No genetic differentiation of giant clam (Tridacna gigas) populations in the Great Barrier Reef,Australia

Six Tridacna gigas populations were sampled in 1990 from locations throughout the central and northern Great Barrier Reef (GBR). Despite separations in excess of 1000 km, mean Nei's unbiased genetic distances among the populations was 0.0007. The complete lack of spatial variation observed among populations did not results from lack of genetic variability. Genetic variation within populations was high, with mean heterozygosities from 0.221 to 0.250. Gene frequencies were consistent with expectations under conditions of Hardy-Weinberg equilibrium. These data suggest panmixis, or random mating, throughout the highly connected reef system of the central and northern GBR. The large gene exchange among the giant clam populations has important implications for conservation management of one of the few large populations of T. gigas in the world. Small local effects are likely to be overcome in time by inputs from other sources. However, large genetic perturbations, particularly from up-current sources, may spread rapidly through the population.Contribution No. 561 from the Australian Institute of Marine Science     

Decision making in dune management: theory and practice

Effective decision making depends upon the availability of quality information. Procedures involved in assessing dune vulnerability and protection require monitoring of sporadic processes and information must be collected from many discipline sources. In particular, a significant challenge to strategic management is recognition of subtle discontinuities which could undermine the long term stability of the dune system. These changes may be irregular and/or non linear requiring managers to be aware of existing parameters, patterns and emerging discontinuities. A range of components within the system should be measured on a systematic, temporal and spatial basis. An environmentalchecklist is a useful management technique which systematises information, so that strategic objectives can be made operational and achievable. Problems can be identified and solved with this methodology particularly if it is incorporated into aW problem solving model. The checklist procedure proposed in this paper has been developed and tested in field conditions for a range of north-west and south-European dune systems. Whereas a universalchecklist applicable to all systems is utopian in aim, intra and extra-regional comparisons can be undertaken with only minor modifications of some components. Parameters covering site and dune morphology, beach condition; surface character of the seaward 200 m of the dunes; pressure of use and recent protection measures are the basis for calculating vulnerability and protection indices. The balance between these indices can be determined, analysed and form the foundation for future informed management decisions.     

Chemically mediated burrow recognition in the Mexican tarantula <Emphasis Type="Italic">Brachypelma vagans</Emphasis> female

Chemically mediated communication is common in spiders but has been poorly studied in burrowing tarantulas. This study aimed to determine whether chemical cues influence the behaviour of females of Brachypelma vagans, a Mexican species of tarantula, during encounters with previously inhabited burrows or with extracts from the silk of conspecific females. In laboratory choice tests, female tarantulas entered a burrow that had previously been inhabited by a conspecific female significantly more frequently than a burrow that had never been inhabited. The identity of the previous inhabitant also affected the number of spiders that chose to enter a burrow. Spiders were quicker to choose and enter a burrow previously inhabited by themselves than a burrow previously inhabited by a conspecific or a burrow that had not been previously inhabited. Hexane, methanol and dichloromethane extracts of conspecific silk elicited different responses from female tarantulas when extracts were placed on filter paper disks at one end of an experimental arena with a control filter paper disk, on to which the corresponding solvent alone had been pipetted, placed on the other end of the arena. Spiders showed the strongest responses to hexane extracts of silk, with a significant preference to move towards the hexane extract and a significantly greater period of time spent in proximity to the hexane extract compared to the control disk. Overall and in contrast to expectations, tarantulas were most strongly attracted to the cues left by other conspecific females. As encounters between B. vagans females usually lead to aggression and mortality of one of the participants, we conclude that chemical cues are not signals that are deliberately released by burrow-inhabiting females but may inadvertently escape and cannot be easily suppressed.     

