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.     

Coidingham Loch, S.E. Scotland

SUMMARY. 1. Coidingham Loch (Berwickshire. Scotland) (area. 8.4 ha, mean depth 2.9 m, max. depth 12.3 m) belongs to Hakansson's convex shape category. It lies in a basin of Silurian Greywackes rock within 0.25 km of coastal sea cliffs (c. 133 m a.s.l.). The theoretical hydraulic replacement time is 3.17 years. 2. The loch stratifies intermittently in summer. Fluctuations in oxygen concentration generally correspond to spells of mixing and stratification; low values of 10% saturation occur at the bottom. 3. The sum of the concentrations of major cations (Na+, K+, Ca²⁺, Mg²⁺) is in accordance with measured conductivities ranging between 380 μS cm^?1 and 420 μS cm^?1 (k.₂₅). The ratios (by equivalents) of Na⁺/Cl^? (0.04) are similar to those in sea-water, whilst values for Ca+²⁺/Cl^? (0.85–1.01) and Mg²⁺/Cl^? (0.79–0.88) reflect the bedrock. 4. Nitrate concentrations were lowest (<0.05 mg N1^?1) in summer following losses from the column of 107 mg N m^?2 1^?1, a rate corresponding well with published figures on microbial nitrate reduction. Nitrate increased at a rate of 8μg N I^?1 d^?1 to a winter maximum of 1.55 mg N I^?1. Mass balance calculations show that if this rise is attributed to run-off from surrounding land, a loss rate of 11.1 kg N ha^?1 yr^?1 would be required; this value is also commensurate with published figures. 5. Changes in phosphorus and factors controlling them contrast markedly with those of nitrate. The minimum concentration of 55 μg total P l^?1 (mainly in soluble reactive form) occurs in spring. An increase to the maximum ofc. 300 μg l^?1 in summer is sustained mainly by release from the sediments at a regular rate of 3 μg P l^?1 d^?1 (8.7 mg m^?2 d^?1). Adsorption by the sediments is considered to be the major process accounting for autumnal losses of phosphorus of 2.6 mg P M^?2d^?1. 6. Silica showed a less regular seasonal pattern, but varied some 45-fold with a maximum of 2.25 mg SiO₂, l_?1 in August.     

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 the Lake of Menteith,Scotland

The results discussed in this paper represent the first seasonal ecological study carried out on the phytoplankton of the Lake of Menteith. All measured nutrients reached maximum levels during the winter, with silicate showing particularly high concentrations (up to 85 µg at Si l^–1). During the summer period phosphate, nitrate and silicate showed almost complete exhaustion in surface waters. The lake water was consistently alkaline, never falling below pH 7, while the alkalinity ranged from 20 to 24 mg CaCO₃ l^–1. Generally, the nutrient status of the main inflow had a rapid effect on the water quality of the lake.The region of the lake under investigation showed no thermal stratification at any period of the year, although continuous thermal gradients were recorded in the winter. The continual circulation of the water mass probably prevented oxygen saturation from falling below 77% even following a large phytoplankton bloom and subsequent decomposition.From an examination of net phytoplankton samples the Lake of Menteith could be described as blue-green or blue-green/diatom in nature. From the quantitative study, large pulses of Melosira, Asterionella and Fragilaria were recorded in the spring. The disappearance of the species appears to be related to silicate limitation. The summer growth of Asterionella may have been promoted by a nitrogen source other than nitrate and nitrite, both of which were reduced to critical levels. This alternative source of combined nitrogen may have been contributed by nitrogen-fixing algae in the lake. Three species of Anabaena were recorded, all of which produced large populations during the year.Department of Botany, The University of GlasgowPresent Address: Department of Biology, College of Science, University of Sulaimaniyah, Sulaimaniyah, Iraq     

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     

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).     

Phytoplankton ecology in the Southern Benguela current. II. Carbon assimilation patterns

The patterns of carbon assimilation into the major end-products of phytoplankton photosynthesis were studied in the Southern Benguela current during the summer of 1979–1980 using [ ¹⁴C]bicarbonate as a tracer. Greater activity was measured in the polysaccharide (TCA-soluble) fraction in aged upwelled water (Type 3) than in maturing upwelled water (Type 2) at both high and low light intensities. Conversely, a greater proportion of the label was incorporated into the protein (TCA-insoluble) fraction in maturing than in aged upwelled water. An approximately equal distribution of the label between polysaccharide and protein at the 50% light intensity was recorded in freshly upwelled water (Type 1), but at the 1% intensity greater activity was detected in the ethanol-soluble fraction. In ageing upwelled water (Types 2 and 3) more carbon-14 was incorporated into polysaccharide at the 50% light intensity than at the 1% intensity, but the percent incorporation was greater in Type 3 water when low nitrate concentrations prevailed. In this ageing water radioactivity in the protein fraction was greater at the 1% intensity than at 50% intensity.     

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.     

Phytoplankton ecology in an unusually stable environment (Montezuma Well,Arizona, U.S.A.)

Relatively minor annual amplitudes of change in certain major nutrients, and especially pH and water temperature were measured in the spring-fed system of Montezuma Well, Arizona during a four year study. phytoplankton diversity was low but for the most part, composition was spatially and temporally constant; total seasonal phytoplankton density was significantly correlated with regional incident light. Phytoplankton species composition changed briefly during and for a short period following the summer monsoon. Ultraplankton (<5 µm diam.) numerically comprised nearly 80% of the phytoplankton community throughout most of the year. The limited residence time of water in the Well may have provided a competitive advantage for cells with high surface area:volume ratios and correspondingly rapid division rates. Nannochloris bacillaris Naum. and Coccomyxa minor Skuja were perennial dominants. Diatom populations did not increase with annual increases in vernal solar radiation. Low pH, high dissolved CO₂, and limited residence time for metabolic inhibitors are considered to be largely responsible for the reduced blue-green populations in the Well. The only flagellated photosynthetic group present in Montezuma Well was the Cryptophyta. Desmid populations were minimal, even though pH was consistently below circumneutral (6.5) and free CO₂ concentrations high. The role of grazing by an amphipod, Hyalella montezuma, on annual phytoplankton abundance is examined.     

