Coordinated Rhythms Of Digestion Absorption And Excretion In Mytilus-Edulis (Bivalvia Mollusca)

Sequential alternation of extracellular digestion in the stomach and intracellular digestion in the diverticula appears widespread among bivalves. The present study documents some physiological consequences of such processes in Mytilus edulis L. collected during 1981 from Whitsand Bay, Cornwall, England. Pronounced temporal fluctuations in faecal deposition are described that relate, in terms of amplitude and period, to both sinusoidal rhythmicity established for ammonia excretion and changes in the morphology of digestive tubules. Although at least partially synchronised among replicate groups of mussels, these cycles bore no consistent relationship with exogenous influences. Hourly fluctuation in the net absorption efficiency for nitrogen, as evidenced by the mean percentage ±2 SE, measured over 24 h sampling periods, was considerable (16.0±53.7, 49.3±10.9 and 52.8±6.6 for mussels acclimated in March, June and October, respectively). This variation in absorption derived from an inverse relationship between the percentage nitrogen within faeces and the rate of faecal egestion. Accordingly, peaks of faecal deposition presumably represented the pulsed remnants of intracellular digestion. Co-ordinated rhythms of digestion, absorption and excretion were thus evident in M. edulis. These processes displayed seasonally dependent periodicities of approximately 8, 3 and 4 h in March, June and October, respectively. It was concluded that, at least for M. edulis, this previously unquantified rhythmicity of physiological processes warrants careful consideration during assays commonly undertaken in the complication of nutrient and energy budgets.

Effects Of Temperature And Salinity On Oxygen-Consumption And Nitrogen-Excretion In Thais (Nucella) Lapillus (L)

The 2-wk TLm of stepwise-acclimated Thais lapillus (L.) (>20 mm long) was 14.2–16.2%. salinity (S) at 5, 10, 15, and 20°C. The same TLm occurred at 10 °C after direct transfer of snails to the final salinity but stepwise-acclimated small snails (<20 mm) tolerated a significantly lower salinity (12.7%. S). Oxygen consumption rates () fit the allometric equation . Salinity and temperature had a significant effect on , which was highest at 30%. S and depressed at 17.5%. S and at 5°C. Ammonia excretion rates fit the allometric equation . Both salinity and temperature affected . Ammonia excretion was significantly lower at 17.5 %. S than at higher salinities at 10, 15, and 20°C, but did not vary as a function of salinity at 5°C. Primary amines were lost from snails under all conditions without any obvious relationship with temperature or salinity. Primary-amine loss, expressed as a percentage of , was significantly higher at 17.5 %. S than at higher salinities. Oxygen : nitrogen ratios ranged from 4.2–15.6, indicating protein was the primary metabolic substrate, and were highest at 15 °C and lowest at 5 °C. Snails withstood 89 days starvation without mortality at 10°C. Oxygen consumption of snails declined by 28% during starvation due to a 37% decline in dry weight; consequently, weight-specific respiration rate increased by 17%. The intercept (a) for the allometric equations did not change during starvation. Ammonia excretion increased during starvation, and primary-amine loss increased until Day 21, then declined. Oxygen: nitrogen ratios declined from 14 to 8, indicating an increased catabolism of protein during starvation.

Aspects Of Microbial Heterotrophic Production In A Highly Turbid Estuary

The uptake of 14C glucose by natural microbial populations has been studied in the Severn Estuary and Bristol Channel, U.K.; the turbidity (suspended solids) in the estuary varied between < 5 mg · 1−1 at the seaward extremity to >800 mg · 1−1 in the estuary proper. The heterotrophic potential, Vm, was found to correlate with turbidity and particulate organic carbon but there was no correlation between microbial biomass, as assessed by plate counts, and turbidity or Vm; measurement of Vm ranged from 0.9 × 10−4 to 288 × 10−4μgC·1−1·h−1 and turnover time from <2 to >100 h. In 17 out of 42 experiments, the uptake of 14C glucose did not conform to Michaelis kinetics and in five of these experiments the data suggested that there may be a threshold of glucose concentration below which there is no uptake.

