Heterotrophic bacteria in Long Island Sound

Correlated with a study of heterotrophic bacteria from cultures of larval bivalve molluses, bacteria were studied from the water column over an oyster bed in Lont Island Sound, USA. Samples taken biweekly for 1 year showed bacterial densities ranging from 1.2x10³/ml in summer to 3.8x10⁴/ml in winter. Variation in seasonal density mirrored that of phytoplankton. Gram-negativ rods constituted 99% of the isolate. Eight genera were identified, but 92.3% of these were Achromobacter, Flavobacterium, and Pseudomonas. Pseudomonads dominated the summer flora, whereas flavobacteria were most abundant in spring. Types varied seasonally, but proteolytic, lipolytic, and amylolytic activity appeared independent of season.     

Seasonal growth of the giant kelp Macrocystis pyrifera in New Zealand

The seasonal growth pattern of Macrocystis pyrifera (L.) C. Agardh in New Zealand was determined from measurements of blade-elongation rates between March 1986 and December 1987. Growth rates remained relatively constant throughout most of the year, but declined significantly during the summer months. Seawater nitrate levels had a marked seasonal cycle, with concentrations of 0.3 μM detected in summer. The timing of the decline in internal nitrogen concentrations varied for different-aged blades, but occurred ∼1 mo after the decrease in seawater nitrate concentrations. Sufficiently high irradiance levels and seawater nutrient concentrations support active growth for most of the year, but growth is nutrient-limited during summer. No carbon accumulation during summer was observed. Between March and August 1988, growth estimates were also derived from node-initiation rates and stipe-elongation rates to permit comparisons with previous studies from the northern and southern hemispheres. Direct comparisons of the three growth parameters determined for non-terminated canopy and sub-surface fronds were used to assess possible differential resource allocation in the two frond classes. Received: 16 May 1997 / Accepted: 28 May 1997     

Localized defecation by pike: a response to labelling by cyprinid alarm pheromone?

Fathead minnows (Pimephales promelas) that have never encountered a predatory pike (Esox lucius), are able to detect conspecific alarm pheromone in a pike's diet if the pike has recently consumed minnows. It remains unclear how this minnow alarm pheromone is secreted by pike and if a pike is able to avoid being labelled as a potential predator by localizing these cues away from its foraging range. The first experiment determined that minnow alarm pheromone is present in pike feces when pike are fed minnows. Individual fathead minnows exhibited a fright response to a stimulus of pike feces if the pike had been fed minnows, but not if the pike had been fed swordtails, which lack alarm pheromone. Individual minnows also exhibited a fright reaction to alarm pheromone in the water (which contained no feces) housing pike which had been fed minnows, suggesting that alarm pheromone is also released in urine, mucous secretions and/or via respiration. The second experiment determined that test pike spent a significantly greater proportion of time in the home area of the test tanks (i.e. where they were fed) but the majority of feces were deposited in the opposite end of the test tank. By localizing their defecation away from the home or foraging area, pike may be able to counter the effects of being labelled as a predator by the alarm pheromone of the prey species.     

Inorganic nitrogen metabolism in marine bacteria: The intracellular free amino acid pools of a marine pseudomonad

The marine pseudomonad bacterium PL₁ contains an intracellular pool of free amino acids which consist mainly of glutamate with small amounts of glutamine and aspartate when grown in a nutrient medium containing 0.2 M NaCl. When the NaCl concentration of the growth medium is increased to 0.8 M, proline becomes a major component of the intracellular pool together with glutamate—at this molarity and under suitable nutrient conditions these amino acids comprise 20% of total bacterial amino acid nitrogen. When grown in a nutrient growth medium containing a constant level of NaCl, the intracellular pool size can vary by a factor of 4 depending on the concentration of carbon and nitrogen in the medium. Experiments show that the amino acid pool can act as a nitrogen reserve but has little function as a carbon reserve. At high NaCl concentrations there is a marked dependence for growth on the presence of sufficient potassium in the medium. However, no correlation between K⁺ and glutamate concentration in either nitrogen or K⁺-limited cultures has been found. None of the enzymes associated with glutamate biosynthesis was influenced by NaCl levels between 0.2 and 0.5 M. Neither Na⁺ or K⁺ stimulated the activity of these enzymes when tested in vitro.     

