Margaret's Bay Research Articles

Analysis of the importance of spatial and temporal heterogeneity in the estimation of annual production by phytoplankton in a small, enriched, marine basin

In the Bedford Basin, Nova Scotia — a small, enriched, marine inlet — the annual production of phytoplankton was 220 g Cm −2yr −1 with a standard deviation of ± 35 gC m −2 yr −1. The relative contributions of spatial and temporal fluctuations to the variance of the estimate of annual production are assessed, and conclusions are drawn on the design of sampling programs. Although on any given day differences were observed in production rate among four stations, the estimates of annual production agreed within 5 %. The results from Bedford Basin are compared with those from neighbouring St Margaret's Bay, which is relatively unenriched.

Analyses of temporal variation in the structure of a shallow‐water benthic community in nova scotia

AbstractThe dominance structure of a shallow water (17 m), soft‐bottom community at St. Margaret's Bay, Nova Scotia was studied using multivariate statistical methods over the period January 1970 to January 1971. Seventy‐four species were encountered in the samples, and the majority were crustaceans and polychaetes. Ordination was the best method, compared to classification and measures of species diversity, for determining the changes in dominance from the mass of complex data. An ostracod (Normanicythere leioderma), two polychaetes (Micronephytis minuta and Prionospio steenstrupi), and an amphipod (Photis reinhardi) were identified as the species that determined change in the assemblages resulting from the multivariate analyses. The changes in these species' population structure were related to seasonal fluctuations in temperature.

Seasonal Changes in Feeding and Particle Selection by Winter Flounder (Pseudopleuronectes americanus)

Abstract The mean weight of food items from winter flounder (Pseudopleuronectes americanus) at St. Margaret's Bay, Nova Scotia closely coincided with the mean weight of benthic prey potentially available. Flounder larger than the mean length (29 cm) ate heavier particles. Small particles were consistently disregarded. There were seasonal changes in the weights of food items used and in the proportion of organisms to detritus in stomachs.

Systems Engineering Aspects of the Proposed Channel Navigation Information Service

This paper, by the head and the deputy head of the Civil Marine Navigational Aids Division of the Admiralty Surface Weapons Establishment, deals with certain problems relating to the proposed Channel Navigation Information Service, including radar coverage, the transmission of information, computer assistance and information display. The paper was read at a meeting of the Institute held in London on 30 January 1974 with the President in the Chair.Much of the background to marine traffic problems in the Dover Strait has already been discussed in previous issues of this Journal. It was decided in 1971 that some radar surveillance of the area would be appropriate. The first steps were taken when a radar trial was conducted by A.S.W.E. in the St. Margaret's Bay area near Dover in 1971. As a result of these trials the Coastguard station at St. Margaret's was fitted with a standard marine radar as an interim solution.

The Phytoplankton of St. Margaret's Bay

The Phytoplankton of St. Margaret's Bay

Metabolism and its relationship with growth rate of American plaice, Hippoglossoides platessoides Fabr.

Low routine oxygen consumption rates were measured for 100 American plaice ( Hippoglossoides platessoides Fabr.) which were taken from St. Margaret's Bay, Nova Scotia, on five occasions (August, November, February, April and June) during 1970–1971. The pooled data for the rate of oxygen consumption R(mg O 2/h) at weight w(g) are represented by the equation R = 0.0582 w 0.8. Over the range 1–6 °C no significant ( P < 0.05) effect of temperature on oxygen consumption was detected. Neither season, sex, state of maturity, nor stage of gonad ripeness had significant effects upon the rate of oxygen consumption. A comparison of the data with those for other species of flatfish gives no evidence for an evolutionary adaptation of metabolic rate to the prevailing subarctic temperatures. An analysis using a growth equation derived from energy principles indicates that the influence of temperature on metabolic rate can account for the differences in growth rate among plaice populations but that characteristics of the food supply may also have an important effect.

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. III. Energy transformations by sea urchins

An energy budget was constructed for a population of the sea urchin Strongylocentrotus droebachiensis in the nearshore area of St. Margaret's Bay, Nova Scotia, Canada. Of the 6 age classes identified, ages 1+and 2+accounted for about 1/2 the population energy flow. Population production efficiencies were: production/assimilation=0.28, production/consumption=0.04 to 0.13, and production/biomass=0.80. Although S. droebachiensis was the dominant herbivore in the seaweed bed, it utilized only 1 to 7% of seaweed production. As with other populations of sea urchins, however, it had a proportionately greater influence on seaweed biomass, and also presumably production, by clearing seaweed from large areas of substrate and maintaining it clear. Loss of dissolved organic matter, the only term in the energy budget not measured, was estimated by substracting the other terms in the energy budget from consumption. In laboratory individuals, this ranged from 40 to 80% of absorption (consumption-faeces). A critical review of energy budgets for 6 other species of marine benthic grazers also revealed large amounts of energy unaccounted for that might be attributed to loss of dissolved organic matter.

