In situ grazing rates of deep-sea benthic boundary-layer zooplankton

In situ grazing rates of mixed assemblages of deep-sea benthic boundary-layer zooplankton were measured in July 1983 at a site in the North Atlantic Ocean at 2 175 m depth using a short-term radioisotope-uptake method. Zooplankton were collected with an opening-closing net system from the bottom 1 m of the ocean and incubated in situ with mixed tritiated amino acids in special cod-end chambers. Incubations were terminated at depth by the addition of MS-222. Radioisotope uptake beyond that of dead controls was shown by both the zooplankton and particulate fractions. Grazing rates in the deep-sea experiments were surprisingly high, being comparable to wintertime Narragansett Bay zooplankton grazing rates determined in a separate series of laboratory experiments. These laboratory experiments also documented nonparticle-associated uptake of dissolved amino acids by Narragansett Bay zooplankton, but the importance of this in the deep sea is unknown. The deep-sea benthic boundary layer may be a region of elevated rates and activity because of its higher particulate concentrations, and our experiments may also have measured maximum rather than average rates.     

Description and use of an improved method for determining estuarine zooplankton grazing rates on phytoplankton

A method of rapidly determining zooplankton grazing rates on natural mixed phytoplankton populations using ¹⁴C is described. The method simplifies the design of grazing experiments as the grazing time can be kept short enough to prevent recycling of the isotope, and growth of the phytoplankton substrate. Very high specific activity, ¹⁴C-labelled phytoplankton concentrated either by centrifugation or sieving, may be used either as the sole grazing substrate, or as a tracer in natural mixed phytoplankton. Zooplankton, confined in glass jars at either ambient, or higher than ambient concentrations, are permitted to feed on the phytoplankton for periods of 30 min and 2 h, and are then separated by sieving. The zooplankton community grazing rate, or, if the samples are sorted into species, the individual species grazing rates, can be determined after scintillation counting of the zooplankton. The rate of appearance of ¹⁴C-labelled phytoplankton in the zooplankton is an estimate of the grazing rate, and the slope of the line joining the grazing rates at various phytoplankton concentrations gives an estimate of the grazing rate constant for the zooplankton population. The method provides a quick way of obtaining both zooplankton population, and individual species grazing rates on natural mixed phytoplankton. In two experiments, labelled phytoplankton was used as the sole grazing substrate in concentrations ranging between 0.4 and 5 times ambient levels. Grazing rate constants, for net-caught zooplankton concentrated to 46 times (Experiment 1) and 28 times (Experiment, 2) ambient estuarine levels were-0.14and-0.12 of the phytoplankton standing stock per day, respectively. There was a linear increase in the amount of phytoplankton grazed with an increase in phytoplankton concentration up to four times ambient phytoplankton levels. When tracer amounts of labelled phytoplankton were added to samples containing both phytoplankton and zooplankton at ambient concentrations the grazing rate constants were-0.28 and-0.42 of the phytoplankton standing stock per day. We conclude that zooplankton grazing was the major control factor of phytoplankton population size during October–November 1975 in South West Arm, Port Hacking, near Sydney, Australia.     

A new method to determine in situ growth rates of decapod shrimp: a case study with brown shrimp Crangon crangon

Shrimps are economically and ecologically very important, yet a lack of ageing techniques and hence unknown growth rates often impairs analytical assessments and management. A new method for the determination of in situ growth rates of shrimps is presented, based on dry weight condition. Since this index oscillates from low values directly after moult to highest values prior to moult in constantly feeding shrimp, the lowest observed pre-moult condition followed by a moult was introduced as a reference value to separate growing and starving individuals in field data. Experiments with Crangon crangon confirmed that (1) post-moult condition varies in a narrow physiologically optimal range, regardless of recent growth increments, and (2) dry weight condition prior to moult is closely related to the subsequent length increment. The method was applied to estimate growth increments from in situ dry weight condition data of C. crangon. The new method can easily be applied to other related species, since the required data can be obtained from very simple short-term experiments.     

Coral weight increment in situ. A new method to determine coral growth

An underwater weighing apparatus is described. This consits basically of a float, the buoyancy of which is neutralized by a known amount of lead weights. The standard error of the method is ±0.1g. The entire weighing procedure takes place on the reef using SCUBA diving gear. The advantages are that the animals are not harmed by experimental treatment, and that the pure calcium-carbonate increment is registrated. Some results obtained by this method show growth of Montastrea annularis and Madracis mirabilis.     

