The ecology of Patella

The present thesis is aimed principally at the population dynamics and biological interactions of Patella species. Most of the work is based on all eleven of the South African species, although volume of work necessitated the omission of the less common species from parts of the work. The research has been centred around the juveniles and adults, although it is realised that larval biology is logically the next field which needs to be explored. The thesis is presented as a series of separate papers, the first in published form and the remainder in manuscript, and is concluded by a resume. A single supporting paper is also included. The entire thesis is based on original work by the candidate, except where acknowledged in the text. The more important conclusions are summarised at the end of each section

The ecology of Patella

The present thesis is aimed principally at the population dynamics and biological interactions of Patella species. Most of the work is based on all eleven of the South African species, although volume of work necessitated the omission of the less common species from parts of the work. The research has been centred around the juveniles and adults, although it is realised that larval biology is logically the next field which needs to be explored. The thesis is presented as a series of separate papers, the first in published form and the remainder in manuscript, and is concluded by a resume. A single supporting paper is also included. The entire thesis is based on original work by the candidate, except where acknowledged in the text. The more important conclusions are summarised at the end of each section

Effects of Sediment on the Energy Budgets of Four Scleratinian (Bourne 1900) and Five Alcyonacean (Lamouroux 1816) Corals

The physiological reactions to sediment of four scleractinia and five alcyonacea from South Africa were observed in the laboratory. Species tested were Favia favus Forskal, Favites pentagona Esper, Platygyra daedalea Ellis & Solander, Gyrosmilia interrupta Ehrenberg, Lobophytum depressum Tixier-Durivault,Lobophytum venustum Tixier-Durivault, Sinularia dura (Pratt), Sinularia leptoclados (Ehrenberg) andSarcophyton glaucum (Quoy & Gaimard). Natural sedimentation levels and light conditions were simulated. Photosynthetic carbon production and respiration were measured by respirometry. Loss of fixed carbon through mucus production was measured directly by filtration. The results were used to model daily energy budgets for these species. One set of models allowed for 50% PARs (photosynthetically active radiation at the surface), another set of models allowed for 25% PARs. The models showed severely diminished productivity and decreased respiration under sedimented conditions. Production/respiration () ratios of all species were above 1 in the absence of sediment and dropped below unity when the corals were subjected to sedimentation. Although overall respiration dropped, its demand upon the also diminished amount of photosynthetically produced carbon rose dramatically. Without sediment, mucus output averaged 35% of daily respiration; this rose to 65% when sediment was applied. Sediment affects coral metabolism by decreasing photosynthetic production, increasing relative respiration and increasing carbon-loss through greater mucus output

Disturbance associated with bait-collection for sandprawns (Callianassa kraussi) and mudprawns (Upogebia africana): Long-term effects on the biota of intertidal sandflats

The sandprawn Callianassa kraussi and the mudprawn Upogebia africana are used extensively as fish bait in southern Africa. A holistic analysis of disturbance associated with experimental prawn-collecting was undertaken to determine its repercussions upon the sediment and associated macrofaunal, meiofaunal, microbial and microalgal communities. Patterns of recovery were examined for 18 months following the disturbance. The recovery of both C. kraussi and U. africana was far more protracted than predicted, taking 18 months for completion. Sedimentary compaction, associated with the removal of prawns, could account for these prolonged recoveries. Both C. kraussi and U. africana suffered greater depressions of population densities (ca. 70%) than would have been expected from the proportions removed (ca. 10% and 46% respectively). This suggests that disturbance and sedimentary compaction have greater effects than the removal of sand- and mudprawns per se. One month after the disturbance of C. kraussi, chlorophyll levels increased above control levels and remained elevated for a further 2–3 months. In contrast, the removal of U. africana resulted in nett decreases in chlorophyll levels for approximately one month following the disturbance. A short-lived decline in bacterial numbers was apparent following the removal of C. kraussi but not U. africana. Meiofaunal numbers declined immediately after disturbance of both C. kraussi and U. africana, but this depression was followed by explosive increases and then a return to control levels. The macrofauna was slower to recover and, after initial reductions of numbers, biomass and species richness, still showed signs of depression 18 months after the disturbance. Three response patterns were apparent: species which were immediately reduced by the treatments and were also slow to recover; species which appeared to have their recruitment suppressed relative to the control; and species which were unaffected by the treatment. Only a single macrofaunal species, the hermit crab Diogenes brevirostris, benefited from the disturbance. Similar trends were observed following the harvesting of both C. kraussi and U. africana

