The influence of flow and season upon leaf-litter breakdown in monsoonal Hong Kong streams

We investigated the effects of water extraction and flow regime on leaf litter breakdown in 10 Hong Kong streams experiencing varying degrees of extraction: five with severe extraction ([85% downstream flow removed), four with moderate extraction (20-85% removed), and one without extraction (*0% removed). Breakdown rates, macroinvertebrate assemblages and nutrients were compared in upstream (reference) reaches and downstream reaches with reduced flow in each stream during highflow (wet season) and low-flow (dry season) conditions to determine whether responses to flow were influenced by Hong Kong's monsoonal climate. Litter breakdown was slower in downstream reaches during the wet season, and discharge was the main determinant of breakdown rate in both reaches across the 10 study streams. In contrast, inter-reach differences in breakdown during the dry season were small and unrelated to flow. Instead, breakdown rates among streams were influenced by the abundance of detritivorous shredders and chironomids (Chironominae), as well as phosphate concentrations, indicating the importance of biological processing of litter under low-flow conditions. Although litter breakdown rates appear to offer a promising functional indicator of flow-reduction impacts during the wet season, the pattern seen reflected the physical effects of flow rather than any underlying biological processes, and the lack of response to flow reduction during the dry season was notable. © The Author(s) 2010.published_or_final_versionSpringer Open Choice, 21 Feb 201

Biodiversity and ecosystem functioning in a species-poor guild: A test using tropical stream detritivores

The relationship between biodiversity and ecosystem functioning (B-EF) was investigated by examining top-down effects of aquatic detritivore diversity on the functional process of leaf-litter breakdown. This study was undertaken in tropical Hong Kong where the stream detritivore guild is depauperate and loss of one or a few species might have strong effects on processes. Effects of detritivore richness and composition were investigated by comparing feeding rates of three species of detritivores with their two- and three-species mixtures in laboratory trials. The detritivores were a caddisfly larva (Anisocentropus maculatus: Calamoceratidae), a snail (Brotia hainanensis: Pachychilidae) and a shrimp (Caridina cantonensis: Atyidae). Liquidambar formosana (Hamamelidaceae) litter was provided as food. All three detritivore species had positive non-additive effects on litter processing. Per capita and mass-specific feeding rates of each species were faster in mixtures than when they were alone, although the non-additive effects of shrimps and snails were larger than those attributable to caddisflies, and thus, litter processing was strongly influenced by the composition of detritivore mixtures. The compositional effect appears to be evidence of facilitation indicating a lack of functional redundancy amongst these detritivores, probably due to their evolutionary distinctness, implying that extinction consequences in this species-poor guild will depend on the identity of the species lost. © 2010 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201

Spatio-temporal variability in the distribution of ground-dwelling riparian spiders and their potential role in water-to-land energy transfer along Hong Kong forest streams

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Muddying the Waters? The Water Pollution Control Ordinance and Defining Pollution of Rivers and Streams in Hong Kong

In this article the authors consider whether the dictionary definition of pollution adopted by the Court of First Instance in The Secretary for Justice v Flame Construction Company Limited and Others is appropriate and, in particular, whether the definition can sustain prosecutions for common types of discharges which are damaging to rivers and streams. Emphasis is placed on the difficulty of demonstrating unequivocally that ecological 'harm' is caused by discharges, as this has important implications for laws that are intended to protect the environment. The authors conclude that without an amendment to the Water Pollution Control Ordinance that would provide an appropriate definition of pollution, effective prosecutions for the pollution of rivers and streams in Hong Kong cannot be pursued.published_or_final_versio

Study of inexact modeling techniques Final report

Scale modeling antenna systems for aircraft and missiles with anechoic chamber evaluation and us

Effects of increased salinity and an introduced predator on lowland amphibians in southern China: species identity matters

abstract no. V-01-9Approximately 30% of amphibian species are threatened due to a variety of factors affecting their habitats and physiology, yet contributions that interactions among factors make to population declines are not well-explored. Two factors, introduced mosquitofish (Gambusia affinis) and increased salinity, may coincide in lowland habitats used by breeding amphibians. Mosquitofish have been introduced worldwide and can be significant predators of amphibian larvae. Salinization of wetlands is an increasing problem globally due to (1) application of road deicing salts in temperate regions, (2) irrigation practices associated with intensive agriculture, particularly in Australia, and (3) saltwater intrusion due to sea-level rise. We investigated the effects of mosquitofish (Gambusia affinis) and increasing salinity on five species of lowland wetland-breeding amphibians from southern China. We exposed anuran hatchlings to four salinity levels and two fish treatments and all combinations of the two factors in a series of experiments. Four of the species were susceptible to predation by mosquitofish, two were sensitive to increased salinity at concentrations >6% seawater, and one was tolerant of both increased salinity and mosquitofish. We found no interaction between the predator and increased salinity. Salinization and mosquitofish represent significant threats to lowland amphibians in this region and, coupled with the ongoing loss and degradation of lowland wetlands, portend a bleak future for lowland amphibian populations in the region.postprintThe 49th Annual Meeting of the Association for Tropical Biology and Conservation (ATBC 2010), Bali, Indonesia, 19-23 July 2010. In Abstract Book of the 49th ATBC Annual Meeting, 2010, p.