Selective grazing by zooplankton populations in Southampton Water

Experiments were made with natural populations of both zooplankton and phytoplankton from Southampton Water (England), using an electronic particle counter to measure grazing effects. What appear to have been large differences within and between experiments in size of particles selected are shown to have been mainly a result of variations in total amout of grazing. When this was taken into account it was found that there was no difference in size of particles selected most strongly whether the zooplankton was dominated by copepods or smaller cirripede nauplii. This can be accounted for by similarities in the setous feeding appendages of these two forms. It is suggested that similarity in particle selection would lead to competition between the two grazers if they were not separated seasonally.     

In situ filtering and ingestion rates of deep-sea benthic boundary-layer zooplankton in the Santa Catalina Basin

In situ rates of filtration, particulate ingestion, and carbon ingestion of deep-sea benthic boundary-layer zooplankton were determined in December 1984 in the Santa Catalina Basin, at 1 300 m depth in the California Borderland, by a short-term radioisotope-incorporation technique. Zooplankton were collected at 1 or 50 m above the bottom with an opening-closing net system on a submersible, and incubated at depth with labelled amino acids in special cod-end chambers. Concentrations of particulate material and particulate organic carbon in the ambient water were also measured. The zooplankton had a median weight-specific filtration rate of 12.4 ml (mg dr. wt)^-1 h^-1 and a median carbon ingestion rate of 5.4 g C (mg dr. wt)^-1 h^-1. Filtration rates were not significantly different from those in similar experiments in the north Atlantic at 2 175 m depth or Narragansett Bay in the winter, although the medians of the deep-sea experiments were lower than for the Bay. In the Santa Catalina Basin, rates from experiments at 1 m above the bottom in more turbid water were not significantly different from those at 50 m above the bottom in clearer water. These deep-sea benthic boundary-layer zooplankton may have the potential to respond to food pulses, and their relatively high ingestion rates suggest that they could have significant effects on particulate, chemical, and bacterial processes in the near-bottom water column.     

The use of measurable coefficients in process formulations—zooplankton grazing

This paper redefines a construct previously used to model phytoplankton—zooplankton interactions in such a way as to permit the use of measurable quantities as contruct coefficients. The new construct can use unaltered values of the half-saturation constant for zooplankton grazing on total available food (k_s) and the minimum food concentration necessary to stimulate effective feeding (BMIN) reported in the literature. Typical values for these coefficients are 0.1–15 and 0.016–0.19, respectively.     

Discriminating zooplankton assemblages through multivariate methods: A case for a tropical polluted harbour and Bar-built estuary

A comparative study (June-July 2001) on zooplankton community structure amid polluted conditions in a stagnant harbour and relatively unaffected tidal estuary near Visakhapatnam, on the east coast of India, revealed a marked disparity in species composition and abundance. While the harbour supported a rich population of calanoids (46.4%), the estuary sustained mostly cyclopoids (55.2%). Univariate and multivariate techniques (species diversity, clustering, non-metric multi-dimensional scaling and one-way ANOSIM) revealed the existence of two differing zooplankton assemblages and associated water quality (similarity 50.6%). While the estuary is typified by high amounts of dissolved silica (67.4 ± 17.7 μmol l^-1) linked with monsoon influx, the harbour waters revealed abnormal levels of phosphate (40.9 ± 9.2 μmol l^-1) and nitrate (15.3 ± 5.41 μmol l^{- 1}) suggestive of intense eutrophication, caused by the discharge of fertilizer-factory waste and domestic sewage. On the basis of routines (e.g. BVSTEP, SIMPER) implemented in Plymouth Routines in Multivariate Ecological Research, it was possible to demonstrate that while species such as Oithona rigida, Oithona brevicornis, crustacean nauplii, gastropod veligers, Acartia spinicauda, and Acartia centrura played a key role in discriminating the zooplankton assemblage in the estuary, Acrocalanus spp. (mainly Acrocalanus gracilis) played a keyed role in harbour waters. Canonical Correspondence Analysis revealed species-environment relationships; for example, while the distribution of Oithona spp. and its associates in the estuary corresponded intimately with high silicate, temperature, and low salinity, it was high salinity, phosphate, and nitrate in the harbour channel that supported a different assemblage of copepods dominated by calanoids.     

