Spatial and interannual variation in the faunal distribution at Broken Spur vent field (29°N, Mid-Atlantic Ridge)

Initial ecological observations at Broken Spur in 1993 suggested a low biomass relative to other deep-water vent communities known along the Mid-Atlantic Ridge. The persistence of a low shrimp biomass over 15 mo at Broken Spur vents appears to refute the hypothesis that the community is expanding through reproduction and immigration to occupy habitat vacated during a recent period of hydrothermal quiescence or catastrophe. Although the absence of “swarms” of shrimp similar to those found at the hydrothermal mounds of TAG (26°N) and Snake Pit (23°N) is a visually striking feature of the majority of venting structures known at Broken Spur, the biomass of fauna other than shrimp may not be significantly less than that of other Mid-Atlantic sites. The discovery of “swarms” of shrimp at Bogdanov Site, visited for the first time in 1994, suggests that availability of substratum exposed to the flow of hydrothermal fluids, which is a function of the topography of venting structures, may be a prerequisite for the development of these dense aggregations. Two testable predictions arise from this hypothesis. Firstly, dense aggregations of Rimicaris exoculata should occur at any other structures with a morphology similar to Bogdanov Site that may be discovered in the Broken Spur vent field, and should not occur at other isolated chimney structures that may be found. Secondly, “swarms” of shrimp should appear at any Broken Spur chimneys that develop into structures with a morphology more similar to that of Bogdanov Site in future. Received: 2 July 1997 / Accepted: 9 July 1997     

Integrated ecological models: simulation of socio-cultural constraints on ecological dynamics

We suggest that general systems theory provides a common philosophical basis for dialog between ecological and social scientists interested in studying the reciprocal interactions of humans and their environment. We (1) provide a synopsis of the ‘systems approach' as viewed from the biological and social sciences, respectively; (2) develop a conceptual framework for the explicit linking of ecological and social variables, and (3) draw upon game theoretic results of the Prisoner's Dilemma to represent human decision-making quantitatively in a model that simulates the tragedy of the commons. The model consists of 5 submodels that represent the ‘observers world' and each of 4 ‘participant's worlds.' The observer's-world represents the decision processes, either Optimize or Tit-for-Tat, by which each of 2 users decides to add or remove animals. The 4 perceived worlds represent hypothetical situations in which (1) persons A and B both add an animal; (2) A adds and B does not; (3) B adds and A does not, and (4) neither A nor B add an animal. Simulation results indicate that net worth of the community and of each person individually under Tit-for-Tat is more than double the net worth attained under Optimize. Replacement of the static payoff matrix assumed in game theory with a dynamic quantitative model illustrates how ‘norm-based' approaches to ecosystem management can outperform optimizing approaches based on predicted outcomes. Although ‘soft systems' techniques may better help decision-makers reach norm-based agreements on ecosystem management, quantitative models have more explanatory value, and if developed sufficiently such models could incorporate complex social dimensions that would enhance further their explanatory value.     

Sabaki River sediment load and coral stress: correlation between sediments and condition of the Malindi-Watamu reefs in Kenya (Indian Ocean)

Sediment discharges from rivers have a negative impact on coral reef ecosystems. Indicators of coral decline measured in the present study were: (1) injury to living stony corals; (2) soft coral cover; and (3) bare rocky substrate suitable for colonization by corals. The relationship between these indicators and the distribution of terrigenous sediment was studied for the Malindi-Watamu fringing reef complex along the Kenyan coast off East Africa during 1982 and 1983. Decline of this reef had been repeatedly noted during the preceding decade. The influence of terrigenous sediment from the Sabaki River appears to be strongest in the Watamu area in the south and in the northern-most part of the Malindi reef area. Correlations, between each of the above three coral stress response indicators, on the one hand, and quantitative indicators of sediment loading, on the other hand, were not clear. However, a combined coral stress indicator involving all three factors was shown to have a clear relationship with terrigenous sediment loading and provided a rapid means of field evaluation of the effects of sediment stress on stony corals. Values for the combined coral stress indicator were found to increase in proportion to increasing values of terrigenous sediment loads in both study areas. A higher coral stress indicator value means a high proportion of injured or algae infested corals, and/or a high soft coral cover, and/or a high proportion of rocky substrate suitable for, but unoccupied by, living corals.     

Chitinolytic enzymes in the integument and midgut-gland of the shrimpPalaemon serratus during the moulting cycle

Chitinase andN-acetyl--D-glucosaminidase activity were quantified inPalaemon serratus (Pennant) integument and midgut gland during the moulting cycle. Studies were performed on specimens collected near Concarneau, France, in July 1989. The changes in specific activity are different in the two organs: in the midgut gland enzymatic activity is high throughout the whole moulting cycle with a weak peak at the early premoult Stage D1, whereas in the integument the activity of both enzymes is very low throughout post- and intermoult stages and rises only after premoult Stage D1. The highest specific activity is reached in D1 for chitinase and somewhat earlier (D1) forN-acetyl--D-glucosaminidase. The increase in specific chitinolytic activity coincides with an increase in ecdysteroids.     

