The substrate bin—a new sampling device for studying diel vertical migratory movements on to and off lake sediments

The substrate bin, used to study diel migratory movements of the copepod Pseudodiaptomus hessei on to and off bottom interfacial areas is described. It consists essentially of a transparent Perspex box open at its upper end and supported upright within a metal framework. A lid, hinged along one face of the open end of the bin, opens and closes automatically through a simple system of levers as the apparatus is lowered on to or raised off a solid substrate. The apparatus is lowered on to the lake bed where it opens. Diel movements on to or off the shallow layer of bottom substrate enclosed within the bin can be examined by retrieving bins serially at different times. Using this apparatus in conjunction with standard net sampling techniques, clear evidence for an alternation of benthic and pelagic phases during diel cycles was obtained. Notwithstanding an apparent oversampling of the benthic component, the magnitude of which cannot be defined precisely, it is concluded that the apparatus provides a simple and reliable method of sampling.     

Nutritional suitability of some uni-algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others

• 1 Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono-specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl^?1).
• 2 All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.
• 3 Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen-fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.

     

Oxygen consumption in Caridina nilotica (Decapoda: Atyidae) in relation to temperature and size

SUMMARY. The oxygen consumption of shrimps ranging from 1 to 30 mg dry mass was determined at 18, 24 and 30°C using a continuous flow recording respirometer based upon a Clark-type oxygen electrode. Respiration (ascribed to routine metabolism) is described by the power curve: R = a M^b , ( R =μg O₂ h⁻¹, M = mg dry mass), which gives values of a = 1.632, 2.564 and 4.181, and b = 0.800, 0.898, and 0.793, at 18, 24 and 30°C respectively. The single expression, R = 0.008 T ^1.829 M ^0.830 provides a reasonable prediction of respiration as a combined function of shrimp size ( M ) and temperature (T, °C). Using an energy equivalent of 14.14 J mg O₂⁻¹ estimates of the energy requirements ( E , J h⁻¹ 10⁻³) of routine metabolism are given by the expression: E = 0.115 T ^1.829 M ^0.830.
Variability in oxygen consumption values between individuals is discussed and the observations on C. nilotica are compared with other crustacean studies.     

Photoregulation of hypocotyl growth: geotropic evidence for the operation of two photosystems

Abstract. The rate of curvature of etiolated cress ( Lepi-dium sativum L. ) hypocotyls in response to gravity (negative geotropism) was retarded by red or blue light; far-red irradiation was without effect. The timing of the irradiation period in relation to the presentation for geostimulus markedly affected the response. When seedlings were irradiated during the 1–2 h period of geostimulus, blue light was more effective than red at retarding curvature; when seedlings were irradiated prior to geostimulus, only red light affected geocurvature. These results are interpreted as a further example of the kinetically distinct effects of red and blue light on hypocotyl development. Blue light elicited a rapid, immediate response effective only during the period of irradiation; red light induced a response characterized by a lag period and persistence in subsequent darkness. Etiolated mustard seedlings showed similar responses to light and gravity. The results are discussed in relation to the possibility that two photosystems operate in hypocotyl growth.     

Photosynthetic Electron Transport in Shoots of Sitka Spruce from Different Levels in a Forest Canopy

Shoots from the lower levels of a Sitka forest canopy [Picea sitchensis (Bong.) Carr.] have much lower photosynthetic capacities per unit leaf area than do those from the top of the canopy. Chloroplast fragments have been isolated from the needles at three levels in the canopy and Photosystem I and Photosystem II activities measured. Measurements were made at eight photon flux densities giving light response curves for photosystem activity in the three canopy levels. Expressed per unit leaf area, light-saturated activities of Photosystem I and II were lower at the bottom of the canopy than at the top suggesting that photosystem activity might be limiting photosynthesis in the shoots from the bottom of the canopy. Chlorophyll concentration per unit fresh weight did not vary amongst the three levels, but specific leaf area increased and dry weight fraction decreased with increasing depth in the canopy, leading to a large reduction with depth in chlorophyll content per unit leaf area.