Summer Storage of Energy and Its Use for Winter Metabolism and Gonad Maturation in American Plaice (Hippoglossoides platessoides)

American plaice (Hippoglossoides platessoides) in St. Margaret's Bay, Nova Scotia, had an annual energy storage cycle in which a mature 35 cm female stored 92 kcal during the summer period and used this energy for metabolism (72 kcal) and gonad maturation (20 kcal) in winter months. An additional 21 kcal was stored in the ovary during the summer period. These energy changes occurred in a fish with a total energy content of approximately 300 kcal and an annual energy increment of 51 kcal due to growth in length. The annual energy variation in immature females and males was less than in mature females. A comparison of summer production (143 kcal, excluding gonad energy) with net annual production (51 kcal) for a 35 cm female plaice indicated that higher yields would be obtained by harvesting at the end of the summer period than by taking the same fish at the end of the overwintering period.

Yearly Respiration Rate and Estimated Energy Budget for Sagitta elegans

The respiration rate of Sagitta elegans in Bedford Basin, Nova Scotia, was found to be significantly different at different times of the year. Respiration rates were lower in summer and fall than during spring because the animals acclimated to warmer temperatures as the year progressed. The annual energy expenditure by respiration of the S. elegans population in St. Margaret's Bay, Nova Scotia, was equal to the net yearly production of the population; the calculated minimum ingested energy for this population was estimated to be between 13.2 and 20.0 kcal 100−3 year−1, or about 0.7–1.1% of the estimated total energy produced annually by copepods in the Bay. S. elegans probably has its greatest impact on the zooplankton community in St. Margaret's Bay during winter and early spring, when its biomass is greatest and its energy of respiration per unit volume of water is highest.

Ecological energetics of the sea-weed zone in a marine bay on the Atlantic coast of Canada. II. Productivity of the seaweeds

The growth of the seaweeds Laminaria longicruris, L. digitata and Agarum cribrosum were followed by SCUBA divers for two years, by punching holes 10 cm from the junction of stipe and blade, and recording at intervals the distance the holes had moved. As the holes approached the tip of the blade, new holes were punched at the base. It was found that the blades behaved like moving belts of tissue, eroding at the tips while growing at the bases, so that a total year's growth amounted to 1 to 5 times the initial length. Larger, older plants had wider and thicker blades, and the biomassincrease was roughly proportional to the square of the lengthincrease. Growth was most rapid in January to April, slow in July to October. As a conservative estimate, the summer biomass of the various species of seaweeds had a turnover of 4 to 10 times in the course of 1 year. Applying these figures to an earlier survey of biomass, it is estimated that annual production of seaweeds in St. Margaret's Bay, Nova Scotia, Canada, amounts to 603 gC/m2 averaged over the whole bay, 1750 gC/m2 averaged over the sea-weed zone, or 648.000 gC/m of shore line. Approximate calorific equivalents are 6030 kcal/m2 over the whole bay, or 6480×103 kcal/m of shore line.

Distribution of Herring (Clupea harengus) Larvae Along the Southern Coast of Nova Scotia with Observations on Their Growth and Condition Factor

The distribution and abundance of herring larvae on the southern coast of Nova Scotia suggested the presence of a fall spawning population. Larvae were found in St. Margaret's Bay from late September to June. They showed a slower growth rate than larvae from the Clyde Sea, Scotland, and weighed less at a particular length than did larvae from the Clyde Sea and Boothbay, Maine. The larvae had a lower condition factor at 25 mm length than larvae from the North and Baltic Seas. No larvae were found on the Scotian Shelf during late May and early June, 1969, but were abundant during September and October. Herring spawning beds were reported from areas along the entire coast of Nova Scotia from Canso to Cape Sable.

Some Relations of Land Drainage, Nutrients, Particulate Material, and Fish Catch in Two Eastern Canadian Bays

A year's record of the carbon content of living and of carbon and nitrogen content of nonliving suspended particulate material from St. Margaret's Bay, Nova Scotia, is presented. From considerations of carbon/nitrogen ratios and nutrient data from other sources, the nitrogen budget is briefly considered. The possible importance of land drainage into the bay leads to some positive correlations between runoff and catch of four commercially important species in the Gulf of St. Lawrence.

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. I. Zonation and biomass of seaweeds

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x103 kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m2 fresh weight, 0.30 kg/m2 dry weight, 91 g/m2 carbon or 912 kcal/m2. Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.

Production Potential of a Seaweed–Lobster Community in Eastern Canada

An energy-flow diagram for the bottom community in the seaweed zone of St. Margaret's Bay, Nova Scotia, has been constructed, using previous estimates of seaweed production and observations on animal biomass and respiration rates. Annual seaweed production exceeded the annual consumption by herbivores by a factor of more than 10 (7000 vs. 572 kcal/m2 per year). This fact, plus observations of physical processes in the seaweed zone, indicate that most of the seaweed production is exported as particulate matter in suspension. Production rates of the American lobster (Homarus americanus) prey species exceed lobster ingestion rates, also by a factor of more than 10 (84 vs. 6 kcal/m2 per year). The difference is presumably consumed by lobster competitors. The available information suggests lobster production in the seaweed zone could be increased by reducing predation and competition for food, together with an increase in suitable shelter.