Determination Of Fine-Scale Vertical-Distribution Of Microbes And Meiofauna In An Intertidal Sediment

A simple sampling device is described which produces thin (1 mm) sections of sediment cores. The sampler has been tested on fine sand of an intertidal sandflat and used to study the vertical distribution, over part of a tidal cycle in August, 1981, of migrating algae in the surface 20 mm of sand. Two species of Diplonies and one of Navicula showed marked changes in vertical distribution as the sandflat was flooded, but the distribution of bacteria in the sime samples did not show any change with tidal state. Spatial separation of different species of harpacticoid oppepods within the surface 20 mm of sand has also been demonstrated using this sampler, and the results suggest that different species may occupy particular fine-scale spatial niches within the sand column. The depth separation of nematode species was less well defined, except for two species with apparently the same feeding mode which were isolated from one another vertically.

Population-Dynamics And Production Of Euphausiids. IV Euphausia-Krohni Nematoscelis-Megalops And Thysanoessa-Gregaria And 8 Rare Species In The North-Atlantic Ocean

Seasonal changes in the abundance, size and occurrence of furciliae of Euphausia krohni (Brandt), Nematoscelis megalops (G. O. Sars) and Thysanoessa gregaria G. O. Sars are described from samples taken at 10 m depth with the Continuous Plankton Recorder (CPR) over a period of 2 yr (January 1966 to December 1967) in the North Atlantic Ocean. E. krohni and T. gregaria were found to breed through most of the year but N. megalops bred only in spring and summer. Annual mean biomass was calculated directly from the data and production was estimated from published P:B ratios. The seasonal occurrences of E. brevis Hansen, E. hemigibba Hansen, E. mutica Hansen, E. tenera Hansen, Stylocheiron longicorne G. O. Sars, S. maximum Hansen, Thysanopoda acutifrons Holt and Tattershall and T. aequalis Hansen in the samples are described.

Continuous Plankton Records - Geographical Variations In Numerical Abundance Biomass And Production Of Euphausiids In The North-Atlantic Ocean And The North-Sea

Geographical variations in the numbers, biomass and production of euphausiids and the contribution of common species to the total are described from samples taken during 1966 and 1967 in the North Atlantic Ocean and the North Sea by the Continuous Plankton Recorder at 10 m depth. Euphausiids were most abundant in the central and western North Atlantic Ocean and the Norwegian Sea. Thysanoessa longicaudata (Krøyer) was numerically dominant. Biomass was greatest in the Norwegian Sea and the north-eastern North Sea where Meganyctiphanes norvegica (M. Sars) accounted for 81 and 59%, respectively, of the total biomass. Production was highest off Nova Scotia and in Iberian coastal waters; the dominant species were T. raschi (M. Sars) in the former area and Nyctiphanes couchi (Bell) in the latter. The mean P:B ratios were correlated with temperature.

Effects Of Preservation On Wet Weight Dry-Weight Nitrogen And Carbon Contents Of Calanus-Helgolandicus (Crustacea Copepoda)

The lengths, wet and dry weights, nitrogen and carbon contents of fresh, frozen and formaldehyde-fixed specimens of Calanus helgolandicus (Claus) were determined. Samples were collected during May 1980 in the Celtic Sea. Individual Copepodite Stages 3, 4, 5, and Adult Male and Female Stage 6 were measured and analysed, and 36 linear regression equations derived for these variables together with mean values, standard deviations and 95% confidence limits. The range of nitrogen values in the fresh material, expressed as a percentage of dry weight, ranged from 8.08%±0.80 (Copepodite Stage 3) to 10.89%±0.27 (adult female); carbon values changed from 41.6%±3.05 (mean ±95% confidence limits) for Copepodite Stage 3 to 50.97%±2.63 in Copepodite Stage 5. The adult females had a high nitrogen and relatively low carbon content, while the converse was true for Stage 5 copepodites. There was a loss of dry weight from the frozen samples (57%) and the fixed samples (38%) compared with the mean of the fresh dry weight of all stages. The material lost from the copepods was rich in nitrogen, thus, artificially high percentage carbon values were determined from the frozen and fixed samples (52.0 to 60.3% and 44.7 to 58.5%, respectively).

