The age and growth of hottentot seabream Pachymetopon blochii before and after the South African linefish state of emergency in 2000

The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as L_t = 418.063 (1 – e^{?0.104(t – [?4.709])}) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management.     

The sandstone fantasy of Petra

The rose-red city half as old as time is an incredible series of monuments carved out of Cambrian sandstone, which offers more than a little geological interest. Both the site of Petra and its approach canyons are tightly controlled by the geology, and the sandstone itself is mineralized and coloured on a surprising scale.     

Population ecology of Sinelobus stanfordi (Crustacea: Tanaidacea) in a temperate southern microtidal estuary

Sinelobus stanfordi is a tanaidacean of worldwide distribution of considerable significance within coastal ecosystems. The aim of this research was to provide essential information on the poorly-known population biology of this species. Benthic samples were taken seasonally from winter 2005 through summer 2007 along 155?km of shoreline within the Río de la Plata Estuary, Argentina. The density of this tanaidacean was higher in vegetated than in bare sediments. The smaller individuals flourished in spring and summer, whereas the larger mature members prevailed in the cooler seasons. Females were always twice as abundant as males. Copulatory females, with 18?±?8 eggs each, were collected during all the seasons. Five cohorts were distinguished by the von Bertalanffy growth function. This research represents a baseline investigation for future studies on the population dynamics of S. stanfordi both in this estuary and in other places where this species is found.     

Use of probiotic bacteria to improve growth and survivability of farmed New Zealand abalone (Haliotis iris)

The effects of two probiotic feeds containing two and three bacterial isolates were evaluated on the growth performance of New Zealand abalone (Haliotis iris). Probiotic bacteria were isolated from the guts of healthy adult abalone. The isolates were screened qualitatively and quantitatively according to their ability to hydrolyse nutrients (i.e. proteins, starch and alginate), produce acid and resist bile salts. Based on the screening results, we developed a multi-strain conglomerate of 2- and 3- probiotic bacterial strains that were supplemented into a commercial abalone feed to use in our experiments. The 2-probiotic conglomerate consisted of Exiguobacterium JHEb1 and Vibrio JH1, and the 3-probiotic conglomerate consisted of Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc. The probiotic feeding trial involved abalone juveniles (20–30 mm in maximum shell length). Both probiotic feeds significantly improved abalone growth compared to that of the unsupplemented feed. The 3-probiotic supplemented feed produced a significant shell length increase of 20.9%, a wet weight gain of 19.8% and a five-fold reduction in mortality compared to the controls. The 2-probiotic supplemented feed resulted in significant increases in shell length (15.4%) and reduced mortality (five-fold), but not in weight gain, compared to controls.     

Neurophysiological control of swimming behaviour,attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

Experiments were conducted to test the effect of a range of chemicals on larval responses in swimming behaviour, attachment and metamorphosis of the black-footed abalone (Haliotis iris). The effect of antibiotics on larval survival was first tested within negative (filtered seawater) and positive (GABA at 10^?5, 10^?4 and 10^?3 mol L^?1) control assays over 3 days. This experiment corroborated the effectiveness of using antibiotics to improve survival of larvae without obvious synergistic interactions with the GABA inducer or confounding effects of potential bacterial interactions. Chemical treatments (acetylcholine, potassium chloride, dopamine and glutamine) were then tested at various concentrations for their ability to modulate swimming behaviour and induce larval attachment and metamorphosis over 14 days. Generally, larval state shifted from swimming to attached, and from attached to metamorphosed, in the control and treatments over time. However, the peak percentage of attached and metamorphosed larvae varied in time among chemicals and concentrations. While overall percent metamorphosis was minimally enhanced after 14 days of exposure to some chemical treatments at certain concentrations, all treatments displayed significant capacities to down-regulate larval swimming and induce early attachment and metamorphosis. Mortality was recorded throughout the duration of the experiment, and was generally low (<20%) across controls and most treatments for exposures of less than 12 days. Interpretations of specific results from this study are used to elucidate neurophysiological control of larval activities for this abalone species. Comparisons with other marine invertebrates highlight the specificities of chemical cues and endogenous regulatory mechanisms across relatively closely related taxa.     

PLANE-WAVE CONSTRAINTS IN 2D FILTER DESIGN1

A method is presented for developing and/or evaluating 2D filters applied to seismic data. The approach used is to express linear 2D filtering operations in the space-frequency (x–ω) domain. Correction filters are then determined using plane-wave constraints. For example, requiring a vertically propagating plane wave to be unaffected by migration necessitates application of a half-derivative correction in Kirchhoff migration. The same approach allows determination of the region of time-offset space where half-derivative corrections are correct in x–t domain dip moveout. Finally, an x–ω domain dip filter is derived using the constraint that a plane wave be attenuated as its dip increases. This filter has the advantage that it is significantly faster than f–k domain dip filtering and can be used on irregularly spaced data. This latter property also allows the filter to be used for interpolation of irregular data onto a regular grid.     

四川北部米仓山地区下三叠统内部不整合面的发现及其意义

前人认为四川北部米仓山地区下三叠统内部各组地层之间是整合接触,然而通过构造和沉积学的研究发现下三叠统内部(奥伦尼阶)存在一个区域不整合面。在沉积上表现为环米仓山地区广泛发育的陆相和海相碎屑岩,与下伏地层呈不整合接触。地震剖面上表现为不整合面上下的变形特征不一致、不整合面下部地层被削截、古构造的存在等等,通过对古褶皱和古断裂的平面投影,发现古构造走向为东-西向,与勉略构造带走向一致。综合区域大地构造历史,笔者认为在早三叠世奥伦尼期(约249.7～245.0Ma)南秦岭造山带和上扬子地块就已经发生碰撞,碰撞引起了米仓山地区强烈的构造变形,形成这一区域不整合面。该碰撞时间不一定是南秦岭造山带和上扬子地块在此处的初始碰撞时间。     

Excursion guide 11: Mount St Helens

The 1980 eruption of the Mount St Helens volcano produced a huge crater, massive debris flows and truly remarkable blast effects. All the features are still very visible, and the site offers easy access for an unforgettable visit.     

Tectonic control on peritidal carbonate parasequence formation: an investigation using forward tectono-stratigraphic modelling

Studies of Quaternary extensional faults indicate that they have instantaneous amounts of throw (0·4 to 4 m), average slip rates (0·05 to 2·8 m kyr⁻¹) and frequency of recurrence (<40 000 years) accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences (PCPs). Hangingwall sites and graben are characterized by fault down-dropping together with regional subsidence, and footwall sites and horsts by fault-related uplift alternating with periods of regional subsidence. The relative sea-level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program SedTec2000 to simulate how fault-related changes in accommodation space can account for high-frequency PCP formation. Each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings. High-frequency cycles in hangingwall sites are either symmetric (deepening then shallowing upward) or asymmetric (shallowing-upward). The major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space. High-frequency cycles in footwall sites and horsts comprise shallow subtidal facies, with no distinctive bathymetric trends, capped by erosional boundaries generated by footwall uplift. The modelled cycles are of the same thickness, with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea-level changes or autocyclic processes. These numerical experiments demonstrate that high-frequency PCPs can be generated by tectonic, fault-related processes, a hypothesis that is frequently discounted.