Self-fertilisation in Celleporella hyalina

The accumulation of parasites in a fish host is modelled as a function of the total amount of prey consumed. The accumulated parasite load is then expressed as a function of fish length so that the asymptotic growth, L , of any population of commonly infected fish can be estimated. Estimates of L are obtained for orange roughy (Hoplostethus atlanticus), albacore tuna (Thunnus alalunga) and the New Zealand southern arrow squid (Nototodarus sloanii).     

Prey selection by larval weakfish (Cynoscion regalis): the effects of prey size,speed, and abundance

We examined feeding by larval weakfish, Cynoscion regalis (Bloch and Schneider), in laboratory experiments conducted during the 1991 spawning season. under natural conditions weakfish larval development is ca. 3 wk, and we ran separate experiments with larvae of five different ages (5, 8, 11, 14, and 17 d post-hatching). We used two different size classes of rotifers (Brachionus plicatilis) and brine shrimp nauplii (Artemia sp.) as prey organisms. Contrary to results of previous research, weakfish larvae did not select prey based on size alone. When prey abundance was above 100 itemsl^-1 weakfish, larvae always chose large rotifers (length = 216 m) over small rotifers (length = 160 m). At 11 d post-hatching, larvae switched their diet from large rotifers to small brine shrimp nauplii (length = 449 m); however, when fed small rotifers and small brine shrimp nauplii the change in diet occurred at 14 d post-hatching. This pattern of selectivity was maintained in each larval age class. Early-stage larvae (5 and 8 d post-hatching) did not feed selectively when prey abundance was less than 100 itemsl^-1. Late-stage larvae (17 d post-hatching) fed selectively at abundances ranging from 10 to 10000 items^-1. Lwimming speeds of prey items, which ranged from 1 to 6 mms^-1, had no consistent effect on prey selection. These results suggest that weakfish larvae are able to feed selectively, that selectivity changes as larvae age, and that selectivity is also influenced by prey abundance.     

Age determination and growth of the bonnethead shark Sphyrna tiburo: a comparison of two populations

From July 1982 to December 1986, a study of the age and growth of the bonnethead shark Sphyrna tiburo was conducted in Tampa and Florida Bays, Florida, USA. Tetracycline-injected sharks held in captivity and, to a lesser extent, tagged, released and recaptured, were utilized for validating the annual nature of the rings (herein defined as the narrow, translucent regions) appearing on vertebral centra. The technique was validated for all age groups (0 to 6+yr) included in the study. Marginal increment analysis likewise suggested annual ring formation. The rings formed during the winter, when water temperatures were lowest. Using the vertebral ring aging-technique, von Bertalanffy growth curves for males and females from both tampa and Florida Bays were constructed. Growth of sharks born and held in captivity demonstrated that the male and female growth curves diverge after 1 yr and that mean sizes at age are statistically distinct after 2 yr. In both populations, females grew to larger sizes tha males and apparently are longer-lived. Reproductively mature females from Tampa Bay were significantly larger than those from Florida Bay.     

In situ observations of foraging,feeding, and escape behavior in three orders of oceanic ctenophores: Lobata,Cestida, and Beroida

The foraging, feeding, and escape behaviors of members of four genera of oceanic ctenophores were studied by direct observation in the field during the summer of 1987 (7 July to 7 September) on R. V. Oceanus Cruise 191 to the Northern Sargasso and Slope water, in an area bounded by 34° to 39°N and 67° and 74°W. Patterns of water movement around these ctenophores were studied using fluorescein dye. Bolinopsis infundibulum forages vertically, capturing prey with mucus-covered oral lobes. Species of Ocyropsis forage horizontally and produce a reduced wake, due to the extreme compression of the body and the aboral location of the ctene rows. Prey are trapped by the muscular oral lobes and ingested by the prehensile mouth. In both genera, the auricles are held rigidly, and apparently are used both to reduce the pressure wave as they forage and to startle prey onto the surfaces of the oral lobes. Cestum veneris also forages horizontally, but continually reverses direction. Prey startled by the turbulent wake produced in the previous pass are captured by tentilla that stream over the sides of the body. All three species of Beroe studied swim in a spiral while foraging and produce similar wakes. Prey are ingested by the negative pressure produced by the rapid expansion of the mouth, and with the macrocilia that line the oral portion of the stomodaeum. The escape behavior of species of Bolinopsis, Ocyropsis, and Cestum appears to function primarily to elude nonvisual predators such as Beroe spp. Species of Beroe bend and swim rapidly during the escape response, and will turn themselves inside-out when repeatedly stimulated. The types of prey captured depend in part on an interplay of foraging and feeding mechanisms.     