Diel fluctuation in zooplankton grazing rate as determined from the downward vertical flux of pheopigments

The diel grazing activity of zooplankton was measured at a single study site in a temperate fjord, Dabob Bay, Washington, USA at several periods during spring, summer and fall of 1979–1981. Pheopigments were used as an indicator of herbivorous zooplankton activity. The downward vertical flux of pheopigment-containing fecal pellets was measured with sediment traps deployed over repetitive 4 h periods. Experiments were run for 24 to 36 h. A maximum in the flux of pheopigments was consistently noted within the euphotic zone during hours of darkness. Diel fluctuations in pheopigment flux showed amplitudes up to 29-fold. Nightly grazing activity accounted for 41 to 82% of the daily (24 h) grazing and was indirectly related to seasonal changes in daylength.Contribution No. 1405 from the School of Oceanography, University of Washington     

Numerical modelling of diel carbon production and zooplankton grazing on the Scotian shelf based on observational data

Using high resolution vertical distributions of chlorophyll and zooplankton, and field observations of photosynthetic parameters, it is shown that on the Scotian Shelf the peak in the vertical profile of primary production generally lies shallower than the chlorophyll maximum, but coincides with the peak in the vertical profile of copepods. A simple numerical model shows that the 24th carbon budget can be balanced using the best available estimates of the rate constants for phytoplankton growth, zooplankton grazing and vertical migration. This calculation is very sensitive to the size of the weight-specific ration and favors values of ～40% d^?1 for it.     

Potential effect of phytoplankton colony breakage on the calculation of zooplankton filtration rates

Substantial net production of short chains of the diatom Skeletonema costatum occurred in grazing experiments conducted with Acartia hudsonica (=A. clausi). A general model was then constructed to evaluate the influence of colony breakage during grazing on the calculation of zooplankton filtration and ingestion rates. Breakage can lead to either over-or underestimation of these rates. The magnitude of error is related to breakage probability, particle size distribution, size of the largest colonies, length of the experiment, copepod concentration and actual filtration rates. Size distributions similar to those described in the literature as manifestations of a complex selection for size and particle abundance can be generated by the grazing model under conditions of a uniform filtration rate accompanied by colony breakage. Unless the rate of breakage exceeds the rate of removal and causes net particle production, the occurrence of breakage may go undetected.     

Sinking-rate response of natural assemblages of temperate and subtropical phytoplankton to nutrient depletion

Phytoplankton assemblages were collected during spring blooms in 1982 in Washington State and in Hawaii. Sinking rate responses of these assemblages were examined under nitrate, phosphate, and silicate depletion. Ambient nutrient concentrations, chlorophyll concentrations, photosynthetic rates, sinking rates, and floristic compositions were determined. Under nutrient-replete conditions, the temperate assemblage, composed primarily of large centric diatoms, had a sinking rate of 0.96 m d^-1; sinking rates did not change appreciably over 4 d without nitrate. Without phosphate or silicate, the sinking rates remained constant for 3 d and then increased after biomass indices began to decline. These findings illustrate the potential importance of phosphate or silicate depletion to the sedimentation of spring-bloom diatom populations. The subtropical assemblage, composed primarily of diatoms, coccolithophorids, and dinoflagellates, had an initial sinking rate of 0.22 m d^-1 and did not display substantial sinking rate changes in the absence of nitrate, phosphate or silicate. Floristic data consistently showed a proliferation of pennate diatoms, which had lower settling rates than centric diatoms. Growth and sedimentation patterns indicated a competitive advantage for pennate diatom components of subtropical assemblages; this in turn may limit phytoplankton sedimentation losses in such ecosystems.     

Intertidal assemblages on artificial and natural habitats in marinas on the north-west coast of Italy

