Loch Etive Research Articles

Laboratory study of predation by Aurelia aurita on larvae of cod, flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.

Comparison of laboratory rates of predation of five species of marine fish larvae by three planktonic invertebrates: effects of larval size on vulnerability

Rates of predation by the invertebrates Aurelia aurita, Thysanoessa raschi and Euchaeta norvegica on larval stages of cod (Gadus morhua L.), flunder (Platichthys flesus L.), plaice (Pleuronectes platessa L.), herring (Clupea harengus L.), and turbot (Scophthalmus maximus L.) were determined. Experiments were conducted in late winter and early spring 1982 with predators collected in Loch Etive, Scotland and prey obtained from several locations in Great Britain. Early stages of the smallest species, cod, flounder and turbot, tended to be most vulnerable to all three predators, while the early stages of the larger species, plaice and herring, and older stages of all species, were less vulnerable. For all stages and species of larvae, predation rates by the three predators were most closely related to larval length and escape swimming speed. Larval length itself was closely correlated to indices of larval escape ability. Low predation rates on large larvae by E. norvegica could be due to handling difficulties, whereas for A. aurita and T. raschi these low rates were due to escape abilities of the larger larvae. Prey movement is an important stimulus eliciting predation in E. norvegica but not in A. aurita or T. raschi.

A laboratory study of predation by Aurelia aurita on larval herring (Clupea harengus): Experimental observations compared with model predictions

Predation by the medusa Aurelia aurita L. on early first-feeding stage larvae of the herring clupea harengus L. was studied in the laboratory. The medusae were captured in Loch Etive, Scotland. Herring larvae were reared from the extificially fertilized eggs of spawning Clyde herring caught in March, 1982. Swimming speeds, volume searched”, capture efficiency and predation rates increased as medusa size increased. Predation rates on fish larvae increased with prey density, but appeared to approach a maximum at high prey densities; in 1 h experiments, a maximum rate of predation of 6.64 larvae h-1 was estimated by fitting an Ivlev function. A model to predict predation rates was constructed from swimming speeds, sizes and densities of medusae and larvae, and capture efficiency. The rates of predation predicted from the model fell within the range of experimental data, but tended to underestimate rates and did not account for saturation of medusae. Swimming patterns of medusae changed after prey capture: (a) before capture, encounter rates were low and medusae were relatively less active; (b) after capture of 1 larva, encounter rates doubled, with the stimulated medusae exhibiting increased activity and an aftered “searching” path; and (c) after capture of many larvae, swimming speeds and encounter rates of medusae decreased.

The breeding biology of Euchaeta norvegica (Boeck) (copepoda : Calanoida) in Loch Etive, Scotland: Assessment of breeding intensity in terms of seasonal cycles in the sex ratio, spermatophore attachment, and egg-sac production

The breeding biology of Euchaeta norvegicn (Boeck) has been studied in Loch Etive, Scotland, between 27 September 1971 and 24 August 1972. Information is presented on seasonal variations in the sex ratio of adults (stage VI), as well as stage IV and stage V copepodites, and examines the proportion of males present in the adult population as a factor determining the numbers of spermatophores attached to adult females and the quantity of egg sacs produced. These parameters are used to provide a measure of the intensity of mating, fertilization and breeding.

Some effects of salinity and temperature on the osmotic and ionic regulation ofPraunus flexuosus(Crustacea, Mysidacea) from Isefjord

Abstract The salinity tolerance, osmotic regulation and ionic regulation of the mysid crustacean, Praunus flexuosus, collected at the Isefjord, Denmark, has been investigated over a range of salinities, and at temperatures from 5 to 20 °c for both winter and summer animals. Survival at low salinities was enhanced when the animals were kept at low temperatures, and this enhancement was especially pronounced in animals collected in winter. A clear pattern of hyper/hypo-osmotic regulation was found, but no effect of season or temperature on the osmotic concentration was observed. The blood concentration of Isefjord animals was significantly lower at any given salinity than that of previously srudied animals from Loch Etive, Scotland. This reduction is considered to be due to long-term acclimation, and the findings are compared with other crustacea where studies have been made on distinct populations. The blood concentrations of sodium, potassium, calcium, magnesium and chloride were determined at three salin...

