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.

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.

Plankton Of The Fladen Ground During Flex-76 .3. Vertical-Distribution Population-Dynamics And Production Of Calanus-Finmarchicus (Crustacea Copepoda)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR), the Longhurst Hardy Plankton Recorder (LHPR) and by our colleagues from other participating Institutes during the Fladen Ground Experiment (FLEX 76) were used to describe the vertical distribution and population dynamics of Calanus finmarchicus (Gunnerus) and to provide estimates of the production and carbon budget of the population from 19 March to 3 June, 1976. Total production of the 19 March to 3 June, 1976. Total production of the nauplii and copepodite stages (including adults), during the exponential growth phase in May, was estimated to be in the range of 0.49 to 0.91 g C m-2 d-1 or 29.0 to 55 g dry wt m-2 (14.5 to 27.8 g C m-2) for the three successive 10 d periods in May. Two gross growth efficiencies (K 1) (20 and 34%), together with the lower value of C. finmarchicus production, were used to calculate the gross ingestion levels of algae as 2.45 and 1.44 g C m-2 d-1 (73.5 and 43.2 g C m-2 over the May period). These ingestion levels, together with the algae ingested by other zooplankton species, are greater than the estimated total phytoplankton production of 45.9 g C m-2 over the FLEX period. A number of factors are discussed which could explain the discrepancies between the production estimates. One suggestion is that the vertical distribution of the development stages of this herbivorous copepod and their diel and ontogenetic migration patterns enable it to efficiently exploit its food source. Data from the FLEX experiment indicated that the depletion of nutrients limited the size of the spring bloom, but that it was the grazing pressure exerted by C. finmarchicus which was responsible for the control and depletion of the phytoplankton in the spring of 1976 in the northern North Sea.

Population-Dynamics And Production Of Euphausiids .2. Thysanoessa-Inermis And Thysanoessa-Raschi In The North-Sea And American Coastal Waters

Results from the Continuous Plankton Recorder (CPR) survey for 1966 and 1967 are used to describe seasonal changes in abundance, size and aspects of the population structure of Thysanoessa inermis (Krøyer) and T. raschi (M. Sars) at a depth of 10 m in the North Sea and in American coastal waters from the Grand Banks to the Gulf of Maine. Production and dry weight were estimated from these data. Two year-groups were usually present in the breeding population, the proportion surviving into a second year being higher in American waters than in the North Sea. Annual production for each species was within the range 0.69 to 4.66 mg m-3 and the ratio between production and biomass (P:B) was between 1.3 and 4.2; values outside these ranges were obtained only for American coastal waters in 1967, when the frequency of sampling was low.

Plankton Of The Fladen Ground During Flex-76 .2. Population-Dynamics And Production Of Thysanoessa-Inermis (Crustacea Euphausiacea)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR) and the Longhurst-Hardy Plankton Recorder (LHPR) during the Fladen Ground Experiment in 1976 (FLEX 76) are used to describe the vertical distribution and population dynamics of Thysanoessa inermis (Krøyer) and to provide estimates of the production and carbon budget of the population from 19th March to 3 June 1976. Spawning occurred in late April and early May, in near synchronisation with the start of the spring bloom of phytoplankton. Eggs, nauplii and calyptopes reached maximum abundance in succession, and furciliae were numerous when sampling ceased in early June. Adults increased in length from a mean of 12.1 mm in mid-March to 17.5 mm in early June and the estimated production was 2.40 mg m-3 over the 74 d period. Total carbon ingested by the population of T. inermis was estimated to be 10 mg C m-2 d-1 in the upper 100m which was only 1.5% of the daily primary production of 0.68 gC m-2 measured over the FLEX period 26 March to 4 June 1976. The grazing by T. inermis on the phytoplankton population was assumed to have little effect on the control and depletion of the spring phytoplankton bloom during FLEX 77.

Population-Dynamics Of Mytilicola-Intestinalis In Mytilus-Edulis In South West England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.

