W. J. P. Smyly's research while affiliated with Natural Environment Research Council and other places

1. The factors influencing the seasonal and inter-annual variations in the numbers of Daphnia hyalina in Esthwaite Water between 1956 and 1972 are analysed. Esthwaite Water has always been eutrophic. but the phosphorus and nitrogen loadings to the lake increased significantly in the mid 1960s. 2. Qualitatively, the phytoplankton and zooplankton populations in the lake changed relatively little during the period of study. Quantitatively, however, eutrophic species of algae became more abundant and the numbers of Eudiaptomus declined as the numbers of Daphnia increased. 3. The seasonal dynamics of the Daphnia was governed partly by the seasonal temperature cycle, and partly by the periodicity of edible algae. The birth rate of the Daphnia was constrained by temperature from January to April and from October to December. At other times their rate of increase was governed by the relative abundance of edible and inedible algae. 4. Edible and inedible species of algae tended 10 appear in a recurring annual sequence. Diatoms such as Asterionella were abundant in the spring, the early summer phytoplankton was dominated by edible flagellates, but inedible algae such as Aphanizomenon and Microcystis become dominant later in the year. 5. Daphnia could only reproduce in late summer when there were periodic regrowths of edible algae. Such regrowths were most likely to occur when there had been some entrainment of deep nutrients by episodic wind mixing. Calm weather encouraged the growth of blue-green algae that effectively‘blocked’the development of the Daphnia for the remainder of the summer. 6. The factors that controlled the seasonal dynamics of the Daphnia also influenced the average number recorded in a particular year. The average number of Daphnia increased in the early sixties when Cryptomonas was abundant and decreased in the late sixties when blooms of Aphanizomenon appeared in mid summer. Detailed analyses showed that a similar increase in the numbers of Aphanizometion had occurred in the late fifties. The critical factor throughout was the prolonged period of calm resulting in stable stratification. 7. This ‘weather’ effect was highlighted by comparing de-trended timeseries of Daphnia and Aphanizometion numbers with a simple measure of thermocline stability. De-trending removed the superimposed effects of progressive enrichment and revealed a 10-year cycle of thermocline stability that matched the temperature cycle recently reported in Windermere, These cycles are related to the movement of weather systems in the Atlantic so could change if the pattern of atmospheric circulation is altered by global warming. 8. The possible effects of climate change on Daphnia dynamics are discussed in relation to the findings in Esthwaite Water.

A survey is given of physical, chemical and biological events in the water-mass of a productive lake (Esthwaite Water, N. England) during summer stratification. They are interrelated in terms of i) responses to meteorological changes (ii) susceptibility to density stratification (iii) participation in acid-base and redox systems, with interactions of these (iv) modification due to the generation of particulate material from soluble precursors (v) limiting factors in such bio-generation (vi) mechanisms of internal nutrient loading, and (vii) control by the characteristics of individual plankters. The significance is demonstrated of differential inputs of meteorological variables, and especially of biological production and degradation, for determining the overall structure and metabolism of the lake.

Laboratory observations on the feeding of fourth instar larvae of Chaoborus flavicans (Meigen) show that features relating to the prey, such as swimming behaviour, size and shape, play a major role in determining the kind of food eaten by the predator. In tests with two interacting limnetic cyclopoid copepods, Cyclops abyssorum out-competed Mesocyclops leuckarti when Chaoborus was absent but did not do so when Chaoborus was present.

The population dynamics of Daphnia hyalina Leydig in a productive lake, Esthwaite Water, and an unproductive lake, Buttermere, in the English Lake District have been compared. The winter is passed as resting eggs in the bottom sediments in Buttermere and as free-swimming individuals in the planktonic zone in Esthwaite Water. In Esthwaite Water seasonal periodicity was characterised by maxima in spring and autumn and a minimum in summer; in Buttermere, there was no spring maximum and the first increase in population density was in summer. Population densities were higher and adult females were larger and laid more eggs per clutch in Esthwaite Water than in Buttermere. In each lake males became numerous in autumn. Observed rates of population increase, ‘r’ and calculated birth rates, ‘b’ and death rates ‘d’ were nearly always higher in Esthwaite Water than in Buttermere.

