Coldingham Loch, S.E. Scotland. II. Phytoplankton succession and ecology in the year prior to mixer installation

SUMMARY. 1. Total phytoplankton biomass in the small (8 ha), intermittently stratifying, eutrophic Coldingham Loch exhibited spring and autumn maxima of about 35 μg chlorophyll a l¹. Late winter and early spring assemblages included Chlorococcales (dominated by Coetxochloris pyrenoidosa Korsch. and Dichotomococcus curvatus Korsch.), diatoms (unicellular Centrales and Asterionella formosa Hass.) and desmids ( Closterium acutum Brèb. and Staurastrum chaetoceras (Schrod.) G. M. Smith). Small populations of Coetastrum and Oocystis characterized the summer period. The commonest "blue-green alga", Aphanizomenon flos-aquae Morr. ex Born, et Flah. (Cyanobacteria) attained its maximum population density in September just after the loch had permanently de-stratified. It was replaced by another growth of Closterium acutum which reached its annual peak density of 900 cells ml⁻¹ in October.
2. It is likely that nitrogen in summer and silica at various times of the year limited the growth of certain species; it is also possible that phosphorus limited growth in spring.
3. When physical conditions and nutrient concentrations are resolved into their basic, simple, seasonal patterns, a number of species preferences for particular environmental requirements become apparent. Of special significance is the competitive advantage over other plankters of Aphanizomenon in being able to resist sinking losses under stratified conditions and thrive at low ambient nitrate levels. Equally, there are some species exhibiting adaptability to a wide range of conditions.
4. The observed periodicity is examined in relation to recently published schemes that summarize phytoplankton-environment interactions.     

Phytoplankton ecology of Loch Ard,Scotland

The results of the ecological investigation discussed in this paper represent the first seasonal study of the phytoplankton to be carried out in Loch Ard. This body of water is a typical warm monomictic lake, with water temperatures during the period of study ranging from 18.6 to 4.4 °C and oxygen saturation from 68 to 112%. Stratification lasted from May to November. Phosphate was generally very low, being almost undetectable for about six months and not exceeding 0.125 µg.at.P 1^–1 even at the winter maximum. Dissolved silica showed a regular seasonal pattern ranging from 9 to 21 µg.at.Si 1^–1. Nitrate, like silicate, never showed signs of complete exhaustion, with a minimum of 4.0 and a maximum of 21.0 µg.at.N 1^–1. The pH remained on the acid side of neutrality while the alkalinity never exceeded 7 mg CaCO₃/1.From an examination of net phytoplankton Loch Ard could be described as diatom-desmid in nature. Quantitatively the population was dominated by diatoms(Cyclotella, Asterionella andMelosira) till May whence a mixed population of blue-green algae, desmids and dinoflagellates persisted till late September.     

Chemical investigations of Loch Etive,Scotland. II. Dissolved organic compounds

Variations in the levels of dissolved organic compounds in Loch Etive were studied during 1971. The amount of dissolved organic nitrogen, dissolved organic phosphorus, and Gelbstoff were markedly affected by the freshwater run-off. The surface (1 m) concentrations of the dissolved organic nitrogen and dissolved organic phosphorus throughout the year ranged from 3.0–9.0 μg-at. NO₃-N/l and 0.02-0.45 μg-at. PO₄-P/1, respectively. The surface levels of Gelbstoff during the year as measured by the optical density of the water at 320 nm and 400 nm fluctuated between 0.08-0.490 and 0.020-0.140, respectively. In the bottom layers of the Lower Basin (40–50 m) the optical density of the water at 320 nm and 400 nm throughout the year ranged between 0.060-0.150 and 0.010-0.047, in the Deep Basin (115–140 m) the values were between 0.086-0.130 and 0.018-0.037 and at the Head of the Loch, (25–35 m) they fluctuated between 0.080-0.229 and 0.017-0.052, respectively. The vertical concentrations of the dissolved organic nitrogen, dissolved organic phosphorus and Gelbstoff decreased irregularly from the surface downward. The concentrations of the dissolved organic nitrogen at the surface of the Lower Basin during the year were similar to those found at 40–50 m. In the Deep Basin and at the Head of the Loch the surface values were higher than those observed at 115–140 m and 25–35 m, respectively. The concentrations of the dissolved organic phosphorus at the surface of the Lower Basin were close to those found at the bottom (40–50 m). In the Deep Basin the surface values were higher than those at 115–140 m and at the Head of the Loch the surface concentrations were variably higher or lower than the bottom layers (25–35 m). The ratio of the optical density at 320 nm and 400 nm in the photic zone (1 m, 4–5 m, and 10 m) during the year ranged between 3.2–4.0 with the lowest ratios in winter and autumn. A similar pattern was observed in the water column of the Lower Basin and at the Head of the Loch. In the deeper strata of the Deep Basin, ratios were usually between 4.0–5.3 for most of the year. A comparison between the optical densities of the surface water during winter and autumn and that at 115–140 m (Deep Basin), suggests that the fraction more liable to precipitate is found in the visible region of the spectrum (400 nm).     