Following the progressive expansion of human populations, the number of artificial habitats is increasing in shallow waters of urbanised coastal areas. The comparison of assemblages between natural and artificial habitats is necessary to determine whether there is real loss and fragmentation of natural habitats. This study investigates the changes in intertidal assemblages caused by marinas for tourists, along exposed rocky shores on the north-west coast of Italy. Marinas, being made of transplanted boulders and by internal wave-sheltered seawalls, introduce different types of artificial habitats in a relatively small area. Intertidal assemblages on breakwaters, seawalls and adjacent rocky shores were compared at three locations, thousands of metres apart. To assess the generality of patterns through time, natural and artificial habitats were sampled at three different times, over a period of about 2 years. Data were analysed by means of multivariate and univariate analyses to test the hypotheses that assemblages and abundances of single taxa differed among habitats, consistently among locations and times of sampling. Furthermore, the variability of assemblages at the scales of tens of centimetres and metres was compared among habitats. Assemblages on seawalls were largely distinct from those on rocky shores or breakwaters. Seawalls, which supported a smaller number of species than breakwaters and rocky shores, were dominated by encrusting algae and lacked common species such as Rissoella verrucosa and Patella rustica. The abundance of main-space occupiers did not differ between breakwaters and rocky shores, but there were differences in variability of assemblages at both the spatial scales investigated. This study provides evidence for differences between intertidal assemblages supported by artificial habitats at marinas and those on adjacent rocky shores. Differences in habitat-structure (and/or wave-exposure in the case of seawalls) could explain the occurrence of distinct intertidal assemblages. Despite the nature and magnitude of these differences, varied according to the type of artificial habitat considered, neither breakwaters nor seawalls could be considered surrogates of rocky shores.Communicated by R. Cattaneo-Vietti, Genova     

企业财务危机预警判断分析方法研究

财务危机是威胁企业持续经营的根本性危机,它不是突然而至,分为潜伏期、爆发期、成长期和解决期四个阶段逐步积累过程.根据不同阶段的企业财务状况,把爱德华.阿特曼Z值计分模型和不同时期的相关财务指标结合起来,运用定量和定性相结合的分析方法,判断分析企业的财务危机的级别,从而采取相应的措施,以利于规避财务风险.     

Growth and grazing loss rates in single-celledPhaeocystis sp. (Prymnesiophyceae)

Growth and grazing loss rates of naturalPhaeocystis sp. single cells were measured using a seawater dilution technique. Measurements were performed during an intensePhaeocystis sp. bloom in the North Sea between 19 April and 5 May 1988. Experimental results yielded rapid carbon turnover rates. Population growth rates varied from 0.033 to 0.098 h^–1, grazing loss rates from 0.037 to 0.174 h^–1. From measured growth rates, average doubling rages of 1.3 doublings d^–1 were calculated. The growth rates would have resulted in maximum carbon production rates of 146 mg C m^–3 d^–1. Grazing rates increased in the course of the bloom and exceeded growth rates at the end. Grazing loss was caused primarily by microzooplankton feeding. Ciliates and heterotrophic dinoflagellates were identified as the major potential consumers of single cells ofPhaeocystis sp. at the beginning of the bloom. The grazing impact of larger microzooplankton species appeared to increase during the progressing bloom.     

Fish assemblages composition in a natural, then regulated, stream: A quantitative long-term study

This paper tests the hypothesis how effectively fish assemblage composition was shaped by local climate changes and by engineering impact in 1989. This was possible due to the monitoring protocols of the present study, which allowed estimation of the magnitude of anthropogenic changes from changes naturally occurring in nature. Fish were sampled at the end of every growing season (October) for 23 years at five contiguous sites in a stream, before (1979-1988) and after (1989-2001) regulation. In each sample, six successive electrofishing passes were used to calculate the density and mean biomass for assemblage analysis using the Zippin model. During the study, the natural, meandering stream with pools, riffles, and a moderate canopy was modified into a straight stream of uniform width and depth, stripped of all vegetation. The output layer of a self-organizing map (SOM, the artificial neural network algorithm) applied in this study for site similarity analysis was partitioned into six subclusters placed in two main clusters. Subclusters in the upper part of the SOM were occupied chiefly by regulated stream samples and those in the lower part of the SOM by natural stream samples. Subclusters in the middle position, contained both natural (19) and regulated (20) samples in nearly equal proportion. In addition, the SOM contained one subcluster with sites only from the regulated period and another with only natural sites. Differences between subclusters were attributed to differences in climate, with some differences profound. Warming of the local weather, which became most evident in the 1990s, may have resulted in changes in fish assemblages. This is shown in the SOM, in which samples from the 1980s with cold years dominate the bottom of the SOM, whereas those from the 1990s and later are at the top. Subclusters dominated by regulated or natural sites were not always significantly different when the number of species and diversity indices were considered. Clear differences between the regulated and natural samples involved qualitative characteristics and mainly concerned assemblage composition. They were also confirmed by significant IndVal values (indicator species) and neither mixed subcluster contained important species in their assemblages.     