Ecological effects of the North Atlantic oscillation

Climatic oscillations as reflected in atmospheric modes such as the North Atlantic Oscillation (NAO) may be seen as a proxy for regulating forces in aquatic and terrestrial ecosystems. Our review highlights the variety of climate processes related to the NAO and the diversity in the type of ecological responses that different biological groups can display. Available evidence suggests that the NAO influences ecological dynamics in both marine and terrestrial systems, and its effects may be seen in variation at the individual, population and community levels. The ecological responses to the NAO encompass changes in timing of reproduction, population dynamics, abundance, spatial distribution and interspecific relationships such as competition and predator-prey relationships. This indicates that local responses to large-scale changes may be more subtle than previously suggested. We propose that the NAO effects may be classified as three types: direct, indirect and integrated. Such a classification will help the design and interpretation of analyses attempting to relate ecological changes to the NAO and, possibly, to climate in general.

Spatial demography of Calanus finmarchicus in the Irminger Sea

Continuous Plankton Recorder data suggest that the Irminger Sea supports a major proportion of the surface-living population of the copepod Calanus finmarchicus in the northern North Atlantic, but there have been few studies of its population dynamics in the region. In this paper, we document the seasonal changes in the demographic structure of C finmarchicus in the Irminger Sea from a field programme during 2001/2002, and the associations between its developmental stages and various apparent bio-physical zones. Overwintering stages were found widely at depth (>500 m) across the Irminger Sea, and surviving females were widely distributed in the surface waters the following spring. However, recruitment of the subsequent generation was concentrated around the fringes of the Irminger Sea basin, along the edges of the Irminger and East Greenland Currents, and not in the central basin. In late summer animals were found descending back to overwintering depths in the Central Irminger Sea. The key factors dictating this pattern of recruitment appear to be (a) the general circulation regime, (b) predation on eggs in the spring, possibly by the surviving GO stock, and (c) mortality of first feeding naupliar stages in the central basin where food concentrations appear to be low throughout the year. We compared the demographic patterns in 2001/2002 with observations from the only previous major survey in 1963 and with data from the Continuous Plankton Recorder (CPR) surveys. In both previous data sets, the basic structure of GO ascent from the central basin and G1 recruitment around the fringes was a robust feature, suggesting that it is a recurrent phenomenon. The Irminger Sea is a complex mixing zone between polar and Atlantic water masses, and it has also been identified as a site of sporadic deep convection. The physical oceanographic characteristics of the region are therefore potentially sensitive to climate fluctuations. Despite this, the abundance of C finmarchicus in the region, as measured by the CPR surveys, appears not to have responded to climate factors linked to the North Atlantic Oscillation Index, in contrast with the stocks in eastern Atlantic areas. We speculate that this may because biological factors (production and mortality), rather than transport processes are the key factors affecting the population dynamics in the Irminger Sea. (c) 2007 Elsevier Ltd. All rights reserved.

Quantifying ecosystem-level consequences of ocean acidification and warming by scaling up individual level responses of a predator snail and its trophic interactions

Understanding long‐term, ecosystem‐level impacts of climate change is challenging because experimental research frequently focuses on short‐term, individual‐level impacts in isolation. We address this shortcoming first through an interdisciplinary ensemble of novel experimental techniques to investigate the impacts of 14‐month exposure to ocean acidification and warming (OAW) on the physiology, activity, predatory behaviour and susceptibility to predation of an important marine gastropod (Nucella lapillus). We simultaneously estimated the potential impacts of these global drivers on N. lapillus population dynamics and dispersal parameters. We then used these data to parameterize a dynamic bioclimatic envelope model, to investigate the consequences of OAW on the distribution of the species in the wider NE Atlantic region by 2100. The model accounts also for changes in the distribution of resources, suitable habitat and environment simulated by finely resolved biogeochemical models, under three IPCC global emissions scenarios. The experiments showed that temperature had the greatest impact on individual‐level responses, while acidification had a similarly important role in the mediation of predatory behaviour and susceptibility to predators. Changes in Nucella predatory behaviour appeared to serve as a strategy to mitigate individual‐level impacts of acidification, but the development of this response may be limited in the presence of predators. The model projected significant large‐scale changes in the distribution of Nucella by the year 2100 that were exacerbated by rising greenhouse gas emissions. These changes were spatially heterogeneous, as the degree of impact of OAW on the combination of responses considered by the model varied depending on local‐environmental conditions and resource availability. Such changes in macro‐scale distributions cannot be predicted by investigating individual‐level impacts in isolation, or by considering climate stressors separately. Scaling up the results of experimental climate change research requires approaches that account for long‐term, multiscale responses to multiple stressors, in an ecosystem context.