Impact of 21st century climate change on the Baltic Sea fish community and fisheries

The Baltic Sea is a large brackish semienclosed sea whose species-poor fish community supports important commercial and recreational fisheries. Both the fish species and the fisheries are strongly affected by climate variations. These climatic effects and the underlying mechanisms are briefly reviewed. We then use recent regional – scale climate – ocean modelling results to consider how climate change during this century will affect the fish community of the Baltic and fisheries management. Expected climate changes in northern Europe will likely affect both the temperature and salinity of the Baltic, causing it to become warmer and fresher. As an estuarine ecosystem with large horizontal and vertical salinity gradients, biodiversity will be particularly sensitive to changes in salinity which can be expected as a consequence of altered precipitation patterns. Marine-tolerant species will be disadvantaged and their distributions will partially contract from the Baltic Sea; habitats of freshwater species will likely expand. Although some new species can be expected to immigrate because of an expected increase in sea temperature, only a few of these species will be able to successfully colonize the Baltic because of its low salinity. Fishing fleets which presently target marine species (e.g. cod, herring, sprat, plaice, sole) in the Baltic will likely have to relocate to more marine areas or switch to other species which tolerate decreasing salinities. Fishery management thresholds that trigger reductions in fishing quotas or fishery closures to conserve local populations (e.g. cod, salmon) will have to be reassessed as the ecological basis on which existing thresholds have been established changes, and new thresholds will have to be developed for immigrant species. The Baltic situation illustrates some of the uncertainties and complexities associated with forecasting how fish populations, communities and industries dependent on an estuarine ecosystem might respond to future climate change.     

The Oxidation of Malate by Isolated Turnip (Brassica napus L.) Mitochondria: I. ULTRASTRUCTURAL OBSERVATIONS AND THE PRODUCTS OF MALATE OXIDATION

Washed and purified turnip mitochondria oxidize malate withrespiratory control and ADP: O values approaching 3.0 and producepyruvate as the principal product. Oxaloacetate is also producedin significant amounts but is removed by an endogenous mechanism.Malate dehydrogenase appears to be important to the oxidationof malate but requires the removal of oxaloacetate. During malateoxidation the mitochondria undergo configurational changes similarto those observed in animal mitochondria. Both ‘rightside-out’ and ‘inside-out’ submitochondrialparticles have been prepared. Right side-out particles oxidizemalate in the same way as intact mitochondria, whereas the inside-outparticles have a biphasic oxidation, the first phase producingoxaloacetate and the second, NAD-requiring phase producing pyruvate.It is concluded that malate oxidation is a complex process usingseveral enzymes located in the matrix compartment with a minorcomponent possibly on the outer face of the inner membrane.     

The loss of submerged plants with eutrophication II. Relationships between fish and zooplankton in a set of experimental ponds, and conclusions

SUMMARY. 1. In 1982 and 1983 sets of experimental ponds were left with their submerged plant communities intact (plant ponds) or were cleared manually of them (cleared ponds). The ponds were all fertilized with ammonium nitrate and with variable amounts of phosphate. In 1982 fish were removed from the ponds. Zooplankton communities were dominated by large Cladocera with Daphnia prominent in the cleared ponds and Simocephalus in the plant ponds. There was no detectable effect of differential phosphorus additions on zooplankton communities or populations.
2. In 1983 zooplanktivorous fish (mainly roach) were stocked in the ponds. In the plant ponds the fish did not survive, probably through severe deoxygenation and the zooplankton community again included large-bodied Simocephalus. Fish survival was variable in the cleared ponds. Where fish stocks were absent or low (0.5–1 g m⁻²) a Daphnia- dominated community persisted; at intermediate fish stocks (18.1 g m⁻²) Eudiaptomus gracilis was predominant and where fish stock was high (22.8–29.1 g m⁻²) Bosmina longirostris , and cyclopoid copepods dominated the communities. Mean biomass of the zooplankton community declined with increase in fish stock to between 5.1 and 18.1 g m⁻² then increased.
3. On the basis of results from the experimental ponds and elsewhere, a new hypothesis is put forward to account for the switch from aquatic plant to phytoplankton dominance in eutrophicated shallow lakes. It envisages dominance by either group to be possible as alternative states over a wide range of high nutrient loadings. It suggests that each state is buffered against increased loading by mechanisms involving plant and algal physiology and zooplankton grazer populations. The nature of the buffers and the reasons by which one state may be switched to the other are, discussed.     

Darkness and the activity of diquat and paraquat on tomato, broad bean and sugar beet

A period of darkness after treatment increased the activity of diquat and paraquat on tomato, broad bean and sugar beet. The extent of the increase was dependent on the time of day (and year) of treatment, on the light quality and intensity before spraying and on the duration of the darkness. Damage from morning treatments, unlike those in the afternoon, increased rhythmically with increasing darkness. The rhythm showed a maximum about every 24 hr and continued through several days of darkness. The results underline not only the complexity of diquat and paraquat action but also the importance of strictly controlling experimental procedure when studying their mode of action.     