In a small lake (Blelham Tarn, English Lake District) two plastic cylinders, each of which extends from the lake surface to the bottom sediments and encloses 18 000 m3 of water, were used to investigate effects of enclosure on the zooplankton. This paper describes observations from March 1973 to October 1974 and is the second part of a report on a project spanning 4 years. Seasonal population densities of the more abundant species were essentially similar to those observed in the first part of the project, despite large changes in algal and predator populations. In the enclosures, fish (mostly Perca fluviatilis) populations are known from observations by divers to have been large in the period under consideration and small in the first part of the project. Populations of Chaoborus larvae in the enclosures were small at all seasons from March 1973 to October 1974.

The limnetic crustaceans of Grasmere, a small lake in the English Lake District, were studied from February 1969 to December 1970 (23 months) and from January to December 1975. These observations were made before and after a change in sewage effluent treatment effected in May 1971. Planktonic species, except for one cladoceran, were more abundant in the second than the first period, while hypolimnetic and profundal forms either became less abundant or modified their life-style in conjunction with a developing hypolimnetic oxygen-deficit.

Some morphological relationships during larval development of a freshwater cyclopoid copepod (Crustacea), Cyclops strenuus abyssorum Sars (Gurney, 1933) have been studied. The proportion which the cephalothorax forms of total length decreases at each copepodid moult whilst that which the furcal ramus forms increases. However, within each instar, each of these ratios is a constant at different seasons and in different lakes. The amount by which total length in one instar is greater than that in the preceding instar tends to decrease at each moult from a maximum of 1.31 in the first copepodid moult to lower values, especially in males. The furcal ramus is twice as long as wide in the first copepodid instar but seven times as long as wide in the adult female. This change is enhanced in the last two moults not only by a proportionately greater increase in length over width but by an absolute reduction in width itself.

1. Die Dauer der Eientwicklung ist bei 3 Süßwasser lebenden cyclopoiden Copepoden - Cyclops strenuus abyssorum Sars, Mesocyclops leuckarti (Claus) und Acanthocyclops viridis (Jurine)- untersucht worden, und zwar bei 4 konstanten Temperaturen. 2. Bei allen 3 Arten nimmt die Entwicklungsgeschwindigkeit mit zunehmender Temperatur zu. Der Kurvenverlauf entspricht Bělehrádeks Gleichung D = a (T-α)b, wobei D = Dauer der Eientwicklung, T = Temperatur, a, α, b = Konstanten. 3. Eier von M. leuckarti entwickeln sich bei Temperaturen über 9,5°C schneller als die von C. strenuus abyssorum, aber langsamer als diese unterhalb von 9,5°C. Über einen Temperaturbereich von 5° bis 16°C entwickeln sich Eier der benthonisch-litoralen A. viridis schneller als die der beiden planktonischen Arten. 4. Bei M. leuckarti variiert die Eistadiumdauer nur geringfügig als Funktion der geographischen Breite. Bei C. strenuus abyssorum war die Eistadiumdauer ähnlich in 3 von insgesamt 4 Englischen Seen; im vierten See (Buttermere) war die Eientwicklung signifikant langsamer bei 4° und 8°C als in den anderen 3 Seen; sie war jedoch nicht signifikant langsamer bei 12° und 16°C.

1. 1. In the freshwater cyclopoid copepod, Cyclops strenuus abyssorum Sars, yolk volume rarely exceeds about 20% of thoracic volume. This upper limit is nearly reached in all months of the year in Esthwaite Water, only in April and May in Rydal Water and Grasmere, and never in Buttermere, where the highest value was 8%.2. 2. In Esthwaite Water, thoracic volume is larger at all seasons than in the other three lakes investigated. Consequently, mean clutch size could never be as high in Rydal Water, Grasmere or Buttermere as in Esthwaite Water for this reason only.3. 3. Artificial feeding in the laboratory on nauplii of brine-shrimp nearly doubled mean clutch size of females from Rydal Water and Buttermere, and caused females in Buttermere to start breeding in October, although in the lake they do not do so until February or March.