Near-real-time determination of hydrogen peroxide generated from cigarette smoke

The ability to monitor hydrogen peroxide (H2O2) in aqueous smoke extracts will advance our understanding of the relationship between cigarette smoke-induced oxidative stress, inflammation, and disease and help elucidate the pathways by which the various smoke constituents exert their pathogenic effects. We have demonstrated, for the first time, the measurement of H2O2 production from cigarette smoke without prior separation of the sample. Cigarettes were tested on a commercial smoking machine, such that the whole smoke or gas vapor phase was bubbled through phosphate buffered saline solution at pH 7.4. Aliquots of these solutions were analyzed using an Amplex Red/horseradish peroxidase fluorimetric assay that required only a 2 minute incubation time, facilitating the rapid, facile collection of data. Catalase was used to demonstrate the selectivity and specificity of the assay for H2O2 in the complex smoke matrix. We measured approximately 7-8 microM H2O2 from two reference cigarettes (i.e., 1R4F and 2R4F). We also observed 9x more H2O2 from whole smoke bubbled samples compared to the gas vapor phase, indicating that the major constituent(s) responsible for H2O2 formation reside in the particulate phase of cigarette smoke. Aqueous solutions of hydroquinone and catechol, both of which are particulate phase constituents of cigarette smoke, generated no H2O2 even though they are free radical precursors involved in the production of reactive oxygen species in the smoke matrix.     

Fat solubility — A property of environmental relevance?

Solubilities in fats ranging from 0.88 g l^?1 to completely miscible are reported for twelve organic chemicals. Comparison of these and other literature values with bioconcentration factors and octanol: water partition coefficients indicate that fat solubility is not a reliable predictor for either parameter. The results for the solubilities of seven chemicals in eight different fats cover a restricted range, indicating that the composition of the fat is not a critical parameter in determining the solubility.     

Function analysis as a coastal management tool: the South Wales coastline,UK

Fifteen beaches from the Swansea Bay coastal sediment cell, South Wales, UK, were analysed via function analysis, involving assessment of specific environmental and socio-economic indicators. These were allocated scores from field surveys and extensive desktop studies, which included beach awards, relevant shoreline management plans, planning and conservation designations and current legislation. Normalised scores allowed production of a conservation/development matrix, enabling beach location in conservation, development or conflict fields, which results appropriately identified. Conservation field beaches tended to have a low density residential hinterland with little or no commercialisation. Conversely, beaches that leant towards the development field had a high density residential hinterland and were highly commercialised. Evaluation showed the importance of planning legislation in conflict areas and identified locations of development potential, where significant environmental consequences would be unlikely. This representation could be used for evolution of conservation/development status within coastal areas, enabling policy adjustment as necessary. It will also enable future sustainability assessment and it is suggested that indicators could be modified to reduce environmental emphasis and provide a more uniform socio-economic consideration.     

Chaetognaths and ctenophores in the holoplankton of the Bristol Channel

The geographical distributions, seasonal variations in numerical abundance and biomass (mg C m^-3) of the predators of the holoplankton of the Bristol Channel, between November 1973 and February 1975, are described. The predator numbers and biomass were dominated by the chaetognath Sagitta elegans Verrill. This species represented 96% of the holoplankton carnivore biomass in the outer, seaward region of the Channel and 60% in the inner region; the remainder being ctenophores. The maximum numerical abundance of S. elegans occurred in September at 129 individuals m^-3 (18 mg C m^-3). Juveniles (<5 mm) reached maximum numbers of 55 individuals m^-3 during June, August and September, demonstrating the reproductive activity of the population. The peak numbers were probably the result of the development of two major generations over the 90 d period from mid-June to mid-September. The tentaculate ctenophores were represented by Pleurobrachia pileus (O. F. Müller). The highest abundance was 81 individuals m^-3 (3.0 mg C m^-3) at a single site in July in the South Central Channel. However, June was the only month when the ctenophores dominated the carnivore biomass in all regions of the Channel; thereafter, S. elegans was more abundant. Reproduction of the ctenophore occurred from April to September, with juveniles reaching maximum abundance in June at 12 individuals m^-3. The estimated food demand of the population in May for the outer region of the Channel was approximately 31% of the daily production of copepods. When the population reached its peak abundance in June, the estimated food requirement outstripped the daily production of copepods and a decline in both the prey and predator standing stocks was observed. Similar estimations were derived for the inner region of the Channel. S. elegans increased from a standing stock of 0.038 mg C m^-3 in March to 6.35 mg C m^-3 in September. Estimates of the copepod production compared with the derived demand of the chaetognath population showed that the decline in the copepods in the late summer was the result of feeding by this predator. The holoplankton carnivore population was approximately 66% of the copepod standing stock for the 10 mo period November 1973 to September 1974 in the outer region of the Channel and 45% of that in the inner region. The carnivores formed the greater part of the total holoplankton biomass from September through the winter months to February, suggesting a predator-dominated community.     