The influence of darkness on the uptake and movement of diquat and paraquat in tomatoes, sugar beet and potatoes

Uptake of diquat and paraquat was doubled and occasionally quadrupled when tomatoes were darkened after treatment. The increase was not directly related to the duration of darkness because, after a time, uptake decreased. Three possible explanations for this decrease are considered, namely: diquat exudation from the leaves, downward movement into the roots and the complexing of diquat in plant tissue. Evidence was against exudation from leaves and downward movement into the roots. Diquat activity also depends on its degree of movement in the plant but the possible influence of other factors is discussed when treatments are made in the afternoon or in the morning after a period of reduced light intensity. In a CO₂-free atmosphere, uptake and activity increased in light and were comparable to those in darkness. Uptake is therefore not impeded by phyto-toxic effects of diquat but possibly by the presence of a high concentration of solutes or by photosynthetic intermediates.     

The Oxidation of Malate by Isolated Turnip (Brassica napus L.) Mitochondria: II. THE MALATE-OXIDIZING ENZYMES, NUMBER AND LOCATION

The enzymes of malate oxidation in turnip mitochondria havebeen partially purified and some of their properties studied.Turnips contain a cytoplasmic malate dehydrogenase and two mito-chondrialmalate dehydrogenases. These are all distinct isoenzymes withdifferent immunblogical properties but similar molecular weights.The K_m for malate is relatively high (8.3 mM) in the mito-chondrialenzymes. One of the mitochondrial enzymes is located in thematrix while the other is membrane-bound but within the matrixcompartment. This latter enzyme, which retains its NAD and activitywhen submitochondrial particles are prepared, is responsiblefor the first phase of malate oxidation in submitochondrialparticles. Two malic enzymes were isolated: one, an NADP enzyme, is a minorcomponent and was not studied further; the other, immunologicallydistinct from the malate dehydrogenases, is probably locatedin the matrix compartment. The K_m for malate oxidation (1.4mM) is relatively low. This malic enzyme which apparently lacksOAA decarboxylase activity is NAD-specific but is unstable.The possibility of multiple malic enzymes is discussed. Themalic enzymes are responsible for the second NAD-requiring phaseof malate oxidation in submitochondrial particles.     

A new aero-aquatic hyphomycete from Papua New Guinea and Australia

An aero-aquatic hyphomycete with setose synnemata and scolecospores with a central isthmus is described.     

The Effects of Seed Number and Prior Fruit Dominance on the Pattern of Fruit Production in Cucurbits pepo (Zucchini Squash)

Many plants, especially of species with indeterminate reproduction,show first-fruit dominance, in which the presence of developingfruit reduces future fruit maturation by increasing the abortionof later (younger) fruit and by inhibiting subsequent flowerproduction. We examined the effects of seed number on first-fruitdominance by experimentally manipulating the number of pollengrains that were deposited onto stigmas of zucchini squash andthen monitoring flower production, fruit growth, and fruit maturation.Our findings show (1) that fruits containing more seeds growfaster and achieve greater size; (2) that the presence of 6–15-d-oldfruit significantly decreases the probability of female flowerproduction while significantly increasing the probability offruit abortion; (3) that the number of seeds in the prior developingfruit has a significant effect on the probability of flowerproduction and fruit abortion, and (4) that when seed numbervaries among the fruits on a vine the fruit with the fewestseeds are the most likely to abort. It is concluded that thestrength of dominance by a developing fruit depends on the numberof seeds it contains and that this also influences the resultof fruit to fruit competition. Fruit abortion, fruit growth, Cucurbita pepo, size of pollen load, seed number, zucchini, squash     

Block of Conduction in Partially Depolarized Cardiac Purkinje Fibres induced by an α-Adrenergic Agent

IF discrete areas of the ventricular conducting system are exposed to high concentrations of K⁺, conduction through these areas is slowed so much that the impulse may re-enter the normal part of the conducting system after the end of the refractory period, thereby evoking another excitation of the heart (refs. 1 and 2 and our unpublished work). This slow conduction results from a slow response that resembles the slow component of the cardiac action potential³ and the action potential of normal fibres of the atrioventricular node⁴. Adrenaline enhances the response of Purkinje fibres, depressed by exposure to high K⁺ concentration⁵ and we now report that an α-adrenergic agent, methoxamine, depresses the slow response at concentrations that do not affect the normal action potential. This finding is of interest because very few of the actions of adrenergic agents on the heart can be attributed to the stimulation of α-receptors⁶, because selective depression of the slow response is further evidence that it differs qualitatively from the response of normal fibres (our unpublished work) and because it suggests that α-adrenergic agents may be useful in the prevention of certain cardiac arrhythmias.