Annual cycle of biomass of a threatened population of the intertidal seagrass Zostera japonica in Hong Kong

The phenology and primary productivity of a population of Zostera japonica (Aschers. & Graebn.) threatened by the construction of Hong Kong's new international airport were studied over a 12-month period. The need to conserve the population, and the small leaf size of Z. japonica rendered traditional destructive or marking techniques inapplicable for percentage cover and biomass estimation. A nondestructive method based on image analysis techniques was therefore devised for repeated estimation of percentage cover, biomass and leaf area index. This technique, which involved random quadrat sampling, photographic recording and image analysis, was able to provide data on the three parameters with acceptable precision and was cost-effective in the field. Z. japonica demonstrated a strongly seasonal cycle of vegetative growth, with different patterns for leaf density (peak in March) and overall bed area (peak in June). Total (above- and below-ground) net primary productivity was estimated at between 344 and 688 g AFDW m⁻² yr⁻¹. Percentage cover of Z. japonica was negatively correlated with total suspended solids (TSS) in the water column while total bed area was negatively correlated with water salinity. Increased sedimentation associated with the new airport project was identified as one important factor affecting the growth of the seagrass, as TSS reached the high level of ≈1 g DW l⁻¹ during the first half of the study period. Sediment traps set in the beds also recorded potential sedimentation rates at between 2.89 and 14.5 mg cm⁻² d⁻¹. This high turbidity resulted in a sharp decrease in the density of Clithon spp., the dominant grazers of epiphytic algae on Z. japonica. Effects of sedimentation and shading on growth of Z. japonica were investigated by field manipulative experiments. Experimental increase of sedimentation rate and shade both resulted in larger decreases in percentage cover and above-ground AFDW compared with the control. Received: 3 March 1997 / Accepted: 14 March 1997     

Effects of Water Management on the Wetlands of the Colorado River Delta, Mexico

The lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. No river water is officially appropriated to support delta wetlands, yet large marsh areas of conservation interest still exist below the agricultural fields in Mexico. These are supported by flood water, agricultural drainage water, municipal sewage effluent, and seawater in the intertidal zone. From 1973 to 1993 the area of freshwater and brackish marsh varied widely, from 5800 to 63,000 ha. A new opportunity exists to restore wetlands in the delta now that the upstream water impoundments on the Colorado River are filled and flood flows are once again being directed to the delta. But flood control structures now channel most of the flood water directly to the sea, and most of the effluent waters are deposited in evaporation basins rather than used to support wetlands. If the Yuma Desalting Plant in the United States becomes operational and if the Rio Hardy wetlands continue to be drained, the area of brackish wetlands could decrease to less than 2000 ha in the near future. Preserving the remaining wetlands will require a binational water management plan. The plan should maximize the benefits to wetlands of flood and irrigation return flows that enter the delta, and it should minimize flood risks.     

Toward a Complete Economic Theory of the Utilization and Management of Recreational Fisheries

A model of individual behavior for recreational fisheries which considers both the participation decision and the activity level decision is developed. The model also distinguishes between the catch rate, which is a biologically determined parameter, and the landings rate, which is a control variable. Individual and fisherywide equilibria under open access are described for both homogeneous and heterogeneous participants. Optimal utilization is also described. Optimal utilization differs from open access in terms of activity levels of participants and number and type of participants. Regulations to achieve optimal utilization are described.     

Resting egg formation and hatching of the S-type rotifer Brachionus plicatilis at varying salinities

Several live specimens of the blue-ringed octopus Octopus maculosus were collected from the Philippines in November 1985, and from Japan in February 1986, and the distribution of toxicity, along with toxin composition, in the posterior salivary gland and other soft parts were examined. Tetrodotoxin (TTX: 1400 mouse units g^-1) was detected in the posterior salivary gland of a Japanese specimen, while not only the salivary gland but other soft parts were toxic in the Philippine specimens. The Philippine specimens contained TTX and anhydrotetrodotoxin, the Japanese specimen TTX, 4-epitetrodotoxin, and an unknown toxin. The posterior salivary gland, intestine and other parts were excised from the Philippine specimens and examined for bacterial flora. Twenty-two dominant strains were isolated and cultured in a 2xORI medium (Ocean Research Institute, Simidu and Tsukamoto 1985) at 20°C for 20 to 48 h. Cells were harvested by centrifugation, and disrupted by ultrasonication. The toxins were partially purified from the cell lyzate by ultrafiltration and Bio-Gel P-2 column-chromatography. Instrumental analyses disclosed that 16 of the 22 strains produced TTX and/or related substances. Six strains which clearly exhibited TTX productivity were identified as Alteromonas (2 strains), Bacillus (2), Pseudomonas (1) and Vibrio (1), based on biochemical and biological characteristics. Of these, one strain each of Bacillus and Pseudomonas produced TTX at a level detectable by the mouse assay.     