A hermaphroditic Arctic charr from Loch Rannoch, Scotland

An individual Arctic charr from Loch Rannoch was found to contain a gonad the anterior portion of which consisted of ovarian tissue. This is an extremely rare condition in salmonid fish and in this instance is possibly the result of environmental contamination.     

3. Fleck's Loch Bog (Foula,Shetland, Scotland,UK)

Different fractions of spores and sporangia of Acrostichum aureum were tested for allergenicity. Both the exine and protoplasm were active and allergenic material was present in both the spores and the sporangial matter.     

Trophic polymorphism amongst Arctic charr from Loch Rannoch, Scotland

This paper describes the results of a multivariate and univariate morphometric analysis of three groups of Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration (bright v. cryptic) and site of capture (from two locations 12 km apart). The analysis produced a clear and highly significant distinction, not only between brightly and cryptically coloured charr, but also between the two cryptically coloured groups, one of which was more robust in terms of several size-independent head measurements. Stomach analysis showed that the brightly coloured charr fed entirely on zooplankton, the less robust, cryptically coloured fish, fed on benthic macroinvertebrates, whereas a significant proportion of the diet of the more robust cryptically-coloured form consisted of other fish. Differences in length at age also distinguished the three forms, with the robust, piscivorous charr, which live longer and potentially reach a larger final size, attaining smaller sizes at a given age. These data clearly confirm the previous identification of a distinct planktivorous morph of Arctic charr in Loch Rannoch and extend the morph analysis by distinguishing two additional morphs, a benthivorous morph and a piscivorous morph that are morphologically and ecologically distinct. The results are discussed in the context of other systems in which sympatric morphs of Arctic charr have been described.     

Observations on a diatom bloom in Loch Leven, Scotland

A study was made on a freshwater planktonic population of centric diatoms, mainly Stephanodiscus rotula (Kütz.) Hendey, in Loch Leven, Kinross, Scotland. The observations were analyzed in relation to changes in water temperature and chemistry, parasitism by a chytridiaceous fungus, grazing by a recently described protozoan and competition from another alga ( Synechococcux sp.). Each of these factors is thought to have affected the recorded rise and fall in diatom population density, in particular, silica limitation, fungal parasitism and protozoan grazing.
The protozoan involved ( Asterocaelum algophilum Canter) forms digestion cysts, the predominantly diatomaceous contents of which suggested very selective feeding but laboratory experiments with dual cultures did not confirm this. They indicated that both the size and quality of algae affected their suitability as food. Feeding activities of Asterocaelum seemed to be more or less confined to a solid surface; grazing rates in cultures shaken to maintain the animals and algae in suspension were low relative to those observed in unshaken cultures. This suggests that much of the grazing occurred on diatoms that had sunk onto the sediments.     

A history of scientific research at Loch Leven,Kinross, Scotland

Loch Leven is a large, shallow lake in lowland Scotland, UK. Scientific research began here almost 200 years ago. Early research characterised the biodiversity and physical characteristics of the loch, providing an important historical background for future research. In the mid-1960s, this ad hoc approach was superseded by a more structured research programme under the umbrella of the International Biological Programme. This was the beginning of the Loch Leven long-term monitoring programme. Today, the results of these studies form one of the longest and most comprehensive limnological datasets for shallow freshwater lakes in the world, comprising more than 500 physical, chemical and biological variables collected at two-weekly intervals. To celebrate the 40th anniversary of the start of the long term monitoring programme, and to highlight the scientific investigations still being conducted at Loch Leven, the NERC Centre for Ecology & Hydrology (CEH) organised a symposium entitled “Loch Leven: 40 years of scientific research” in Kinross, Scotland, UK, on 11 December 2008. This examined the role of long-term monitoring in developing our understanding of the links between pollution, climate change and ecological responses in shallow lakes. This article introduces a series of papers summarising the scientific results presented at this meeting.     

