Environmental selection and resource allocation determine spatial patterns in picophytoplankton cell size

Here we describe a new trait-based model for cellular resource allocation that we use to investigate the relative importance of different drivers for small cell size in phytoplankton. Using the model, we show that increased investment in nonscalable structural components with decreasing cell size leads to a trade-off between cell size, nutrient and light affinity, and growth rate. Within the most extreme nutrient-limited, stratified environments, resource competition theory then predicts a trend toward larger minimum cell size with increasing depth. We demonstrate that this explains observed trends using a marine ecosystem model that represents selection and adaptation of a diverse community defined by traits for cell size and subcellular resource allocation. This framework for linking cellular physiology to environmental selection can be used to investigate the adaptive response of the marine microbial community to environmental conditions and the adaptive value of variations in cellular physiology.

Unbiased Linear Property Estimation For Spheres From Sections Exhibiting Overprojection And Truncation

In the biological sciences, stereological techniques are frequently used to infer changes in structural parameters (volume fraction, for example) between samples from different populations or subject to differing treatment regimes. Non-homogeneity of these parameters is virtually guaranteed, both between experimental animals and within the organ under consideration. A two-stage strategy is then desirable, the first stage involving unbiased estimation of the required parameter, separately for each experimental unit, the latter being defined as a subset of the organ for which homogeneity can reasonably be assumed. In the second stage, these point estimates are used as data inputs to a hierarchical analysis of variance, to distinguish treatment effects from variability between animals, for example. Techniques are therefore required for unbiased estimation of parameters from potentially small numbers of sample profiles. This paper derives unbiased estimates of linear properties in one special case—the sampling of spherical particles by transmission microscopy, when the section thickness is not negligible and the resulting circular profiles are subject to lower truncation. The derivation uses the general integral equation formulation of Nicholson (1970); the resulting formulae are simplified, algebraically, and their efficient computation discussed. Bias arising from variability in slice thickness is shown to be negligible in typical cases. The strategy is illustrated for data examining the effects, on the secondary lysosomes in the digestive cells, of exposure of the common mussel to hydrocarbons. Prolonged exposure, at 30 μg 1−1 total oil-derived hydrocarbons, is seen to increase the average volume of a lysosome, and the volume fraction that lysosomes occupy, but to reduce their number.

The Application Of Radioisotopes In The Study Of Estuarine Sedimentary Processes

The spatial and temporal distributions of some radionuclides in effluents originating from the British Nuclear Fuels Ltd (BNFL) reprocessing plant at Windscale, which are released into the Irish Sea, have been studied in sediments at 16 sites in the salt marsh region near Newbiggin on the Esk estuary Cumbria, England. The concentration of non-conservative radionuclides in surface sediments of the area cannot be described by a single parameter, but there is a high correlation with organic C, Cu, Al and the Si : Al ratio with particle size. The preservation of the historical record of the BNFL effluents in the Esk sediments is dependent on the hydrology of the area, as it effects such processes as accretion, erosion and remixing. From the 106Ru and 210Po concentrations and the 137Cs : 134Cs ratio in the sediment profiles with depth, we have identified these processes. Sedimentation rates at sites of accretion vary between 0·5 and 3 cm year−1. However, at some sites they appear to be much higher, approximately 6 cm year−1 in the top 10 cm, but they are not consistent throughout the depth profiles. This may be a true reflection of variable accretion related to sediment type, or one which is influenced by surficial mixing. Some cores showed evidence of continuous accretion but no significant radioactivity was detected at depths below 35–40 cm, indicating an overall sedimentation rate of approximately 1·5 cm year−1 for the 25–30-year period since BNFL effluents first entered the Irish Sea.

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.

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.