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Aspects of the reproductive biology of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana, were studied from September 2014 to August 2015. The current study was aimed at providing information useful for managing the mussel fishery in this locality and also that would form the basis for designing appropriate culture methods for the species. Microscopic examination of fresh smears of gonadal material, as well as histological preparations of the gonad, were used to study the sexuality and breeding pattern of the species. Monthly gonadal and condition indices were also determined. Perna perna exhibited gonochoristic sexuality with a sex ratio of approximately 1:1 throughout the study period. Sexes were identifiable at shell lengths of 15.0–19.9 mm. Five stages of gonadal development were identified in both sexes. Gametogenic activity was continuous throughout the year, with two major spawning activities, from April to June and from August to December. These periods coincided with the major and minor rainy seasons, respectively, as well as the major upwelling period in August. Condition indices suggest that the mussels were in better condition for harvesting in March and August prior to the major spawning events. 相似文献
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Dust in the Wind: Long Range Transport of Dust in the Atmosphere and Its Implications for Global Public and Ecosystem Health 总被引：4，自引：0，他引：4
Movement of soil particles in atmospheres is a normal planetary process. Images of Martian dust devils (wind-spouts) and dust
storms captured by NASA's Pathfinder have demonstrated the significant role that storm activity plays in creating the red
atmospheric haze of Mars. On Earth, desert soils moving in the atmosphere are responsible for the orange hues in brilliant
sunrises and sunsets. In severe dust storm events, millions of tons of soil may be moved across great expanses of land and
ocean. An emerging scientific interest in the process of soil transport in the Earth's atmosphere is in the field of public
and ecosystem health. This article will address the benefits and the potential hazards associated with exposure to particle
fallout as clouds of desert dust traverse the globe.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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Russell C. Hedberg II Arielle Hesse Doug Baldwin Jase Bernhardt David Pahl Retchless Jamie E. Shinn 《The Professional geographer》2017,69(1):107-116
Recent debates about the state of geography raise valuable questions about how the discipline can and should change in response to shifting institutional realities. Focusing on the breadth and interdisciplinarity of geography, these discussions often overlook the role of pedagogy—particularly graduate training—in adapting the discipline to new institutional landscapes. Drawing on experiences as current and recent geography doctoral students, we identify institutional seedlings of opportunity that can be cultivated toward a spectrum of alternative doctoral training models. These alternatives offer significant opportunities to better prepare early-career geographers for success and to solidify geography's position as a leader in interdisciplinary research. 相似文献
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Coral reef recovery in Florida and the Persian Gulf 总被引：1，自引：0，他引：1
Long-term observations and study of coral reef destruction by hurricanes in the Florida Keys show, surprisingly, that although
corals are devastated on a grand scale during storms, recovery is rapid. Recovery occurs because of the widespread scattering
of live fragments, many of which become growth sites of new colonies. Reef recovery from death by chilling in the Persian
Gulf was well under way when last observed, but it is not yet known if the recovery rate was as rapid as recovery from the
storm destruction in Florida. Recovery from death by chilling requires settlement of transported coral larvae and a substrate
suitable for larval attachment. Such resettlement is subject to the effects of currents, predators, pollution, and competition
for substrate.
A growth rate of 10 cm per year combined with geometrical progression of branch formation accounts for rapidAcropora cervicornis recovery. Although calculated coral proliferation seems unusually high, it has been confirmed by serial underwater photographs
spanning ten years. More precise measurements of growth and branching are needed, along with growth data for other common
reef-building corals. Such data would be useful for predicting standing crop of a restocked or transplanted reef. 相似文献
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Brian King Jamie E. Shinn Kayla Yurco Kenneth R. Young Kelley A. Crews Meyer 《The Professional geographer》2019,71(1):29-38
Research within geography and related disciplines has directed much attention to the coupled interactions between social and ecological systems. These studies have usefully analyzed the multifaceted, temporal, and scalar dimensions of human–environment interactions and how future environmental change will continue to challenge human resource needs. Political ecology research has also made contributions in this regard, particularly by emphasizing livelihood systems, impacts of conservation and development, agricultural production, and environmental governance. Yet although political ecology research has contributed to socioecological systems scholarship, much of this work has been situated within dryland environments or marine ecosystems that have particular biophysical features. Comparatively, wetland environments that experience dynamic flooding regimes warrant further attention from political ecology. This article engages with the findings from an ongoing research project that is evaluating the impacts of flooding variability for rural livelihoods in the Okavango Delta of Botswana. We outline some of the main findings from this work by concentrating on two themes central to political ecology: access and governance. We conclude by arguing that the Okavango Delta should be understood as a hydrosocial waterscape that encompasses a variety of socioecological relationships within the region, as well as the power relations operating at a variety of scales that both produce and govern them. 相似文献
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Seepage meters and Bernoulli’s revenge 总被引：2，自引：0，他引：2
Evaluation of seepage data from a network of 50 permanently deployed submarine seepage meters, specially construc ted from
fiberglass, indicates that the devices artificially advect (Bernoulli effect) shallow ground water. Reverse flow into the
rock was not observed even when adjacent piezometers installed 2-m to 20-m below the rock-water interface in dicated negative
groundwater heads. Quantitative testing of five different designs, including conventional end-of-oildrum designs, indicates
that meters presenting positive relief on the sea floor are subject to the Bernoulli effect when placed in areas where there
are waves and/or currents. Advection does not appear to be caused by flexing of the collection bags. 相似文献