ln the euphausiid shrimp Euphausi.a pacffica, a member of the oceanic plankton, growth was as rapid as 0.048 mm/day in juveniles in the laboratory, more than twice as fast as that observed for oceanic populations (0.02 mnr/day) by other workers. Periods between molting, which occurs throughout the life span, varied between 3 and 8 days depending on the temperature but not on the anount of food eaten. Respiration accounted for the major portion of the assimilation of carbon (62-87/) and molting, growth, and reproduction accounted for the remainder. In mature animals, 9/o of. the assimilated carbon rvas released as the organic portion of the eggs. Itapidly growing animals incorporated as much as 30/o of the assimilated carbon, but calculations for an oceanic population gave 9/6 as the incorporation of organic carbon into tissue (excluding eggs and molts) over the life span of the animal. Assimilation of ingested carbon (digestion) appeared to be high, usually over 80/6, as judged from tracer experiments. In the laboratory, crustacean nauplii seemed to be a preferred food over unicellular algae but both were eaten when available; one alga was rejected. Nauplii must be smaller than 0.8 mm for many to be ingested by adult E. pocif,ca. Molting, which mainly occurred at night, depressed feeding.'I'he filtering rates for the animal on unicellular algae are sufficient for growth and metabolism if the carbon available to the animal in the sea is equivalent to that contributed by both detritus and phytoplankton standing crop in the area of the northeastern Pacific Ocean vi'here E. paci.Jica is found.
The gut of the purple sea urchin, Strongylocentrotus purpiiratus, reveals a mass of algae in various stages of decomposition. Algae contain relatively small amounts of nutrients which are readily handled by enzymes ordinarily present in animals, but they possess galactans, alginic acid, agar and possibly some cellulose, none of which are digested by man or most animals. The urchins in the course of evolution may have developed enzymes which have enabled them to use these materials, or, like many of the ungulate herbivores, they might harbor bacteria, or, like the termites, they might shelter protozoans which perform this role for them.The first study was therefore concerned with the role of the digestive enzymes present in the gut of the urchin. The second consisted of studies of the digestive action of the flora of the urchin gut. The third was concerned with the over-all nutritional economy of the sea urchin.
SUMMARYThe oxygen uptake of eggs and larvae of Norwegian herring from Bergen (mean unfertilized egg dry weight about 035 mg) and of Baltic herring from Kiel (mean unfertilized egg dry weight about 0·10 mg) was measured by a reference diver and a Warburg respirometer. Anaesthetized Kiel larvae had values of about 0·10μl./larva/h and Bergen larvae 0·25μl./larva/h. When expressed as Qo (μl./mg dry weight/h) the values became Kiel 2·3, Bergen 2·5.Oxygen uptake of embryos before hatching and of larvae, expressed as Qo, was most affected by activity, increasing in very active organisms by five to ten times the resting value of 1-2 μl./mg dry weight/h. Experiments to test the effects of temperature and salinity were done using anaesthetized larvae in some cases.Temperature experiments with larvae gave a Q10 of about 2, the Qo, of anaesthetized Kiel larvae ranging from about 2·0 at 50° C to 35 at 14°C, and that of unanaesthetized Bergen larvae from 2·5 at 6° C to 50 at 140°C.Eggs and larvae of both races reared in salinities from 5 to 50 %0 showed no detectable difference in oxygen uptake. However, abrupt transfer of anaesthetized larvae from one salinity to another caused violent fluctuations (by up to ten times) before adaptation took place. Buoyancy differences appeared to mask differences in oxygen uptake of unanaesthetized larvae in similar transfer experiments.There was little tendency for oxygen uptake to become reduced during darkness in either Bergen or Kiel larvae.The effect of age on oxygen uptake (expressed as Qo) was not marked, though there tended to be a peak at, and just after, hatching, with a tendency for a fall off during starvation.
This review paper explores a number of hypotheses on the control of clupeoid populations. The following are discussed: the effect of fishing; egg mortality (predation); larval mortality (the critical period) with a consideration of starvation and predation and the biotic and abiotic factors that may be involved; larval transport and the oceanographic features that cause it; variable egg production; interspecific competition; and the effect of localized (e.g. storms and upwellings) and widespread (El Niño) oceanographic events. A review of the paleosedimentary record is also given showing the magnitude of natural fluctuations when no fishing occurred. Recent resurgences in clupeoid populations are reviewed and suggested causes are analyzed.
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