Fate of petroleum hydrocarbons taken up from food and water by the blue crab Callinectes sapidus

Radiolabeled paraffinic and aromatic hydrocarbons, including benzopyrene, fluorene, naphthalene, methylnaphthalene, methylcholanthrene, hexadecane, heptadecane and dotriacontane, were taken up from food and water by the blue crab Callinectes sapidus. In 2 days, approximately 10% of the benzopyrene and fluorene were taken up from the water when their concentrations were 2.5 and 30 g/l, respectively. When given food with radiolabeled hydrocarbons, 2 to 10% of the hydrocarbons were assimilated by the carbs, with the remainder excreted. After uptake of hydrocarbon from water or food, a major pathway for the elimination of hydrocarbon and metabolites was through fecal material. All hydrocarbons used in the study were metabolized, with similar rates for both paraffinic and aromatic hydrocarbons. More than 50% of the radioactivity assimilated by the crabs was in the hepatopancreas, suggesting that the hepatopancreas was the site of hydrocarbon metabolism. Twenty-five days aftex exposure to radiolabeled hydrocarbons, radioactivity was found only in the hepatopancreas. The hepatopancreas contained highly polar hydrocarbon metabolites, including dihydroxy-compounds and their conjugates, while blood contained both monohydroxy-and dihydroxy-compounds. No evidence was found of storage of hydrocarbons by any of the crab tissues.     

Enrichment of potentially toxic elements in areas underlain by black shales and slates in Korea

The Okchon black shale in Korea provides an important example of natural geological materials containing toxic elements; the Chung-Joo, Duk-Pyung, Geum-Kwan, I-Won and Chu-Bu areas are underlain by these black shales and slates of the Guryongsan Formation. This formation is part of the Okchon Group which is found in the central part of Korea. Geochemical surveys were undertaken in these five study areas in the Okchon Zone in order to examine the level of enrichment and dispersion patterns of potentially toxic elements in rocks and soils. After appropriate preparation, samples were analysed by instrumental neutron activation analysis and inductively coupled plasma atomic emission spectrometry for a range of elements. Arsenic, Cu, Mo, V, U and Zn are highly enriched in the Okchon black shales and their mean concentrations are significantly higher than those in black slates. These elements are closely associated with one another from a geochemical viewpoint and may be enriched simultaneously. Mean concentrations of As, Mo and U in soils derived from black shales occurring in the Duk-Pyung and Chu-Bu areas are higher than the permissible level suggested by Kloke (1979), and the enrichment index decreases in the order of Duk- Pyung > Chu-Bu > Chung-Joo > Geum-Kwan = I-Won areas. Uranium-bearing minerals such as uraninite and brannerite have been identified in black shales from the Chung-Joo area by electron probe micro-analysis. Uraninite grains are closely associated with monazite and pyrite with a grain size ranging from 2m to 10m whereas brannerite grains occur as a euhedral form 50m in diameter.     

Heavy Metals in the Bed and Suspended Sediments of Anyang River, Korea: Implications for Water Quality

The objective of this study is to compare Anyang River bed sediments with water chemical composition and to assess the anthropogenic chemical inputs into the river system. Eight sampling locations were chosen along the river channel. Bed and suspended river sediments and water samples were collected, and analyzed for their chemical and physical composition. Data revealed that trace element concentrations in the river water were generally below world average, except for As, Mn, Ni and Cr. Among the three phases: water, bed and suspended sediment, more than 99% of the trace elements was associated with the bed sediment. Concentrations of trace elements in the sediment were a function a particle size distribution and organic content. The calculated degrees of enrichment based on the least influenced sample (ASD 1) indicated the river sediments were enriched with respect to background. The enrichment factors for Pb, Zn and As were relatively lower than for Cr, Co, Ni and Zn. The difference in the enrichment seems to reflect the human activities influence in the basin, and specially for Cd. Speciation of the elements in the five different chemical forms in the sediment by sequential extraction indicated that the reducible fraction was predominant for Fe, Zinc and Cu showed an irregular variation among the different fractions; whereas, Cd and Pb were more regular. Zinc and Cu highly existed mostly in exchangeable forms. Acid soluble and reducible forms were also important for most metals. The speciation implies that the metals associated with the sediment are subject to release into water bodies as goechemical variables (pH and Eh) change. Currently, the introduced metals are deposited near the source area and are mostly associated with the sediment, implying that the river bed sediment acts mainly as a sink, rather than a pool. The accumulated and enriched toxic trace elements can pose a potential pollution of river water.     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.