The overall change in abundance of ciliates other than Family Tintinnidae in St. Margaret's Bay

The overall change in abundance of ciliates in St. Margaret's Bay is described. Oligotrichida other than Tintinnidae were the dominant group. Maximum concentrations of ciliates occured in June and July when microflagellates were also abundant.[/p]

Life History, Ecological Production, and an Empirical Mathematical Model of the Population of Sagitta elegans in St. Margaret's Bay, Nova Scotia

The population of Sagitta elegans Verrill in St. Margaret's Bay, Nova Scotia, was polymodal throughout the year. The modes were distinct enough to be considered as representing subpopulations. Four subpopulations were present in the Bay during the early winter and a fifth subpopulation entered the Bay during the late winter. The growth of the subpopulations was followed through the year and related to the mean water temperature. A mathematical model describing the effect of temperature on development, length of the life cycle, and reproductive potential is presented. The model simulates the effects of temperature on the body length at maturation, ovary length, generation time, and numbers surviving at various body lengths. Predictions are made on the changes in population size due to temperature, and mortality and flushing rate changes. The calorific content of the animals at different stages of the life history are given along with the carbon content of the animals. A yearly ecological production figure is given based on the turnover rates derived from the Allen curve for one of the subpopulations. The significance of the findings is discussed in relation to the geographic distribution of the species.

The Annual Production by Phytoplankton in St. Margaret's Bay, Nova Scotia

The Annual Production by Phytoplankton in St. Margaret's Bay, Nova Scotia

Relation between Biomass, Productivity, and Loss to Predators in a Population of a Marine Benthic Polychaete, Pectinaria hyperborea

The changes in population density and individual size distribution in a population of the trumpet worm Pectinaria hyperborea Malmgren were observed on eight occasions in 20 months at a station 60 m deep on a soft muddy substrate in St. Margaret's Bay, N.S. Production proceeded rapidly during the early life stages while loss due to mortality (elimination) was low, so that biomass increased and reached a maximum at 170 days. Between 30 and 370 days the rate of elimination was nearly constant at about 0.9 g/m2 wet weight per 50-day period in spite of changing biomass. After 370 days the rate of production, rate of elimination, and biomass decreased. It was estimated that 80% of mortality was due to predation. Almost 90% of total production of the cohort took place in the first year of life. The ratio between annual production and biomass present in May 1967 in the study area was used to estimate annual production at 24 stations in the bay.

Spatial Heterogeneity of Phytoplankton in a Near-Shore Environment

An analysis of variance model for phytoplankton distribution is described, which allows the partition of the variance of chlorophyll observations into effects due to differences between stations, to differences between replicate samples at the same station, and to handling and analytical error. When the model was applied to observations of chlorophyll made in St. Margaret's Bay, N.S., it was found that, on the average, the variance between replicate samples on the same station was of the same magnitude as the analytical error variance. Significant differences were revealed between stations even at densities as high as 10 stations per 0.0625 sq miles. As the sampling area was increased (but the number of stations kept constant), the between-station variance rose rapidly, to a density of 10 stations per sq mile, after which it remained relatively constant. The maximum value of the between-station component of the variance was about 10 times the average for the between-replicate component. Heterogeneity of plankton distribution gave rise to coefficients of variation (logarithmic) up to 70% for single observations of chlorophyll concentration, for which the analytical technique has a precision of better than 10%.Analysis of chlorophyll samples taken at closely spaced stations (0.1 miles apart) along an 8-mile transect revealed considerable variability in distribution. Autocorrelation analysis of the data showed the presence of plankton patches 0.5–1.5 miles in diameter. Coherence analysis provided some evidence for correlation between the distribution of chlorophyll and of temperature and salinity. The dominant frequency in coherence spectra was −3 cycles/mile. Comparison of the autocorrelation function for chlorophyll with those for temperature and salinity indicated the influence of both deterministic and random processes on the chlorophyll distribution.Measurements taken at nine stations during the course of a plankton bloom showed that although there were differences between the stations, the time variation in chlorophyll concentration followed broadly the same course at all the stations. The variation between stations in total quantity of chlorophyll in the water column was small enough to indicate that measurements taken at a single station would be quite adequate to study major seasonal trends.

Caloric and Carbon Equivalents of Zooplankton Biomass

In a study throughout 1 year at a station in St. Margaret's Bay, N.S., the caloric content per unit dry weight of zooplankton showed a fivefold variation. Along with all the available information from the literature, the data indicated that the dependence of caloric content of zooplankton (y) on per cent organic matter (x) could be described by the equation y = −3370 + 136 x − 0.514 x2. The caloric content may be predicted from per cent ash (A) and per cent carbon (C) by the equation y = 1351 + 106 C − 21.2 A. The relative stability of the caloric or carbon standing stock of zooplankton per unit water volume, compared with numbers or dry weight, may be an indication of some kind of regulatory mechanism controlling energy flow.