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 changes in phytoplankton community structure in relation to physico-chemical factors in Loch Lomond,Scotland

Surface waters, sediments and the polychaete Nereis diversicolor were sampled in the ScheldtEstuary between 1990 and 1994. In surface watersparticulate Hg (Hg_P) concentrations ranged from350–1610 ng g^-1. They are essentiallycontrolled by physical mixing of polluted fluvialparticulates with relatively unpolluted marineparticulates, but unaffected by seasonal changes.Dissolved Hg species, on the other hand, show largeseasonal variations essentially controlled by theredox conditions in the estuary, as well as bybacterial and phytoplankton activity. Total dissolvedHg (Hg_TD) concentrations ranged from 0.5 to 3.0 ngl^-1 with 10 to 90% as reactive Hg. Highconcentrations of Hg_TD are found in the upperestuary in the winter and decrease rapidly withincreasing salinity. In summer Hg_TDconcentrations are low in the anoxic upper estuary andincrease as oxygen is restored in the estuary.Significant variations were observed in dissolvedMonomethyl Hg (MMHg) concentrations withconcentrations ranging from 0.01 to 0.120 ng l^-1 in the winter and 0.08 to 0.6 ng l^-1 in summerand autumn. Particulate MMHg ranged from 2 to 6 ngg^-1 in winter and from 4 to 10 ng g^-1 insummer and accounted for 20 to 80% of the total MMHg.Hg° concentrations ranged from 0.02 to 0.130 ngl^-1 and are higher in summer than in winter. Inthe lower estuary a positive correlation betweenHg° and phytoplankton pigments was observed. Sediments and the polychaete N. diversicolorwere sampled on the intertidal flat GrootBuitenschoor. Hg_{_T} concentrations in surfacesediments ranged from 144 to 1890 ng g^-1 and MMHgfrom 0.8 to 6 ng g^-1 accounting for 0.4 to 0.8%of the total mercury present. Both total Hg (Hg_T)and MMHg concentrations increased with increasedorganic matter content and anoxic conditions. On theother hand, accumulation of Hg_T and MMHg washigher in N. diversicolor living in coarse grainsandy sediments than in muddy sediments. MMHgconcentrations in N. diversicolor ranged from2.2 to 20.9 ng g^-1 accounting for an average of18% of the Hg_T. Seasonal variationssignificantly affected Hg speciation in sediments andN. diversicolor. Higher Hg_T concentrationswere found in the sediments in autumn and winter,whereas MMHg concentrations increased in spring andsummer. Likewise, higher MMHg concentrations were alsoobserved in N. diversicolor in spring andsummer. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

The feeding biology of the immigrant triclad Phagocata woodworthi in Loch Ness, Scotland

Laboratory feeding experiments and a serological examination of the gut contents of field-collected triclads indicated that Phagocata woodworthi Hyman feeds heavily on oligochaetes. Its realized food niche also includes Asellus , caddisflies, molluscs, chironomids, stoneflies and mayflies. It is concluded that Ph. woodworthi is a considerable threat to the British triclad fauna, because of the considerable overlap in diet with native species, its fast reaction time to damaged prey, and its polypharyngeal state.     

Dicranum spadiceum J.E.Zetterst. in Scotland,new to the British Isles

Abstract

Glenmassan, Dunoon, Argyll, UK     

Phytoplankton ecology in the Southern Benguela current. I. Biochemical composition

Investigations on phytoplankton communities in a nearshore region off the Cape Peninsula revealed three types of upwelled water. During active upwelling temperatures were < 10 °C and concentrations of inorganic nutrients were high (Type 1). Maturing upwelled water was characterized by temperatures > 10°C and nitrate concentrations varying between 2 and 15 μg-at. NO₃-N · 1^?1 (Type 2), while aged upwelled water (Type 3) contained low concentrations of nitrate (<2 μg-at. NO₃-N · 1^?1) at temperatures > 10°C. During the summer of 1978–1979 diatoms dominated the communities from October to January but microflagellates were dominant in February and March. In both types of community, low concentrations of ATP, chlorophyll a, protein and carbohydrate were measured in Type 1 water with protein/carbohydrate ratios being > 1. In Type 2 water concentrations of chlorophyll a, ATP and protein were high and the protein/carbohydrate ratio was > 1. Concentrations of chlorophyll a and ATP remained high in Type 3 water but the protein/carbohydrate ratio decreased to < 1 due to an increase in the concentration of acid-soluble glucan. It was concluded that the communities were in an active phase of growth in Type 1 and Type 2 water when adequate nutrients were available, but were in a slow-growing phase in Type 3 water when nitrate concentrations were low. Correlation coefficients, simple linear regressions and stepwise multiple regressions between biochemical and environmental variables confirmed that nitrate was the nutrient most closely related to the biochemical composition of phytoplankton. Using linear regression equations of biochemical variables on glucan it was estimated that chlorophyll a existed in a ratio of ≈ 1: 1 between living phytoplankton and bacteria/detritus, while the percentage of ATP was high in the phytoplankton component of Type 1 water but low in that of Type 2 water. The percentage of protein in detritus was greater than in living phytoplankton, and the carbohydrate content of living phytoplankton increased as the upwelled water matured from Type 1 and Type 2 to Type 3.