Function of Funnel-Shaped Coral Growth in a High-Sedimentation Environment

Advantages and disadvantages of a funnel-shaped growth in 2 coral species (Acropora clathrata, Turbinaria peltata) in a high-sedimentation environment (Natal, South Africa) were observed in the field and modeled in a flow tank. Funnel-shaped growth serves different purposes in different hydrographic settings. In calm waters with little currents (in our case deep reef areas, 18 to 25 m) funnel-shaped colonies served as \u27sacrificial sediment traps\u27: all sediment trapped inside the funnel was directed towards the centre, where it was concentrated. There, tissues underwent necroses, but all other tissues remained sediment free and healthy. In areas with high currents (in our case shallower reef areas with high surge, 8 to 14 m) funnels tended to be self-cleaning. By a process of vortex shedding, mass replacement of fluid within the funnel also led to the removal of all sediment. Current speeds between 30 and 90 cm s-1 were enough to clean the funnels of 3 experimental grain sizes (coarse, fine, medium sand)

Morphological and genetic differentiation of Patella granularis (Gastropoda: Patellidae): recognition of two sibling species along the coast of southern Africa

Morphological and isozyme variations between 13 populations of the species hitherto named Patella granularis were investigated to see whether differences in shell structure between the west coast versus the south and east coasts of southern Africa are supported by other morphological features or by genetic differences. The shells showed a definite decrease in size from west to east, but this is correlated with productivity and is of no diagnostic use in distinguishing between populations. Discriminant functions analysis based on shell morphometrics failed to separate populations from the three coastal regions. Shells from the northern east coast do, however, have shell nodules with a dark pigmentation, distinctly separating them from those further south and west. No differences in radular or soft part morphology were detected between the populations, but the four northernmost populations on the east coast have a significantly shorter Z looping of the gut than the other populations along the coast. Significant microstructural differences in the sperm were also detected between these two groups of populations. Electrophoretic analysis of 16 enzyme loci failed to detect any significant differences between the west and south coast populations, but revealed a genetic identity (Nei) of 0.528 as well as four diagnostic alleles between the four northernmost populations from the east coast compared with those to the south and west. The two genetically distinct forms occurred sympatrically at one of the study sites on the east coast (Coffee Bay). It was concluded the two groupings were sufficiently different to warrant the recognition of a separate species, which is centred in KwaZulu-Natal on the east coast and extends south to Coffee Bay, from where it is replaced by P. granularis. There is, however, no evidence at all that the west coast populations are in any way separable from the remaining populations of P. granularis on the south coast

Comparing community structure on shells of the abalone Haliotis midae and adjacent rock: implications for biodiversity

This paper concerns the effects on biodiversity of depletion 24 of the South African abalone Haliotis midae, which is a long-lived species with a large corrugated shell that provides a habitat for diverse benthic organisms. We compared community structure on H. midae shells with that on adjacent rock at three sites (Cape Point and Danger Point sites A and B), and at two different times of the year at one of these sites. Shells of H. midae consistently supported communities that were distinctly different from those on rock. In particular, three species of non-geniculate (encrusting) corallines, Titanoderma polycephalum, Mesophyllum engelhartii and Spongites discoideus were all found either exclusively or predominantly on shells, whereas another non-geniculate coralline, Heydrichia woelkerlingii, occurred almost exclusively on adjacent rock. The primary rocky substratum, however, supported a higher number of species than abalone shells. Possible reasons for the differences between the two substrata include the relative age, microtopography and hardness of the substrata; the abundance of grazers on them; and the relative age of different zones of the abalone shell, which support communities at different stages of succession. Diversity on shells was lowest in zones that were either very young or very old, in keeping with the intermediate disturbance hypothesis. The distinctiveness of shell epibiota will increase diversity despite having a lower diversity than that of adjacent rock. Decimation of H. midae by overfishing therefore has implications biodiversity conservation.Web of Scienc