The ecology of Synchaeta kitina Rousselet in Loch Leven,Scotland

Synchaeta kitina Rousselet reached population densities of up to 5000 ind.l^–1 in Loch Leven, between January 1977 and December 1982. The species was found over the entire range of temperatures recorded (0.4–21.4 °C), but was most abundant at temperatures above 7 °C. Embryo development times, determined under laboratory conditions, ranged from 122 h at 2 °C to 12.5 h at 20 °C. There was a marked inverse relationship between populations of S. kitina and Daphnia hyalina var. lacustris in the loch. It seems unlikely that this was due to interference competition from Daphnia. S. kitina can be cultured on Rhodomonas minuta var. lacustris and there is some evidence that this rotifer also feeds on small flagellates in its natural environment.     

Phytoplankton ecology of Loch Achray (Scotland)

Loch Achray is a warm monomictic lake in the Scottish highlands with water temperature ranging from 4 °C to 18.7 °C. The oxygen distribution is mainly clinograde with saturation values ranging from 76 to 112%. The general pattern of nutrient variation is irregular particularly for phosphate. Dissolved silica (measured as silicate) showed a range of 24 μg at. Si l⁻¹; phosphate varied from 0.24 to 0.03 μg at. P l⁻¹ while nitrate ranged from 3.5 to 15.2 μg at. N l⁻¹. The pH remained below 7 for the entire year and the alkalinity was very low, ranging from 2.5 to 6 mg CaCO₃ 1⁻¹. The examination of net samples showed Loch Achray to possess a poor phytoplankton population, consisting mainly of desmids and a few diatoms. The quantitative investigation showed a different picture of variation. There was no clear phytoplankton increase till May when a simultaneous increase occurred involving Melosira, Asterionella, Tabellaria fenestrata and Cyclotella. In July the population was dominated by Anabaena, while Cyclotella and Staurastrum became dominant in August.     

Rotifer occurrence in relation to water temperature in Loch Leven,Scotland

Many rotifer species in Loch Leven show a distinct seasonality in occurrence. This appears to be primarily an effect of temperature. While some species seem to be eurythermal, other species show a well-defined range of temperature preference, outside which they are unable to maintain populations. Within this range, there is a close correlation between food availability and rotifer abundance.     

Chemical investigations of Loch Etive,Scotland. III. Participate organic carbon and particulate organic nitrogen

The concentration of the suspended matter in Loch Etive varies with river discharge, biological production, and water movement. The contribution from phytoplankton production shows a seasonal trend, with the highest values in the spring and the lowest in winter. The carbon: chlorophyll a and nitrogen: chlorophyll a ratios in the photic zone (1,4–5, and 10 m) during the period of high production ranged from 54.0 to 400.0 and 6.0 to 38.0, respectively, the autumn bloom having higher ratios than the spring bloom. The increase of these ratios in the landward direction indicates the influence of terrestrial material. The C/N ratios in the surface (1 m) of the loch throughout the year fluctuated between 6.5–20.0, being the highest in winter. The C/N ratios in the bottom layers of the Lower Basin (40–50 m), Deep Basin (115–140 m) and the Head of the Loch (25–35 m) during the year ranged between 2.25–14.0, 5.0–38.0, and 3.0–28.5, respectively. The lowest ratios were mainly found in early autumn and associated with high levels of dissolved organic nitrogen and amonium. The accumulation of suspended matter in the deeper layers of the Deep Basin was caused by the input of organic detritus from the Lower Basin and eroded sediment from the basin slope. The lateral distribution of the C/N ratios may be related to the hydrographical features of the loch.     

Daily ration of adult perch, Perca fluviatilis L. during summer in Loch Leven, Scotland

Adult perch, Perca fluviatilis L., were sampled at 3-hourly intervals throughout 24-h periods from June-September 1971, and in June and August 1972. The wet weight of each major food component from the stomachs was expressed in parts per 10 000 of the fresh weight of the fish. From samples at capture, and others taken from caged fish at known time-intervals after capture, the rate of stomach evacuation was estimated. Food consumption between netting times was calculated as the increment between successive initial values of stomach contents, plus the amount evacuated in the interval. As the evacuation rate of caged fish was slower than that of free fish the estimates of food turnover are minimal ones. The perch were consuming 6.5 % of their wet body weight per day in June, and this ration had decreased to 3.2% by September.     