Seasonal population structure,vertical distribution and migration of the chaetognath Sagitta elegans in the Celtic Sea

The biology of the chaetognath Sagitta elegans Verrill has been much researched, but detailed studies of population structure have generally been conducted in coastal water where dynamic tidal conditions may cause difficulty in interpretation of data. The resolution of sampling examining vertical distribution and diurnal migration has also been rather coarse. During a series of eight cruises to a seasonally thermally stratified sampling site in the Celtic Sea in 1978 and 1979, detailed vertical zooplankton profiles were taken to study the seasonal population structure, vertical distribution and migration of this species. The overwintering stock of S. elegans (22 to 52 individuals m^-2, 0 to 90 m) had a wide range of lengths (5 to 20 mm) and matured in 1978 from early March, spawning several times before dying out by late July. Young produced by the overwintering stock started to mature in July and population numbers reached their highest in August (2483 m^-2, 132.8 mg C m^-2) when sea temperature peaked (17.1°C). By October, the population of S. elegans declined (284 m^-2), which was thought to be due to a combination of lower sea-water temperature, competition for and availability of food, and predation. Because of the length range of the overwintering population (5 to 20 mm), it is assumed that reproduction continued at a low level over the winter, although eggs were not found in January and February, the coldest months of the year. In summer, the smallest S. elegans (2 to 6 mm) were found in the near-surface waters and did not migrate, but as their lengths increased they occupied deeper depth ranges and a portion of the population started to migrate diurnally. Individuals which did not migrate and stayed in the warmer surface waters, or those which migrated into it, matured faster than those remaining in the colder water below the thermocline. Migration to surface waters by mature individuals seemed to be stopped by high surface temperatures (17°C) and a sharp thermocline (3 C°). As sea temperature increased during the year from the winter minimum of 7.7°C, S. elegans matured at a progressively shorter length (14 mm in March 1978 to 10 mm in August). There are probably only three generations of S. elegans a year in the Celtic Sea.     

Vertical distributions of Calanus finmarchicus and C. helgolandicus (Crustacea: Copepoda)

The vertical distributions of the spring populations of Calanus finmarchicus (Gunnerus) and C. helgolandicus Claus are described and compared. The differences we observed between the two species have probably confused the understanding of the vertical distribution and development of the populations of Calanus spp. in the shelf seas around the United Kingdom where the species occur together. The results imply that these two congeneric species have different behaviour patterns which minimise interspecific competition where the species have sympatric distributions. C. finmarchicus has its younger development stages overlying the older stages in the water column. In C. helgolandicus the converse is true; i. e., the majority of the populations of Stage I and II copepodites of the first spring generations are found below the thermocline. It is also suggested that the different behaviour patterns lead to different feeding regimes and strategies.JONSDAP Contribution No. 52     

Environmental influence on the locomotor activity rhythm of Talitrus saltator (Crustacea: Amphipoda)

The persistence and precision of the endogenous, nocturnal, circadian locomotor rhythm of the sand-beach amphipod Talitrus saltator is characterised, and the influence of substrate availability, photoperiod, temperature and relative humidity as potential environmental synchronizers of the rhythm is assessed. Individual, cyclic light-dark and temperature regimes synchronize and modify the laboratory activity pattern, but substrate availability and relative humidity have no significant long-term effect. Under simulateneous experimental regimes simulating field conditions of photoperiod, temperature and relative humidity the rhythm is entrained solely by photoperiod. The implications are discussed in relation to field behaviour.