Parasites of marine sticklebacks

A total of three specimens of Spinachia spinachia and 11 Gasterosteus aculeatus were caught in Loch Etive, Scotland. The salinity of the water at the capture site was 23%. Nine species of parasites were collected from individuals of the mixed population of sticklebacks, which included seven new parasite records for the British Isles.

Soluble fractions of phosphorus compounds and alkaline phosphatase activity in loch creran and loch etive, Scotland

Reactive phosphorus, polyphosphate, monophosphate ester, dissolved organic phosphorus, and alkaline phosphatase activity were measured in Loch Creran and Loch Etive. Argyll, Scotland during the spring outburst of 1976. In addition, data on chlorophyll a, phacopigment, and salinity were obtained on each occasion. The mean levels of reactive phosphorus initially present in Loch Creran and Loch Etive were 0.50 and 0.22 μg-at. PO 4−P/I, respectively. As the diatom bloom progressed, it fell below the limit of detection. The mean values of polyphosphate were between 0.05–0.08 μg-at. PO 4−P/l in Loch Creran and 0.04 μg-at. PO 4−P/l in Loch Etive, and although present at the initiation and decline of the bloom, it was absent when chlorophyll a was high and the reactive phosphorus was low or undetectable. Monophosphate ester, was found in Loch Creran only, and then in the same concentration as that of the polyphosphate fraction. The mean levels of the dissolved organic phosphorus in Loch Creran and Loch Etive ranged between 0.08–0.18 μg-at. PO 4-P/l and 0.05–0.08 μg-at. PO 4−P/l, respectively. Alkaline phosphatase activity was detected when there was no reactive phosphorus in the water: the highest values in Loch Creran and Loch Etive were 0.003 and 0.005 I.U. of enzyme/4 ml of sample, respectively. The highest mean values of chlorophyll a were 8.0 μg/l in Loch Creran, and 6.0 μg/l in Loch Etive. The mean percentages of phaeopigment fluctuated between 20–55% in Loch Creran and 30–65% in Loch Etive. The highest values were found at the end of the bloom. The mean surface salinities ranged from 22.0 to 31.0‰ in Loch Creran and 3.7 to 17.0‰ in Loch Etive. The lowest values were recorded at the end of the bloom. The statistical treatment of the data, suggests a strong relationship between zooplankton grazing and levels of dissolved phosphorus compounds and phaeopigment.

Deep water renewal of Loch Etive: A three basin Scottish fjord

Loch Etive is a fjord with three basins. Innermost bottom water stagnates for months or years, with slowly changing temperature and salinity, falling deep oxygen concentration and with a secondary pycnocline below sill depth. A bottom water renewal is described and shown to be caused by low freshwater runoff. The renewal is a series of overflows of sill water during spring flood tides. During overflow, dense fluid forms a turbulent plume whose observed behaviour is similar to that expected from theory: an entrainment constant of 0.013 is found on a bottom slope of 6 °. Observations of salinity in the sill region show that the flushing time there is 4 weeks and that this is the response time of the renewal mechanism to changes in runoff. A model of the non-linear dependence of renewal upon runoff is made and used to hindcast during 1964–1975. The hindcast is verified and shows that renewal is aperiodic with a mean repetition time of 1 1 3 years.

Chemical investigations of Loch Etive, Scotland. I. Inorganic nutrients and pigments

