europe during the second half of the eighteenth and first half of the nineteenth century. These were, in many cases, brought by travelers and navigators and later described by European naturalists. Outstanding among these were Jean B. Lamarck, Carl von Linnaeus, J. F. Gmelin and Alcide d'Orbigny. Although they reported many species from the Lesser Antilles, very few are recorded from Barbados. [...]

This study investigated the physiological ecology, larval biology and population genetics of the nudibranch molluscs Adalaria proxima (A & H) and Onchidoris muricata (Müller). These two species are annual, simultaneous hermaphrodites and are ecologically very similar with the exception that A. proxima reproduces by means of pelagic lecithotrophic larvae whereas Omuricata has long-term planktotrophic larvae. The aim of the study was therefore to determine the selective pressures which resulted in the evolution of different larval types in these two species, and to ascertain the ecological and population genetic consequences thereof. Simple energy budgets comprising the major components (consumption, growth, respiration and reproduction) were constructed for laboratory populations of each species. In both A. proxima and O. muricata, feeding rate displayed an asymptotic increase with body size. Mean feeding rates of A. proxima were greater than those of comparable O. muricata individuals, and overall assimilation efficiency was higher in A. proxima than in O. muricata. This difference was reflected in the somatic growth rates which were correspondingly greater in A. proxima than in O. muricata. Net growth efficiencies were broadly comparable between the two species, however, growth of A. proxima was approximately linear over' time whilst that of O. muricata displayed a curvilinear, almost exponential, pattern. This is interpreted as demonstrating that some form of constraint (possibly feeding rate) operated on the growth rates of A. proxima but not on those of O. muricata. Respiration rates were found to be relatively constant within given animals, but significant differences were found between individuals. The allometry of respiration rate was not constant; Omuricata demonstrated a more rapid increase in respiration rate with increasing body size than did A. proxima. Individual variations in respiration rate did not reflect variations in the energy partitioned to either growth or reproduction. Reproductive patterns in the two species were dissimilar. A. proxima laid fewer spawn masses containing fewer, larger ova than those laid by O. muricata individuals. In addition, the spawning period of A. proxima was shorter than that of O. muricata (60 days and 105 days respectively). Both species exhibited a similar (proportional) degree of somatic catabolism over these periods. The consequently more rapid "degrowth" of A. proxima is interpreted as the necessary utilization of an energy resource (i. e. the soma) caused by an inability to meet the energy demands of reproduction through feeding alone. This was not the case in Oanuricata individuals which exhibited a much smaller maximum body size and were able to feed at a sufficiently rapid rate to maintain reproduction. In the latter case, the longer reproductive period served to maximise the total reproductive output. Several different measures of "Reproductive Effort" (RE) were calculated. These generally indicated that the RE of Omuricata was considerably greater than that of A. proxima. Although such differences have been used in the literature to classify the respective costs of different larval types or "reproductive strategies", the variability of the RE's obtained from the different measures used here has led to the suggestion that the general lack of association between RE and reproductive strategy which has been reported elsewhere may (partially) be attributable to the different measures of RE employed in different studies. Studies of the embryonic and larval period showed that the egg-to-juvenile period of O. muricata was approximately 50% longer than that of A. proxima. This difference was primarily attributable to the extended pelagic development of O. muricata larvae. Estimates of the degree of dispersal, and hence gene-flow, between populations of these species were tested by investigating the biochemical genetics of such populations. No data were available for O. muricata, but A. proxima populations proved to be more genetically heterogeneous than had been expected. It is therefore concluded that actual pelagic dispersal may be considerably abbreviated over that expected on the basis of larval culture data alone. A model is developed to explain the possible consequences of different egg-to-juvenile periods (which accrue from different larval types) on both the ecology of the benthic adult, and on overall energy partitioning to reproduction. However, although (probable) proximate causes and effects of the different reproductive traits exhibited by A. proxima and Oanuricata are shown, it has not been possible to determine the exact selective pressures which caused A. proxima to diverge from the ancestral "O. muricata" stock through the evolution of a pelagic lecithotrophic larva.

Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Plant and Pest Science, 2004? / "August 2003." Includes bibliographical references (leaves 294-333).

Thesis (Ph.D. (Chemistry)) - Rhodes University, 2008.

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references (p. 223-227).

Thesis (M.Sc.) - Carleton University, 2008. / Includes bibliographical references (p. 95-106). Also available in electronic format on the Internet.