Using the expert model PERPEST to translate measured and predicted pesticide exposure data into ecological risks

An important topic in the registration of pesticides and the interpretation of monitoring data is the estimation of the consequences of a certain concentration of a pesticide for the ecology of aquatic ecosystems. Solving these problems requires predictions of the expected response of the ecosystem to chemical stress. Up until now, a dominant approach to come up with such a prediction is the use of simulation models or safety factors. The disadvantage of the use of safety factors is a crude method that does not provide any insight into the concentration–response relationships at the ecosystem level. On the other hand, simulation models also have serious drawbacks like that they are often very complex, lack transparency, their implementation is expensive and there may be a compilation of errors, due to uncertainties in parameters and processes. In this paper, we present the expert model prediction of the ecological risks of pesticides (PERPEST) that overcomes these problems. It predicts the effects of a given concentration of a pesticide based on the outcome of already performed experiments using experimental ecosystems. This has the great advantage that the outcome is more realistic. The paper especially discusses how this model can be used to translate measured and predicted concentrations of pesticides into ecological risks, by taking data on measured and predicted concentrations of atrazine as an example. It is argued that this model can be of great use to evaluate the outcome of chemical monitoring programmes (e.g. performed in the light of the Water Framework Directive) and can even be used to evaluate the effects of mixtures.     

Pacific harbor seals (<Emphasis Type="Italic">Phoca vitulina</Emphasis>) and salmon: genetics presents hard numbers for elucidating predator-prey dynamics

We used a PCR-based species test and microsatellite genotyping to determine salmonid species composition and quantity of Chinook among Pacific harbor seal (Phoca vitulina) prey. Tests were applied to DNA extracted from all salmonid bones recovered from scat (fecal) samples. Condition of bone samples and quantity of DNA varied substantially. Although DNA extraction and species identification was only successful for just over half of the bone samples, 93% of all scat samples had bones that were identified to species. Most often only a single salmonid prey species was evident within a scat sample (39% exclusively coho and 46% exclusively Chinook) but 13% contained bones from more than one species of salmonid. For scat samples that contained Chinook bones, 68% had skeletal remains from the same fish and 32% had bones from more than one individual Chinook, varying in number from two to four individuals per scat. In one case, bones from one individual Chinook were recovered in three different scat samples.     

Is there a “sound window” for primate communication?

Summary It has long been asserted that habitat acoustics can determine the frequency band bestadapted for long-range communication, but the generality and validity of measurements claiming to demonstrate a window of best frequencies have recently been questioned. We report the discovery of a prominent sound window in Kenyan rain forest in a study that is free of methodological difficulties. Our results allow us to calculate the range advantage attained by an animal vocalizing within the sound window, and show that sound windows can be a potent factor for the evolution of primate communication.     

Asynchronous deposition of dense skeletal bands in Porites lutea

Alternate dense and less-dense skeletal bands in massive corals have been used for many years to record the history of growth in species such as Porites lutea and Montastrea annularis, based on the assumption that one dense band and one less-dense band is equivalent to a year's growth. This report demonstrates that specimens of Porites lutea Edwards and Haime (collected from the same neighbourhood in Phuket, Thailand, from November 1983 through November 1984) produce skeletal bands asynchronously and that one year's growth in corals from certain sites may regularly consist of four bands of varying density. The annual banding pattern observed at all sites includes the deposition of a dense band in response to high sedimentation loads and, probably, reduced light levels.     

Stereophotography for the field biologist: measurement of lengths and three-dimensional positions of free-swimming sharks

A stereophotographic technique for determining size and relative position of free-swimming sharks is described and illustrated for schooling scalloped hammerhead sharks (Sphyrna lewini). The method yields total length and nearest-neighbor, interindividual distance; and each of these dimensions is expressed as a function of the shark's distance into a school on the vertical and horizontal planes. Stereopairs of photographs were taken by an aligned, beam-mounted pair of cameras (Nikonos III). The scale to determine the length of a shark from the paired photographic images was obtained from the horizontal displacement between the images. Displacement was correlated with optical axis separation from photographs of a scaled staff at known distances from the camera. Image dimensions on the photographs were measured by projecting a scale onto the stage through a camera lucida. The precision of repeated measurements of a 50 cm section of a scaled staff at increasing distances from the cameras of 2, 4, and 8 m was ±5.0%. Lengths of the sharks ranged from 109 to 371 cm, with a median of 178 cm, for 3 offshore sites in the Gulf of California during July and August 1979. At one site, El Bajo Gorda, lengths increased with both distance from the camera and distance into the group; in contrast, the interindividual distances (head-to-head) did not vary with distance into the group and possessed a median of 232 cm.