For this work Loch Etive has been divided in three sections, namely, Lower Basin, Deep Basin, and Head of the Loch. The distribution and concentration of the inorganic nutrients are primarily the results of water movements and seasonal variations in biological activities. Phosphate is mainly supplied by the incoming water, but variable amounts of nitrate, silicate, ammonium, and nitrate are provided by run-off throughout the year. The surface (1 m) concentrations of phosphate, nitrate, silicate, ammonium, and nitrite during winter and late autumn, lay between 0.1-0.4 μg-at. PO 4-P/1, 3.0–7.0 μg-at. NO 3-N/1, 10.0–20.0 μg-at. SiO 4-Si/l, 0.10-0.80 μg-at. NH 4-N/1, and 0.01-0.16 μg-at. NO 2-N/1, respectively. During the dry period phosphate, nitrate, and silicate decreased gradually on proceeding from stations near the mouth to those at the Head of the Loch where they were barely detectable. During the wet periods of the summer months, nitrate and silicate exceeded the demands of the phytoplankton. The integral mean concentrations in the water column of the stations in the Lower Basin lay between 0.08-0.39 μg-at. PO 4-P/1, 0.6-6.7 μg-at. NO 3-N/1, and 2.8–11.0 μg-at. SiO 4-Si/l. In the Deep Basin, the integral mean values fluctuated between 0.46-0.80 μg-at. PO 4-P/1, 3.4–8.0 μg-at. NO 3-N/1, and 8.3–19.8 μg-at. SiO 4-Si/l. Except during the flushing period, nitrite and ammonium concentrations in this basin were very low. At the Head of the Loch the values ranged between 0.27-0.41 μg-at. PO 4-P/1, 2.23-5.80 μg-at. NO 3-N/1, and 7.0–11.8 μg-at. SiO 4-Si/l. The maximum of the spring outburst in 1970 was in the middle of March, while in 1971, a maximum (at 5 m) of 19 μg of chlorophyll a 1 was found somewhat later (26th March). The phytoplankton stock in the photic zone (as estimated by the chlorophyll a values) was not only dependent on the amount of nutrients, grazing, and light, but was largely determined by hydrographical factors which controlled its sinking. The concentrations of degraded pigment bore certain relationships to the levels of nutrient and light.

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. NO 3-N/l and 0.02-0.45 μg-at. PO 4-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).

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.

The relationship between maternal body size and clutch size, development time and egg mortality in Euchaeta norvegica (Copepoda: Calanoida) from Loch Etive, Scotland

Analyses of the relationship between the size and the number of eggs per female in various decapods, isopods, cumaceans and mysids were made by Jensen (1958) based upon personal research and information from available literature. Regression analyses indicated that the number of eggs per female is related to the cube of the body length.

The fish populations in inshore waters of the West Coast of Scotland. The distribution, abundance and growth of the whiting (Merlangius merlangus L.)

The whiting (Merlangius merlangus) is an important commercial species from the West Coast of Scotland. This paper describes the distribution, abundance, age composition and growth of juvenile whiting which are found in the inshore areas and sea lochs. No spawning was observed in the areas and it is assumed there was an active migration of whiting from the open sea. They were first caught by the bottom trawl in July, reached maximum abundance in November and December and thereafter declined in numbers until few remain by early summer. An exception to this occurs in Loch Etive and possible explanations for the fact that whiting tend to remain for longer periods and grow at a slower rate in this loch are discussed.

Sea trout in North Argyll sea lochs: II. diet

The diet of sea trout in some of the sea lochs of the west coast of Scotland was investigated. The contents of 986 sea trout stomachs from the Loch Etive area (1970–1973), and 291 stomachs from the Loch Eil area (1964–1973), were examined and the composition of the diet, seasonal changes and the effect of trout size were analysed using frequency of occurrence, dry weight and number of organisms methods. Benthic feeding (crustacea and annelids) was more important in winter while midwater and surface organisms (young fish and insects) were preferred in summer. Young fish (mainly clupeids and sand eels) featured more in the diet of larger trout (≤21 cm) than in the smaller size range (≥21 cm). Surveys of 24‐h were completed in June and September, 1972, and indicated that availability of food was the main factor influencing the presence or absence of trout. Bottom feeding was greatest during the day while the amount of midwater and surface feeding tended to increase between sunset and sunrise.

CONTROL OF FJORDIC DEEP WATER RENEWAL BY RUNOFF MODIFICATION / Réglage du renouvellement des eaux profondes des fjords en utilisant un modèle qui effectue une modification du régime de l'écoulement

Abstract Loch Etive is a Scottish fjord subject to fresh-water runoff which renders it markedly brackish. This paper considers the frequency of deep water renewal, developing a model which relates the timing of all such renewals to runoff records. Using the model one can examine the effect of changes caused by interference with the natural runoff pattern.

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive, Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 μm. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.