Secondary production and diet of an invasive snail in freshwater wetlands: Implications for resource utilization and competition

Invasive species can monopolize resources and thus dominate ecosystem production. In this study we estimated secondary production and diet of four populations of Pomacea canaliculata, a freshwater invasive snail, in wetlands (abandoned paddy, oxbow pond, drainage channel, and river meander) in monsoonal Hong Kong (lat. 22°N). Apple snail secondary production (ash-free dry mass [AFDM]) ranged from 165.9 to 233.3 g m-2 year-1, and varied between seasons. Production was lower during the cool dry northeast monsoon, when water temperatures might have limited growth, but fast growth and recruitment of multiple cohorts were possible throughout much (7-10 months) of the year and especially during the warm, wet southwest monsoon. The diet, as revealed by stomach-content analysis, consisted mainly of detritus and macrophytes, and was broadly consistent among habitats despite considerable variation in the composition and cover of aquatic plants. Apple snail annual production was >10 times greater than production estimates for other benthic macroinvertebrates in Hong Kong (range 0.004-15 g AFDM m-2 year-1, n = 29). Furthermore, annual production estimates for three apple snail populations (i. e. >230 g AFDM m-2 year-1) were greater than published estimates for any other freshwater snails (range 0.002-194 g AFDM m-2 year-1, n = 33), regardless of climatic regime or habitat type. High production by P. canaliculata in Hong Kong was attributable to the topical climate (annual mean ~24°C), permitting rapid growth and repeated reproduction, together with dietary flexibility including an ability to consume a range of macrophytes. If invasive P. canaliculata can monopolize food resources, its high productivity indicates potential for competition with other macroinvertebrate primary consumers. Manipulative experiments will be needed to quantify these impacts on biodiversity and ecosystem function in wetlands, combined with management strategies to prevent further range extension by P. canaliculata. © Springer Science+Business Media B.V. 2009.published_or_final_versionSpringer Open Choice, 01 Dec 201

Monsoons and habitat influence trophic pathways and the importance of terrestrial-marine linkages for estuary sharks

Tropical estuaries often receive enhanced fluxes of terrestrial derived organic matter and phytoplankton during the wet season, and such monsoonal events may significantly influence the trophic dynamics of these systems. This study examined spatio-temporal terrestrial-marine linkages in a tropical estuary, the Pearl River Estuary (PRE), southern China, by investigating trophic pathways leading to estuary sharks. We investigated spatial (inshore vs. offshore) and seasonal (wet vs. dry season) variation in the relative importance of terrestrial- and marine-derived carbon, so as to assess the contribution of detrital pathways to the pelagic spadenose shark, Scoliodon laticaudus; ontogentic changes in shark diets were also documented. Stable isotope analyses (SIA) and fatty acid (FA) profiling indicated that spadenose sharks assimilated both marine and terrestrial carbon via consumption of zooplantivorous fish and shrimps. Detrital carbon sources were more important to juvenile and pre-mature sharks at inshore locations, especially during the wet season when river discharge increased and terrestrial detritus was more abundant. Ontogenetic dietary shifts were evident: juvenile and pre-mature sharks had significantly higher levels of bacterial (detrital) FA than adults which contained more animal-derived FA. Inshore sharks, with more depleted δ13C signatures, relied more on terrestrial carbon than sharks offshore. Comparison of spadenose shark FA profiles with those of the sympatric, white-spotted bamboo shark (Chiloscyllium plagiosum)—a benthic predator that acquires detrital carbon via consumption of polychaetes and crustaceans—revealed that they made greater use of detrital carbon sources. However, spadenose sharks in the inner estuary assimilated higher proportions of terrestrial detritus (44–56%) than bamboo sharks (31–45%). The importance of terrestrial detritus for both shark species demonstrated the important contribution of terrestrial detritus to both pelagic and benthic food webs in the PRE. Terrestrial-marine linkages are therefore of great significance, particularly during the wet season, in this estuarine system, which serves as feeding and nursery grounds for both shark species, and trophic subsidies from land are likely to be important for marine predators in other tropical estuaries. Read More: http://www.esajournals.org/doi/abs/10.1890/ES11-00276.1published_or_final_versio

Effects of the trawling ban on the diversity of demersal crustaceans (orders: decapoda and stomatopoda) in the marine environment of Hong Kong, South China

Oral PresentationFisheries & Marine Resources ManagementBottom trawling has been demonstrated to be one of the most destructive fishing methods to marine benthic communities. Since the 1970s, marine fishery resources in Hong Kong, especially large predatory species, have been overexploited by non-selective fishing gears including bottom and pelagic trawlers. This fishing down the trophic level has resulted in a benthic ecosystem primarily dominated by small herbivorous and omnivorous fishes and crustaceans. To mitigate such impacts, the Government of the Hong Kong Special Administrative Region has implemented a territory-wide trawling ban in local waters since 31 December 2012. This study aims to investigate whether crustacean resources, in particular of the orders Decapoda and ...postprin

Explicit solutions for second order operator differential equations with two boundary value conditions

AbstractBoundary value problems for second order operator differential equations with two boundary value conditions are studied. Explicit expressions of the solutions in terms of data problems are given. By means of the application of algebraic techniques, analogous expressions to the ones known for the scalar case are obtained