Variability In Abundance Vertical-Distribution And Ontogenetic Migrations Of Thysanoessa-Longicaudata (Crustacea Euphausiacea) In The Northeastern Atlantic-Ocean

The vertical distribution, seasonal and ontogenetic migrations and seasonal variability in abundance of Thysanoessa longicaudata (Krøyer) were investigated using the Longhurst-Hardy Plankton Recorder for a 4 yr period (March, 1971 to May, 1975) at Ocean Weather Station “I” (59°00′N; 19°00′W) in the north-eastern Atlantic Ocean. Of 8 species of euphausiids identified at this position, the vast majority were T. longicaudata (for example, 99.5% of the total euphausiids in 1972 belonged to this species). From March to October the majority of calyptopes, furciliae and adults of T. longicaudata were found in the upper 100 m. The major spawning occurred in spring at a water temperature of 9° to 10°C and calyptopes and furciliae appeared in late April, reaching their maximum abundance in May. There was no evidence of large-scale diurnal migrations, although an extensive ontogenetic migration of young developmental stages was observed. The eggs were found from 100 m down to 800 m, the maximum depth of sampling, and the vertical distribution of the three naupliar stages showed a “developmental ascent” as they matured. During the main reproductive period in May, over 70% of all nauplii were below 500 m while more than 94% of Calyptopis Stage I were above 500 m with their maximum abundance in the euphotic zone (0 to 50 m). Calyptopis Stage I is the first feeding stage and it is this stage which shows the largest ontogenetic migration. Brief descriptions of the egg and nauplii are given.

Responses Of Mytilus-Edulis On Exposure To The Water-Accommodated Fraction Of North-Sea-Oil

Individuals of Mytilus edulis L., collected from the Erme estuary (S.W. England) in 1978, were exposed to low concentrations (7 to 68 μg l-1) of the water-accommodated fraction (WAF) of North Sea crude oil. The pattern of accumulation of petroleum hydrocarbons in the body tissues was affected by the presence of algal food cells, the period of exposure, the hydrocarbon concentration in seawater, the type of body tissue and the nature of the hydrocarbon. Many physiological responses (e.g. rates of oxygen consumption, feeding, excretion, and scope for growth), cellular responses (e.g. lysosomal latency and digestive cell size) and biochemical responses (e.g. specific activities of several enzymes) were significantly altered by short-term (4 wk) and/or long-term (5 mo) exposure to WAF. Stress indices such as scope for growth and lysosomal latency were negatively correlated with tissue aromatic hydrocarbons.

Population-Dynamics And Production Of Euphausiids. III Meganyctiphanes-Norvegica And Nyctiphanes-Couchi In The North-Atlantic Ocean And The North-Sea

Seasonal changes in abundance, size and aspects of the population structure of Meganyctiphanes norvegica (M. Sars) and Nyctiphanes couchi (Bell) are described from samples taken with the “Continuous Plankton Recorder” at 10 m depth over a 2 yr period (1966 and 1967) in the North Atlantic Ocean and the North Sea. M. norvegica lived for a maximum of just over 2 yr, and adults of both year-classes spawned during a limited breeding season in the spring or summer. N. couchi spawned over a prolonged breeding season, giving rise to a complex of cohorts with overlapping size ranges. It was concluded that 3 or 4 cohorts were spawned in each year and that the maximum life span was probably greater than 1 yr, although maturity may be attained in less than a year. Estimated annual production at 10 m depth for M. norvegica ranged from 0.80 to 18.74 mg m-3yr-1 and for N. couchi from 0.67 to 8.23 mg m-3yr-1. P:B ratios ranged from 1.3:1 to 6.3:1 for M. norvegica and 4.0:1 to 5.5:1 for N. couchi.

Continuous Plankton Records - Persistence In Time-Series And The Population-Dynamics Of Pseudocalanus-Elongatus And Acartia-Clausi

Rates of population increase in early spring and the sizes of overwintering stocks were calculated for the planktonic copepods Pseudocalanus elongatus and Acartia clausi for a set of areas covering the open waters of the north-east Atlantic Ocean and the North Sea for the period 1948 to 1979. For both species, the rates of population increase were higher in the open ocean than in the North Sea and appear to be related to temperature. The overwintering stocks in the North Sea were larger than those in the open ocean and are probably related to phytoplanton concentration. P. elongatus shows higher overwintering stocks and lower rates of population increase than A. clausi, resulting in different levels of persistence in the stocks of the two species. It is suggested that this difference in persistence is responsible for differences between the two species with respect to geographical distribution in summer and different patterns of year-to-year fluctuations in abundance.