The importance of periodic droughts for maintaining diversity in the freshwater environment

Whereas some species may rely on periodic drought conditions for part of their life histories, or have life strategies suited to exploiting the habitat or changed environmental conditions that are created by drought, for other organisms it is a time of stress. Periodic drought conditions therefore generate a series of waves of colonization and extinctions. Studies on lowland wet grassland, in winterbournes and in the toiche zone of both ponds and rivers, also demonstrate that different organisms are competitively favoured with changing hydrological conditions, and that this process prevents any one species from overwhelming its competitors. Competitive impacts may be inter- and intraspecific. It is therefore apparent that the death of organisms such as adult fish during severe drought conditions, though traumatic for human onlookers and commercial interests, may be merely a regular occurrence to which the ecosystem is adapted. The variability of climatic conditions thereby provides a direct influence on the maintenance of biological diversity, and it is this very biodiversity that provides the ecosystem with the resilience to respond to environmental changes in both the short and the longer term.

Periodic autoregressive moving average models for the analysis of streamflow [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Streamflow values show definite seasonal patterns in their month-to-month correlation structure. The structure also seems to vary as a function of the type of stream (coastal versus mountain or humid versus arid region). The standard autoregressive moving average (ARMA) time series model is incapable of reproducing this correlation structure. ... A periodic ARMA time series model is one in which an ARMA model is fitted to each month or season but the parameters of the model are constrained to be periodic according to a Fourier series. This constraint greatly reduces the number of parameters but still leaves the flexibility for matching the seasonally varying correlograms.

Coastal engineering investigation at Jupiter Inlet, Florida

A fixed-bed hydraulic model of Jupiter Inlet, Florida, was constructed for the purpose of testing measures designed to remedy problems of sediment erosion and deposition in the inlet area. Both tide-induced flows as well as waves were simulated in the model which was built on an undistorted scale of 1:49. Model verification was based on prototype measurements of waves, tides and currents. Results have been interpreted in terms of the influence of various proposed remedial schemes on flow velocity magnitude, distribution and wave height at various locations within the study area. A stability parameter has been utilized for evaluating the degree of sediment erosion or deposition at a given location. Various structural solutions were examined in the model. It is proposed that, in the initial phase of solution implementation, sediment removal/nourishment methods be used primarily to mitigate the existing problems. New structures, as per model test results, should be installed under subsequent phases, only if sediment management procedures do not prove to be adequate. The currently followed procedure of periodic sand trap dredging may be extended to include the new dredging/nourishment requirements. (PDF contains 245 pages.)

Olympic Coast National Marine Sanctuary: Proceedings of the 1998 Research Workshop, Seattle, Washington

The Olympic Coast National Marine Sanctuary (OCNMS or Sanctuary) planned and organized the 1998 Research Workshop as part of its mission to protect and improve understanding of its marine resources through research and education programs. The Sanctuary is also mandated to coordinate and facilitate information exchanges and sponsors periodic research workshops to that end. The goals of the 1998 Research Workshop were as follows: A. Highlight and prioritize research needs for the Sanctuary relative to the development of a framework for a five-year research plan; B. Build on results from the Olympic Coast Marine Research Workshop of 1996; C. Present recent/ongoing research; D. Share multi-disciplinary information; E. Select priority sites for multi-disciplinary studies; and F. Promote student participation and research. (PDF contains 93 pages.)

Sexual Reproduction and Early Development in the Estuarine Sea Anemone, Nematostella vectensis Stephenson, 1935

This dissertation: 1) determines the factor(s) responsible for spawning induction in NematosteJla vectensis; 2) isolates, describes, and documents the source of jelly from egg masses of N. vectensis; and 3) describes N. vectensis' early development. Namatostella vectensis were maintained on a 7-day mussel feeding/water change regime over 159 days. Within 36 hours of mussel feeding/water change. 69.1% of females and 78.5% of males spawned reliably. Through manipulation of feeding, water change, oxygen and nitrogenous waste concentrations, spawning induction was found to be triggered by the oxygen concentration associated with water change, and not by feeding. Ammonia, anemones' major waste product, inhibited this induction in a concentration-dependent manner. Female N. vectensis release eggs in a persistent jellied egg mass which is unique among the Actiniaria. The major component of this egg mass jelly was a positive periodic acid-Schiffs staining, 39.5-40.5 kD glycoprotein. Antibodies developed in rabbits against this glycoprotein bound to jelly of intact egg masses and to granules (~ 2.8 IJm in diameter) present in female anemone mesenteries and their associated filaments. Antibodies did not label male tissues. Nematostella vecfensis embryos underwent first karyokinesis -60 minutes following the addition of sperm to eggs. Second nuclear division took place, followed by first cleavage, 90-120 minutes later. Each of the 4 blastomeres that resulted from first cleavage contained a single nucleus. Arrangement of these blastomeres ranged from radial to pseudospiral. Embryonic development was both asynchronous and holoblastic. Following formation of the 4-cell stage, 71% of embryos proceeded to cleave again to form an 8-cell stage. In each of the remaining 29% of embryos, a fusion of from 2-4 blastomeres resulted in 4 possible patterns which had no affect on either cleavage interval timing or subsequent development. The fusion event was not due to ooplasmic segregation. Blastomeres isolated from 4-celled embryos were regulative and developed into normal planula larvae and juvenile anemones that were 1/4 the size of those that developed from intact 4-celled embryos. Embryos exhibiting the fusion phenomenon were examined at the fine structural level. The fusion phenomenon resulted in formation of a secondary syncytium and was not a mere compaction of blastomeres.

Biological production in the Eastern Pacific Ocean

ENGLISH:The present paper is principally concerned with the geographic distribution of the standing crop and production of phytoplankton at the surface of the eastern Pacific, east of 130°W and between 10°N and 33°S, as reflected by recently collected data. In addition we discuss some of the more obvious, general relationships among thermocline topography, nutrient concentration, and the various trophic levels from primary production to fish production. The limited data do not allow a seasonal study. We have therefore mapped all of the data together regardless of the time of collection, but do not wish to imply that the physical, chemical and biological system is without seasonal or periodic change. SPANISH:Como lo reflejan los datos recientemente recolectados, el presente trabajo está dedicado principalmente a la distribución geográfica de las cosechas estables y a la producción del fitoplancton en la superficie del Pacífico Oriental, al este de los 130°W y entre los 10°N y 33°S. Además discutimos algunas de las relaciones generales más obvias entre la topografía de la termoclina, la concentración de los nutrientes, y los varios niveles tróficos, desde la producción primaria hasta la producción de los peces. Los datos limitados no permiten un estudio estacional. Por lo tanto, hemos combinado todos los datos no tomando en cuenta el tiempo de la recolección, pero no queremos implicar que no existen cambios estacionales o periódicos en el sistema físico, químico y biológico.