Effects of mixing-induced irradiance fluctuations on photosynthesis of natural assemblages of coastal phytoplankton

Photosynthesis versus irradiance relations were determined from field incubations of natural assemblages of phytoplankton that were either cycled at three different rates between the surface and a depth of 5 m or kept at constant depths. Photoinhibition of photosynthesis was not observed in the bottles kept at constant depths during 3.5-h experiments. Photosynthesis versus irradiance (P-I) curves derived from bottles kept at constant depths and the irradiance time course received by each of the cycled bottles were used to predict photosynthesis within each of the cycled bottles. P-I curves derived from measurements under relatively constant irradiance accurately predicted the mean photosynthetic response of phytoplankton that experienced large fluctuations in irradiance.     

Harbours as marine habitats: hydroid assemblages on sea-walls compared with natural habitats

Sessile hydrozoans constitute a common component of marine rocky communities. We compared the hydrozoan assemblages occurring on sea-walls of commercial harbours with those on natural rocky cliffs along the southern Iberian Peninsula, to identify differences in the multivariate structure of the assemblages and species richness. Harbour hydroid assemblages significantly differed from natural ones mainly due to their qualitative composition. Medusa-less taxa, optimized for low dispersal and long-term persistence on the substratum, are barely represented in harbours, but abundant at natural sites. “Port species” assemblages were composed of (1) small, short-living species with typical opportunistic characteristics; (2) cosmopolitan large-size taxa, significantly represented both in harbours and in natural habitats; (3) non-indigenous species. Contrarily to the expected lower richness of communities in confined areas, our results demonstrate that richness of hydroid assemblages in harbours is comparable to that of natural habitats.     

Estimation of Arctic copepod grazing rates in vivo and comparison with in-vitro methods

Gut evacuation rates were measured in Calanus hyperboreus and C. glacialis from two stations in Jones Sound, Northwest Territory (NWT) and one station in an Ellesmere Island Fjord during late summer of 1984. Gut content decreased exponentially with a rate constant, that, for Stage V C. glacialis at least, was independent of food type and time of day. Gut filling rates were measured in Stage V C. glacialis in the light and in the dark, at noon and midnight. Nighttime gut filling rates were very similar for both light intensities, and also similar to the daytime rate in the dark, whereas the daytime rate in the light was much lower. Ingestion rates were calculated for these latter experiments, including a rate term for defecation, and these results were compared to the values obtained from the observations of gut filling rates in vivo as reported in Head et al. (1985) and from long-term (2–3 d) bottle incubations as reported in Head et al. (in press). The following points were made: (1) in-vivo and in-vitro ingestion rates were very close if appropriate in-vitro experimental conditions were used with respect to light intensity and time of day; (2) copepods could fill their guts at a rate apparently higher than their normal nocturnal ingestion rate; and (3) the calculated rations were dependent on the shape of the observed diurnal feeding patterns.     

Restoring native fish assemblages to a regulated California stream using the natural flow regime concept

We examined the response of fishes to establishment of a new flow regime in lower Putah Creek, a regulated stream in California, U.S.A. The new flow regime was designed to mimic the seasonal timing of natural increases and decreases in stream flow. We monitored fish assemblages annually at six sample sites distributed over approximately 30 km of stream for eight years before and nine years after the new flow regime was implemented. Our purpose was to determine whether more natural stream flow patterns would reestablish native fishes and reduce the abundances of alien (nonnative) fishes. At the onset of our study, native fishes were constrained to habitat immediately (<1 km) below the diversion dam, and alien species were numerically dominant at all downstream sample sites. Following implementation of the new flow regime, native fishes regained dominance across more than 20 km of lower Putah Creek. We propose that the expansion of native fishes was facilitated by creation of favorable spawning and rearing conditions (e.g., elevated springtime flows), cooler water temperatures, maintenance of lotic (flowing) conditions over the length of the creek, and displacement of alien species by naturally occurring high-discharge events. Importantly, restoration of native fishes was achieved by manipulating stream flows at biologically important times of the year and only required a small increase in the total volume of water delivered downstream (i.e., water that was not diverted for other uses) during most water years. Our results validate that natural flow regimes can be used to effectively manipulate and manage fish assemblages in regulated rivers.