The Ectoparasitic Gastropod Boonea (= Odostomia) impressa: Population Ecology and the Influence of Parasitism on Oyster Growth Rates

Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations.     

Classification of artificial (man-made) ground

The legacy inherited from anthropogenic processes needs to be addressed in order to provide reliable and up-to-date ground information relevant to development and regeneration in the urban environment. The legacy includes voids as well as anthropogenic deposits (artificial ground). Their characteristics derive from former quarrying and mining activities industrial processes creating derelict ground, variably consolidated made ground, and contaminated groundwater and soils. All need to be systematically assessed to inform the planning process and provide the basis for engineering solutions. Site-specific investigation needs to be conducted on the back of good quality geoscientific data. This comes from ‘field’ survey, remotely sensed data interpretation, historical maps, soil geochemical sampling, and geotechnical investigation. Three-dimensional and, in the future, four dimensional, characterization of superficial deposits is required to reach an understanding of the potential spatial lithological variability of artificial ground and the geometry of important surfaces, i.e. the boundary conditions. The classification scheme for artificial ground outlined in this paper and adopted by the British Geological Survey, will help in achieving this understanding.     

Environmental and legal aspects of karst areas

 Environmental impacts on karst settings are common as they are more sensitive than those of other rock terrains. Regulatory procedures that are effective in other rock terrains are not necessarily applicable to karst settings. Development and exploitation by man that affect the karst hydrology regime can trigger catastrophic events and result in numerous legal actions where the effects of changes go beyond property boundaries. A great variety of regulations and examples of litigation exist for karst areas. Received: 25 October 1994 · Accepted: 17 October 1995     

Tectonically dewatered slates in the Ludlovian of the Lake District,England

Multiple siltstone dykes intruded parallel to cleavage in the Ludlovian argillites and graywackes of the Lake District throw new light on the origin of slaty cleavage. Pore pressures equalling lithostatic pressure developed during the Caledonian orogeny and caused tectonic dewatering of the partially lithified sediments. Slaty cleavage was initiated as an essentially planar structure by the intrusion of thin pelitic folia during the escape of the pore water. Cleavage folia and fold axial planes may have a common geometric relationship to the deforming stresses, but are independent of each other in origin. Continued deformation after tectonic dewatering refracted the cleavage by rotation of competent layers. Critical examination of evidence supporting traditional theories of slaty-cleavage formation shows that all observed relationships are compatible with the tectonic-dewatering theory.     

Metasomatism and sulfide mobility in lithospheric mantle beneath eastern Australia: Implications for mantle Re–Os chronology

Spinel lherzolite xenoliths from Tertiary basaltic host magmas at Allyn River, eastern Australia reveal two distinct petrographic and geochemical types. One group is distinguished by xenoliths with undeformed, equilibrated microstructures and interstitial melt patches; The second group shows deformation and contains abundant fluid inclusions but no melt patches. Trace-element signatures of clinopyroxene in these xenoliths provide evidence for metasomatism by a silicate agent with hydrous component and by a carbonate-rich agent respectively.

Melt patches in the undeformed xenoliths contain secondary minerals including clinopyroxene, olivine, feldspar, Mg- and Ca-rich carbonate, apatite, ilmenite and spinel. They are interpreted to represent volatile-rich melt captured shortly prior to entrainment in the host basalt. Sulfide globules, now recrystallised to discrete sulfide phases but inferred to be molten at lithospheric mantle T and P, are closely associated with the melt patches. The close association between sulfide and highly mobile, volatile-bearing fluid has important implications for the mobility of Re and Os, the use of their isotopes in dating mantle events, and the possible effect of volatile-bearing metasomatic agents on their composition.     

New mineral activity–composition relations for thermodynamic calculations in metapelitic systems

New activity–composition (a–x) relations for minerals commonly occurring in metapelites are presented for use with the internally consistent thermodynamic dataset of Holland & Powell ( 2011 , Journal of Metamorphic Geology, 29 , 333–383). The a–x relations include a broader consideration of Fe₂O₃ in minerals, changes to the formalism of several phases and order–disorder in all ferromagnesian minerals where Fe–Mg mixing occurs on multiple sites. The a–x relations for chlorite, biotite, garnet, chloritoid, staurolite, cordierite, orthopyroxene, muscovite, paragonite and margarite have been substantially reparameterized using the approach outlined in the companion paper in this issue. For the first time, the entire set of a–x relations for the common ferromagnesian minerals in metapelitic rocks is parameterized simultaneously, with attention paid to ensuring that they can be used together to calculate phase diagrams of geologically appropriate topology. The a–x relations developed are for use in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O₂ (NCKFMASHTO) system for both subsolidus and suprasolidus conditions. Petrogenetic grids in KFMASH and KFMASHTO are similar in topology to those produced with earlier end‐member datasets and a–x relations, but with some notable differences. In particular, in subsolidus equilibria, the FeO/(FeO + MgO) of garnet is now greater than in coexisting staurolite, bringing a number of key staurolite‐bearing equilibria into better agreement with inferences from field and petrographic observations. Furthermore, the addition of Fe³⁺ and Ti to a number of silicate phases allows more plausible equilibria to be calculated in relevant systems. Pseudosections calculated with the new a–x relations are also topologically similar to equivalent diagrams using earlier a–x relations, although with many low variance fields shifting in P–T space to somewhat lower pressure conditions.     

Interpreting zirconium‐in‐rutile thermometric results

At first sight, experimental results and observations on rocks suggest that the Zr content in rutile, where equilibrated with quartz and zircon, should be a useful thermometer for metamorphic rocks. However, diffusion data for Zr in rutile imply that thermometry should not, for plausible rates of cooling, give the high temperatures commonly observed in high‐grade metamorphic rocks. It is suggested here that such observations can be accounted for by high‐T diffusive closure of Si in rutile, causing the interior of rutile grains to become insensitive to the thermometer equilibrium well above the temperature of Zr diffusive closure. Paired with comparatively slow grain boundary diffusion and problematic zircon nucleation, this allows for cases of Zr retention in rutile through temperatures where Zr is still diffusively mobile within rutile grains. Other observations that may be accounted for in this context are large inter‐grain ranges of rutile Zr contents uncorrelated with rutile grain size, and flat Zr profiles across individual rutile grains, counter to what would be expected from diffusive closure. A consequence is that it is unlikely that Zr‐in‐rutile thermometry will be useful for estimating rock cooling rates.