Sulphur status in some Swedish podzols as influenced by acidic deposition and extractable organic carbon

To evaluate the changes in sulphur pools in response to acidic deposition, two studies were made-one in southwest Sweden where podzolic B horizons originally sampled in 1951 were resampled in 1989. At the Norrliden site, northern Sweden, sulphur pools in control plots were compared to plots that had been subjected to H(2)SO(4) application between 1971 and 1976. The results show that in southwest Sweden neither organic S nor extractable SO(4)(2-) increased significantly over the 38-year period, despite a decreasing pH and a high S deposition. At Norrliden, about 37% of the applied S was still remaining in the upper and central parts of the Bs horizon, most of which was inorganic sulphate. These contrasting results are explained by intrinsic differences in the soil organic carbon status between the sites-in southwest Sweden, organic carbon concentrations were high which inhibited SO(4)(2-) adsorption. Low organic carbon concentrations and high extractable Fe/Al concentrations promoted SO(4)(2-) adsorption and caused a low subsequent SO(4)(2-) desorption rate at the Norrliden site. The results suggest that sulphate adsorption may be an important mechanism which delays the response in soil chemistry to H(2)SO(4) deposition, provided that soil organic carbon concentrations are low. Organic S retention was not shown to be an important S retention mechanism in any of the sites studied.     

Dry deposition of nitrogen and sulfur to Ponderosa and Jeffrey pine in the San Bernardino national forest in Southern California

Little is known about the concentrations, deposition rates, and effects of nitrogenous and sulfurous compounds in photochemical smog in the San Bernardino National Forest (SBNF) in southern California. Dry deposition of NO(3)(-) and NH(4)(+) to foliage of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was correlated (R = 0.83-0.88) with historical average hourly O(3) concentations at 10 sites across an O(3) gradient in the SBNF. Mean deposition fluxes of NO(3)(-) to ponderosa and Jeffrey pine branches were 0.82 nmol M(-2)s(-1) at Camp Paivika (CP), a high-pollution site, and 0.19 nmol m(-2) s(-1) at Camp Osceola (CAO), a low-pollution site. Deposition fluxes of NH(4)(+) were 0.32 nmol m(-2) s(-1) at CP and 0.17 nmol m(-2) s(-1) at CAO, while mean values for SO(4)(2-) were 0.03 at CP and 0.02 nmol m(-2) s(-1) at CAO. Deposition fluxes to paper and nylon filters were higher in most cases than fluxes to pine branches at the same site. The results of this study suggest that an atmospheric concentration and deposition gradient of N and S compounds occurs along with the west-east O(3) gradient in the SBNF. Annual stand-level dry deposition rates for S and N at CP and CAO were estimated. Further studies are needed to determine if high N deposition loads in the SBNF significantly affect plant/soil nutrient relations, tree health, and the response of ponderosa pine to ozone.     

Scavenging of atmospheric formaldehyde by wet precipitation

Despite the great importance that formaldehyde has in atmospheric photochemistry, few studies have been reported on rain water. In this paper, concentrations of HCHO in rain fractions within rain events are presented. Two sampling sites were chosen: one at Mexico City, a great polluted urban area, and the second at Rancho Viejo, a forested area under the meteorological influence of the city. The results show a general decrease during the early portion of the rain event. This seems to indicate that below-cloud scavenging is the most important mechanism while, from the small variations observed in the latter portion of the rainfall, it is possible to assume within-cloud scavenging as the predominant mechanism. Using the HCHO concentrations in rain water, the mixing ratios were estimated for the two sampling sites. The values were 0.68 ppb and 0.44 ppb at Mexico City and Rancho Viejo, respectively. Measurements at ground level in Mexico City gave a mean HCHO concentration in air of 24 ppb, much higher than the estimated mixing ratio. The high levels of HCHO found in ambient air and in rain water reflect anthropogenic emissions as the potential atmospheric sources.     

Proximate and elemental composition and energy content of mesopelagic crustaceans from the Eastern Gulf of Mexico

The proximate and elemental chemical compositions of 25 species of pelagic decapod and mysid crustaceans collected from the eastern Gulf of Mexico (27°N; 86°W, 1984 to 1989) was examined. Water level ranged from 63 to 95% and increased slightly with species' increased depth of occurrence. Protein levels were generally high (1.5 to 18.3% wet wt, WW; 27.6 to 62.4% ash-free dry wt, AFDW) and comprised the primary organic component in the majority of species. Protein, both as % WW and % AFDW, decreased with increased depth of occurrence. In contrast to protein, lipid levels were low (0.5 to 8.9% WW; 5.7 to 60.9% AFDW), and increased with increased depth of occurrence. Carbon and nitrogen best mirrored measured lipid and protein levels when considered as non-protein carbon and non-chitin nitrogen, respectively. C:N ratios increased with increased depth, consistent with changes in protein and lipid with depth. Because of their compositional attributes, resident Gulf of Mexico species have a low total wet weight energy content relative to species from more productive regions. Energy content showed no significant trend with depth. Vertical migration patterns were distinctly different between shallow-and deep-living gulf species and these differences were largely responsible for the relationships observed between composition and depth. In migrating species, the protein and nitrogen content were higher, the lipid and carbon contents and C:N ratio lower, than in non-migrating species. Three deep-living species of the genus Acanthephyra were found to be compositionally atypical, resembling shallow, migrating types rather than other deep-living, non-migratory species.     

POLITICAL ECONOMICS OF OFFSHORE OIL

The exploration of offshore areas for hydrocarbons has involved new technical and economic considerations and has posed new problems, not the least of which has been the changing relationship between companies and governments. In this article, the authors present an analysis of the different perspectives and policies which emanate from national governments on the one hand and from transnational oil companies on the other. The issues examined include the considerations involved in establishing exploration legislation, post-discovery problems, the impact on revenues of increased production, the interests of companies in developing fields and the overall economic environment within which decisions have to be agreed.