A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

On the ecology of notholca squamula muller in Loch Leven,Kinross, Scotland

Notholca squamula was rarely found in Loch Leven when the water temperature rose above 10°C. Under favourable temperature conditions its abundance appeared to be closely related to that of Asterionella formosa. In the laboratory the animal was seen to feed on this diatom by breaking open the frustule and ingesting the cell contents.Part of a dissertation for the Degree of Doctor of Philosophy to the Council for National Academic Awards at Paisley College, Scotland, in conjunction with the Institute of Terrestrial Ecology, Edinburgh, Scotland     

Tracking Atlantic salmon smolts, Salmo salar L., through Loch Voil, Scotland

Twenty-two salmon smolts, Salmo salar L., carrying miniature sonic tags were tracked individually for periods of up to 175 h in Loch Voil, Scotland, during May 1979 and 1980. Activity was predominantly nocturnal, 80% occurring between 21.00 and 06.00 hours, and was apparently undirected. Average velocities during this active interval were 0.6 body lengths per second (bl s⁻¹), with 98 and 93% of the time spent moving at less than 2 and less than 1 bl s⁻¹, respectively. The rates of downstream displacement were 0.04 bl s⁻¹ in 1979 and 0.01 bl s⁻¹ in 1980. The direction of displacement of smolts and of movement of water at a depth of 1 m was positively correlated ( P <0.001) and smolt displacement was biassed slightly ahead of water movement. Mean step lengths were 141 and 200 m in 1979 and 1980, respectively. Rates of downstream passage of 327 ICES plate-tagged smolts released 16.8 km upstream of the fish trap at Clunie dam, Loch Tummel, during the spring migrations of 1975 and 1976 averaged 0.13 bl s⁻¹ in each year: net surface water movement was about 3.7 times this rate during the same intervals. These data are consistent with the model of passive smolt migration postulated by Tytler et al. (1978) and suggest that the active component required to ensure passage through a loch (Thorpe & Morgan, 1978) is very small.     

Reproductive isolation and genetic differentiation of ferox trout from sympatric brown trout in Loch Awe and Loch Laggan, Scotland

Molecular marker studies reported here, involving allozymes, mitochondrial DNA and microsatellites, demonstrate that ferox brown trout Salmo trutta in Lochs Awe and Laggan, Scotland, are reproductively isolated and genetically distinct from co-occurring brown trout. Ferox were shown to spawn primarily, and possibly solely, in a single large river in each lake system making them particularly vulnerable to environmental changes. Although a low level of introgression seems to have occurred with sympatric brown trout, possibly as a result of human-induced habitat alterations and stocking, ferox trout in these two lakes meet the requirements for classification as a distinct biological, phylogenetic and morphological species. It is proposed that the scientific name Salmo ferox Jardine, 1835 , as already applied to Lough Melvin (Ireland) ferox, should be extended to Awe and Laggan ferox.     

Seasonal variation in size spectra of phytoplankton assemblages in Loch Leven,Scotland

Greatest axial dimensions (GALD) of phytoplankton cells, colonies and filaments etc, are used to describe the size structure of whole assemblages of species in the shallow eutrophic Loch Leven (S.E. Scotland). Two-weekly samples over the period 1979–1982 have been analysed to determine whether variation in size spectra show seasonal trends. Size frequency distributions are displayed using — for the first time in studies of phytoplankton assemblages — the graphical method based on rankits. The paper describes how individuals to be measured were chosen without bias towards any particular type. Seasonal variation in temperature and nutrient concentrations are discussed in relation to algal size structure.In spite of irregular shifts in species composition and abundance, phytoplankton assemblage size spectra (PASS) exhibit seasonal patterns. Early in the year, when temperatures are low and herbivorous zooplankton sparse, small algae ( 15 µm) predominate. The winter-early spring assemblages often exhibit a normal size frequency distribution. Later in the year larger algae occasionally become relatively more numerous, and skewed or polymodal frequency distributions are recorded. Increases in large algae are usually associated with Daphnia population maxima; the inter-relationship is clearly demonstrated in time-series plots of GALD isopleths and Daphnia numbers.The potential of the PASS method to further knowledge on ecological controls of phytoplankton is discussed. The investigator is compelled to include all species in a sample. The rankit-dimension graphs retain all the data, so the position of each algal measurement and its influence on the size distribution can be observed. This approach may help to identify size ranges of algae removed by a wide variety of grazing zooplankton.