Palaeoenvironmental Interpretation of a Buried Soil at Achnacree, Argyll

The relationships between a humus iron podsol buried beneath a field bank at Achnacree, Argyll, western Scotland, and a normal sub-peat profile on an adjacent site are considered. It is suggested that the coarse-textured parent material and Ericaceous vegetational characteristics of the site induced and promoted progressive degradation of the profiles, which was possibly aided and enhanced by primitive cultivation practices. Translocation of humus is much more marked under the normal profile which reflects the operation of a more intensive pedogenic process which may be related, in turn, to the temporal factor in soil formation. Parallels are drawn with a site at Loughaveema, Co. Antrim, and it is suggested that soil deterioration was partially responsible for bog growth during the Sub-Boreal and Sub-Atlantic. THE Moss of Achnacree lies some 8 km north-east of Oban and covers about 312 ha of the southern part of the Benderloch peninsula at the entry to Loch Etive. The Moss, lying at an altitude of 65 m covers an extensive fluvio-glacial deposit derived mainly from Ben Cruachan granites and Loch Lorn schists. The deposit is considered by McCann (1961) to mark a halt in the retreat of a valley glacier which occupied Loch Etive. Since the late eighteenth century the edge of the Moss has been cut back, partly for fuel and in part to increase the area of arable land available to crofts located on the perimeter of the Moss. In 1968, a bank or field wall was discovered at G.R. NM 921349 overlying an old land sur- face. Both the bank and the surface had subsequently been buried by the growth of the Moss. Thus the bank and the surface beneath the bank clearly antedate parts of the peat which has built up to a depth of about 1-5 m. The bank is visible for some 60 m behind Croft 3 at Black Crofts, North Connell, before it disappears under the present peat face; it is about I-8 m wide and 0-4 m high and consists of two parallel lines of rounded granite and flatter schist stones with a central infill of rounded and sub-angular stones up to 8 mm in diameter within a gravelly loam matrix. This infill was thrown in from shallow ditches cut just outside the bank walls. About 5 cm from the surface of the infill bleached sand grains occur, showing the weak development of an A2 (Eb) horizon.

Surface nutrients, chlorophyll a and phaeopigment in some Scottish sea lochs

The distribution of several surface properties, both physical and chemical, of three Scottish sea lochs were studied during the spring phytoplankton bloom. Concentrations of nitrate, phosphate, and silicate have been determined and related to fluctuations in the freshwater input and uptake by the phytoplankton population. The ratios nitrate: phosphate and silicate: phosphate (on atom bases) in Loch Creran and Loch Linnhe were similar, but there were certain marked differences from those in Loch Etive. Nitrate, rather than phosphate, was a critical factor in the productivity of Loch Creran and Loch Linnhe. In Loch Etive the limitation of these nutrients was directly affected by the amount of fresh-water entering into the Loch. Patchiness of chlorophyll a and phaeopigments in Loch Creran and Loch Etive reflected those factors ( e.g., freshwater/sea-water inflow, turbulence produced by the loch topography etc.) which affect the surface circulation in the two lochs. The delay in the development of the phytoplankton bloom in Loch Linnhe may be attributed to a poor stability of the surface layers due to low run-off.

Nearshore zonation of benthic fauna, especially Nematoda, in Loch Etive

The marked pattern of vertical zonation in the nearshore distributions of benthic fauna in sea-lochs seems to be controlled by the degree of fluctuation and extent of depression in salinity (Gage, 1974). The different vertical patterns in the abundances of species can be related to their known tolerances to reduced and fluctuating salinity. An overall faunal discontinuity seems to occur at a depth which roughly corresponds to the maximum depth to which markedly brackish conditions are experienced.

The Loch Lomond Readvance and contemporaneous sea-levels in Loch Etive and neighbouring areas of western Scotland

During the Loch Lomond Readvance in western Scotland glaciers reached the seaward ends of Lochs Etive and Creran and extended to the head of Loch Feochan. On Mull the ice spread out from a mountain ice cap to terminate at the coastal zone. During deglaciation, outwash spreads were deposited in many valleys possibly during short stillstands due to topographic and/or climatic conditions. In Loch Etive, sloping series of well-developed kame terraces were formed and at Loch Creran there is evidence of a double moraine. Shortly after the culmination of the readvance, sea-level was below 12–14 m. O.D. at Lochs Etive and Creran and below 11–12 m. O.D. at Loch Feochan. Similarly on Mull the evidence suggests a sea-level, below 10–12 m. O.D. at this time, contrary to views expressed by previous writers.