Modeling a regime shift in a kelp-forest ecosystem caused by a lobster range expansion

The South African West Coast rock lobster, Jasus lalandii (H. Milne-Edwards, 1837), has expanded its range to the southeast, where its abundance has increased radically. The ecological consequences of this “invasion” are likely to be considerable. We employed a minimally realistic model to simulate the “invasion” and to explore interactions of J. lalandii with the sea urchin, Parechinus angulosus (Leske, 1778), and the abalone, Haliotis midae Linnaeus, 1758, juveniles of which shelter beneath this urchin. Model fits to empirical data were good, although species-interaction terms were difficult to estimate. Base-case trajectories indicated: (1) Lobster biomass peaked at about 1000 t in 1994 and was then reduced by fishing to a stable value approximately 50% lower by 2008. (2) Urchins remained close to carrying capacity in “noninvaded” areas but collapsed to local extinction by 1997 in the invaded area. (3) Abalone declined over 2000–2008 in noninvaded areas because of illegal fishing and collapsed to near zero in the “invaded” area because of illegal fishing combined with increased lobster abundance. Sensitivity analyses favored the hypothesis that the invasion was due to adult immigration rather than larval recruitment. Modeled 50-yr projections indicated that urchins will remain locally extinct in the invaded area, even 50 yrs into the future. The abalone collapse in the invaded area would persist >50 yrs, even if lobsters were absent. We argue that the lobster “invasion” triggered an alternative stable state, making a return to pre-invasion conditions unlikely

Analytic Inversion of Emission Lines of Arbitrary Optical Depth for the Structure of Supernova Ejecta

We derive a method for inverting emission line profiles formed in supernova ejecta. The derivation assumes spherical symmetry and homologous expansion (i.e., $v(r) \propto r$), is analytic, and even takes account of occultation by a pseudo-photosphere. Previous inversion methods have been developed which are restricted to optically thin lines, but the particular case of homologous expansion permits an analytic result for lines of {\it arbitrary} optical depth. In fact, we show that the quantity that is generically retrieved is the run of line intensity $I_\lambda$ with radius in the ejecta. This result is quite general, and so could be applied to resonance lines, recombination lines, etc. As a specific example, we show how to derive the run of (Sobolev) optical depth $\tau_\lambda$ with radius in the case of a pure resonance scattering emission line.Comment: 6 pages, no figures, to appear in Astrophysical Journal Letters, requires aaspp4.sty to late

Method of intervention in behavioral psychological symptoms of dementia (BPSD) in elderly patients with dementia. -Focusing on individual symptom-

Settlement influences the distribution and abundance of many marine organisms, although the relative roles of abiotic and biotic factors influencing settlement are poorly understood. Species that aggregate often owe this characteristic to larval behaviour, and we investigated whether this predisposes ascidians to becoming invasive, by increasing their capacity to maintain their populations. We explored the interactive effects of larval phototaxis and geotaxis and conspecific adult extracts on settlement rates of a representative suite of 6 species of ascidians that form aggregations in the field, including 4 aliens with global distributions, and how they relate to adult habitat characteristics. In the laboratory, the larvae were (1) held in light or dark, (2) offered the choice of settling in the light or dark, or (3) held in the presence or absence of adult extract. When confined in either light or dark conditions, all species settled equally in dark and light. Four showed strong geotaxis, 3 settling preferentially on the bottom of experimental chambers, and one on the top. Offered a choice between dark and light, 2 species settled preferentially in the dark with no geotactic preferences and another 2 showed an interaction between light and geotaxis. For 4 of the species, the responses of settlers accorded with, and may contribute to, adult orientation patterns in the field. Adult extracts inhibited settlement of 3 species and failed to influence settlement of the other 3, arguing against conspecific attraction being a cause of aggregation and an explanation of the propensity of ascidians to become invasive