Recovery of benthic communities at Macquarie Island (sub-Antarctic) following a small oil spill

Intertidal communities at Macquarie Island (sub-Antarctic) were re-evaluated seven years after a small oil spill resulting from the grounding of the “Nella Dan”, and six years after the first assessment of biological impact. Sampling was conducted to evaluate community structure in three zones of the exposed rocky shore (upper red, kelp, and lower red) and in samples of Durvillaea antarctica holdfasts. There were no significant differences between the community structure in oiled and control locations in any of the three shore zones, but holdfast macrofaunal communities at oiled sites still showed evidence of impact. Holdfast community-structure in samples from heavily oiled sites showed moderate levels of recovery, with increased abundances of species which were considered sensitive to the oiling in the first post-impact studies and decreased abundances of opportunistic polychaete and oligochaete worms. In contrast, samples collected from the moderately oiled location at Secluded Bay showed little evidence of recovery. Holdfasts at this site were filled with sediment containing traces of diesel oil, and the macrofaunal community was dominated by opportunistic worms. This study clearly indicates that even small incidents of anthropogenic perturbation can have long-lasting consequences for marine communities at Macquarie Island. Received: 23 July 1997 / Accepted: 5 February 1998     

Effects of Trichodesmium spp. blooms on penaeid prawn larvae

The effects of blooms of the cyanobacterium Trichodesmium spp. on penaeid prawn larvae were examined using in situ and laboratory rearing experiments and plankton surveys in Albatross Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom of Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compared with times when diatoms were dominant in the same study area. Laboratory experiments confirmed the in situ results. None of the prawn larvae fed Trichodesmium sp. in laboratory experiments developed beyond the first protozoeal stage. In contrast, 94% of prawn larvae fed the green flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutritional value, resulting in starvation. A 7 yr plankton survey, from 1985 to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium spp. and that maximum abundance of prawn larvae generally occurs just after the bloom. There was a negative correlation between the abundance of larvae and the abundance of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that variations in both timing and magnitude of Trichodesmium blooms are important determinants of prawn larvae abundance in Albatross Bay. Received: 28 April 1997 / Accepted: 2 April 1998     

Factors influencing food choice by the seaweed-eating marine snail Norrisianorrisi (Trochidae)

Through two-choice gustatory experiments, a␣preference hierarchy was established␣for␣the␣herbivorous gastropod Norrisianorrisi Sowerby, with laminarialean kelps preferred over all other seaweeds. Among the kelps, laminae of Macrocystispyrifera were slightly preferred over Egregiamenziesii, and both were strongly preferred over sporophylls of Eiseniaarborea. E.arborea, the least preferred kelp, was consistently chosen over other algae common in the snail's habitat (Halidrysdioica, Dictyotaflabellata, and Pterocladiacapillacea) and over seaweeds believed to be edible and palatable based on their morphology, structure, and secondary chemistry (Endarachnebinghamiae, Mazzaellaflaccida, and Ulvalobata). The morphologies and structural toughness of tested seaweeds varied significantly as did their nutritional (% carbon, % nitrogen, C:N ratio, and % ash) contents and phlorotannin concentrations; however, snails preferred to feed on kelps regardless of nutritional content, toughness or phlorotannin concentration; and among kelps preferred to feed on the least tough species (based on penetrometer measurements), which also were those containing the lowest phlorotannin concentrations. Preference for kelp was not upheld in experiments using agarose thalli to which freeze-dried powder, of either the kelp Eiseniaarborea or non-kelp Endarachnebinghamiae was added, suggesting the destruction of attractant chemicals during the making of the artificial foods. Our data suggest that the preference of N. norrisi for kelps over other potentially edible and palatable seaweeds may not be related to nutritional content, but instead may have evolved in response to factors such as availability, habitat provision, or refuge from predation. Received: 27 September 1996 / Accepted: 7 October 1997     

Effects of UV radiation of different wavebands on pigmentation, 15N-ammonium uptake, amino acid pools and adenylate contents of marine diatoms

Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol% CO₂, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms. The uptake of ¹⁵N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP) were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism in connection to pigments and supply with energy. Received: 13 May 1997 / Accepted: 11 October 1997     

Instrument Choice When Regulators and Firms Bargain

We compare outcomes with an emissions tax and an emissions standard when a firm and regulator engage in cooperative bargaining over the stringency of the regulation. Bargaining is motivated by giving the firm a choice of abatement technologies. If the firm's preferred technology differs from the regulator's, the first-best outcome is not an equilibrium of the traditional noncooperative game in which the regulator is a Stackelberg leader. The regulator may therefore choose to offer the firm a more lenient regulation if it agrees to switch technologies. We find that the resulting bargaining outcomes differ for a tax and a standard even though information is symmetric, and we identify conditions under which each instrument yields lower social costs.     

Nutrient transfer functions: the site of integration between feeding behaviour and nutritional physiology

Summary. We describe and extend a graphical approach to quantitative nutrition that focuses on the interplay between behavioural and physiological components of nutritional regulation. The site of integration is the nutrient transfer function, which is the function describing the time course of nutrient transfer between serially connected nutritional compartments (e.g., from the gut to the blood). The relationship between the shape of the nutrient transfer function and the temporal patterns of feeding determines the values of two key quantitative parameters of nutrition: the rate ('power') and the efficiency of nutrient acquisition. The approach can be extended to consider, in addition to the short-term behavioural and physiological decisions made by animals, some ecological determinants and longer-term, life history consequences of such decisions. Most importantly, this category of models can provide insights into the interplay among the various nutrients in an animal's diet. We illustrate this using hypothetical examples, and also present preliminary data for the power-efficiency relationships of protein and digestible carbohydrates in locusts. Finally, we consider existing evidence for the various means available to these and other insects for regulating such relationships. Received 24 September 1997; accepted 9 December 1997.     

Modelling and assessment of South African elephant Loxodonta africana population persistence

The use of a quantitative population growth model to investigate the persistence of South African elephant populations is explored. The model provides quantitative assessments of population persistence and confidence intervals for estimated parameters based purely on population size estimates. The analysis supports the view that most of the larger populations in the region are secure. This view is further supported by a lack of density dependent effects in most of the recovering populations and the high population rates of increase observed. This predominantly positive prognosis is in contrast with that emerging from most of the rest of the African continent where the populations are under greater threat because of habitat restriction and direct human conflict. This preliminary assessment of elephant population persistence suggests that “viable” populations may lie between 400 and 6000 individuals. Although not inconsistent with information-greedy genetic and demographic models, the relationship between population growth versus genetic and demographic models should be further investigated. The implementation of a metapopulation management strategy towards these smaller populations is advocated. In addition, as all of the populations included in this analysis have been afforded some degree of protection since the 1920s, continued protection would be a prerequisite for their continued survival.