Naturally occurring radionuclides in drinking water: An exercise in risk benefit analysis

The scientific background information describing the occurrence, measurement, health effects, treatment technology, risk assessment and economic consequences of the presence of naturally occurring radionuclides in drinking water are described for 60,000 public drinking water supplies. The relevant data for the occurrence of radium, uranium and radon in drinking water supplies are discussed and analysed. Radon is of importance because it is released in the process of taking showers and baths and in washing dishes and clothes. Its progeny is then inhaled, leading to the risk of lung cancer. Radium and uranium can both cause bone cancer. The range of average occurrence of natural radioactivity in drinking water is as follows:²²⁶Ra, 0.3 to 0.8 pCi L^–1;²²⁸Ra, 0.4 to 1.0 pCi L^–1; uranium, 0.3 to 2.0 pCi L^–1 and²²²Rn, 500 to 600 pCi L^–1. The estimated lifetime risks due to the mean groundwater concentrations of naturally occurring radionuclides are:²²⁶Ra and^228Ra, 1.0 10^–5; uranium, 2.0 × 10^–6 and radon, 4.0 × 10^–4. The cost to reduce total radium levels to 5.0 pCi L^–1 is about $9 million. An equivalent expenditure would be required to reduce radon levels to about 4,000 pCi L^–1, or uranium levels to about 100 pCi L^–1. The problem of maximizing the total mortality and the reduction per unit dollar outlay per unit dollar cost for the uranium/radon case is examined.The thoughts and ideas expressed in this paper are those of the authors and are not necessarily those of the US Environmental Protection Agency.This paper is published as a contribution to discussion on this problem and not as a paper providing new research data.     

Cell-cell recognition system in gorgonians: description of the basic mechanism

A comparative investigation of the chemical composition of Thalassiosira antarctica var. antarctica vegetative and resting stages revealed C:N and C:chl a ratios to be lower in vegetative cells. These trends primarily reflect vegetative levels of C/cell below, and N/cell and chl a/cell levels above those of spores. There was a change in chemical composition with the initial formation of resting spores, and spores continued to modify their composition while maintained in a cyclic light/dark regime for about one and one half weeks. Most notable was a net increase in carbon and chlorophyll a per cell. Spores then subjected to darkness for over one week appeared to retain most of the carbon and chlorophyll a previously synthesized. These findings support the idea that resting spores enhance the survival capabilities of a species under adverse conditions.     

Reproductive ecology of <Emphasis Type="Italic">Fungiacyathus marenzelleri</Emphasis> from 4100 m depth in the northeast Pacific Ocean

Fungiacyathus marenzelleri (Vaughan, 1906) is a deep-water solitary coral, cosmopolitan in distribution that is found at depths of 300–6,328 m. This study examined gametogenesis, inter-annual variability and reproductive periodicity of F. marenzelleri collected from Station M (34°50′N, 123°00′W) in the northeast Pacific at a depth of 4,100 m. Samples were collected (May, June, October 1996; August 1998; February, June 2001; and June 2002) and histologically processed with spermatogenic stage, oocyte size and fecundity measured. Four stages of spermatogenesis were identified and all males contained multiple stages of sperm development in each seasonal sample. Three stages of oocyte development were identified; previtellogenic (<28–150 μm), vitellogenic (150–300 μm) and late vitellogenic (300–400 μm). Comparison of mean oocyte diameters among sampling dates showed there were no inter-annual variations or seasonal differences. Overall, fecundity was 1,290 (±407) oocytes polyp⁻¹, and with no significant differences between sample months. Fecundity was not polyp-size dependent. This study shows a similar quasi-continuous mode of reproduction to this species examined from the Northeast Atlantic Ocean, but the fecundity is reduced by 50%. The reproductive output may fluctuate in relation to the input of organic material at this site, as shown by non-significant trends in the oocyte size-frequency and fecundity data. A quasi-continuous output of gametes would promote successful fertilisation and wide dispersal of the lecithotrophic larvae.     

Using multi-objective classification to model communities of soil microarthropods

In agricultural soil, a suite of anthropogenic events shape the ecosystem processes and populations. However, the impact from anthropogenic sources on the soil environment is almost exclusively assessed for chemicals, although other factors like crop and tillage practices have an important impact as well. Thus, the farming system as a whole should be evaluated and ranked according to its environmental benefits and impacts. Our starting point is a data set describing agricultural events and soil biological parameters. Using machine learning methods for inducing regression and model trees, we produce empirical models able to predict the soil quality from agricultural measures in terms of quantities describing the soil microarthropod community. We are also interested in discovering additional higher level knowledge. In particular, we have identified the most important factors influencing the population densities of springtails and mites and their biodiversity. We also identify to which agricultural actions different microarthropods react distinctly. To obtain this higher level knowledge, we employ multi-objective regression trees.