Aspects of 14CO2-fixation by endosymbiotic rhodoplasts in the marine opisthobranchiate Hermaea bifida

When the marine opisthobranchiate slug Hermaea bifida Mont. is incubated in a H¹⁴CO ₃ ^- -seawater medium in the light, a considerable net gain of ¹⁴C-assimilates is observed. Electron microscopic control provided evidence that this ¹⁴C-fixation is due to photosynthesis by chloroplasts (=rhodoplasts) endosymbiotic in the cells of the digestive gland of the slug. After thin-layer chromatographic analysis various ¹⁴C-labelled photosynthates could be traced. The assimilate pattern of the rhodoplasts is compared with that of the marine red alga Griffithsia flosculosa (Ellis) Batt., from which the plastids are acquired by feeding. The nutritional relationship of this endosymbiosis is discussed, with emphasis on the occurrence of functional chloroplast endosymbioses among the eolidiform species of the Sacoglossa.     

Algen/Wirbellosen-Endosymbiosen

Symbioses between unicellular algae and aquatic invertebrates are a widespread biological phenomenon including animal partners ranging from Protozoa up to the Urochordata and algae from at least eight different classes. The establishment of an endosymbiosis encompasses several phases such as surface contact, phagocytosis, cellular recognition, sequestration and regulation. Various levels of integration are observed, all resulting in mutually beneficial interactions. Some animal partners fully rely on the nutritive contribution by their algal endosymbionts and thus become functional photoautotrophs. The particular structural and physiological features of an array of endosymbioses are discussed.     

A three-trophic level estuarine model: Synergism of two mechanistic simulations

Few numerical simulations have attempted to include a high degree of biological detail for several trophic levels. Typically, in planktonic ecosystem models, if the dynamics of nutrients, phytoplankton and herbivorous zooplankton are formulated with ecological complexity, then carnivores are ignored, forced or modeled in an extremely simplified manner. Extensive mechanistic detail for important carnivores is difficult to represent because reliable and relevant ecological data are rarely available for appropriate species and local populations. Further, the wide temporal and spatial differences between life histories of lower plankton and carnivores may be technically difficult to model.In Narragansett Bay, Rhode Island, the ctenophore Mnemiopsis leidyi is an important carnivore to which these objections do not apply. A detailed carbon-based simulation model of this population of ctenophores was developed independently from an ecosystem model of Narragansett Bay which included detailed interactions between phytoplankton, primarily herbivorous zooplankton and nutrients. The interfacing of these two models without changing any of the formulations or values of the coefficients provided a test of the commonly used practice of forcing certain components. Both models were originally constructed with the biomass of a critical compartment forced according to observed data; in the plankton model, ctenophores were forced, and in the ctenophore model, zooplankton were forced.Predicted biomasses for zooplankton and ctenophores in the combined model were similar to the results of the two parent models, but improved relative to the actual field observations. From the findings it appears that the strategy of forcing is valid provided the forced patterns are appropriate and reasonable.     

Assessing Uncertainty in Estimates of Nitrogen Loading to Estuaries for Research, Planning, and Risk Assessment

Parametric (propagation for normal error estimates) and nonparametric methods (bootstrap and enumeration of combinations) to assess the uncertainty in calculated rates of nitrogen loading were compared, based on the propagation of uncertainty observed in the variables used in the calculation. In addition, since such calculations are often based on literature surveys rather than random replicate measurements for the site in question, error propagation was also compared using the uncertainty of the sampled population (e.g., standard deviation) as well as the uncertainty of the mean (e.g., standard error of the mean). Calculations for the predicted nitrogen loading to a shallow estuary (Waquoit Bay, MA) were used as an example. The previously estimated mean loading from the watershed (5,400 ha) to Waquoit Bay (600 ha) was 23,000 kg N yr⁻¹. The mode of a nonparametric estimate of the probability distribution differed dramatically, equaling only 70% of this mean. Repeated observations were available for only 8 of the 16 variables used in our calculation. We estimated uncertainty in model predictions by treating these as sample replicates. Parametric and nonparametric estimates of the standard error of the mean loading rate were 12–14%. However, since the available data include site-to-site variability, as is often the case, standard error may be an inappropriate measure of confidence. The standard deviations were around 38% of the loading rate. Further, 95% confidence intervals differed between the nonparametric and parametric methods, with those of the nonparametric method arranged asymmetrically around the predicted loading rate. The disparity in magnitude and symmetry of calculated confidence limits argue for careful consideration of the nature of the uncertainty of variables used in chained calculations. This analysis also suggests that a nonparametric method of calculating loading rates using most frequently observed values for variables used in loading calculations may be more appropriate than using mean values. These findings reinforce the importance of including assessment of uncertainty when evaluating nutrient loading rates in research and planning. Risk assessment, which may need to consider relative probability of extreme events in worst-case scenarios, will be in serious error using normal estimates, or even the nonparametric bootstrap. A method such as our enumeration of combinations produces a more reliable distribution of risk.     

Metabolism of epipelagic tropical ctenophores

Measurements of respiration and excretion at 25°C were made for five species of ctenophores collected during five cruises to the Bahamas (1982–1984). The mean element-specific respiration and ammonium excretion rates of freshly collected specimens of all species ranged from 4 to 16% d^-1, the mean atomic O:N ratios were 10 to 16, and ammonium averaged 60 to 90% of the total dissolved nitrogen excreted. For adult ctenophores, the carbon content ranged from 0.6% carbon (as percent of dry weight) for Bolinopsis vitrea to 3.7% carbon for Beroë ovata. There was a marked increase in the organic content (% carbon of dry weight) of small Bolinopsis vitrea with tentacles compared to fully lobate adults. B. vitrea had increasingly higher metabolic rates when held at food concentrations up to 100 copepods 1^-1 (about 250 g C 1^-1). The overall range between starved and well-fed B. vitrea was about two times for respiration and a factor of three for ammonium excretion. B. vitrea decreased from well-fed to a starved metabolic rate in about a day after removal from food. The metabolic rate of Eurhamphaea vexilligera was not measurably affected by short-term starvation or feeding (maximum 25 copepods 1^-1). In feeding experiments, E. vexilligera of 20 to 56 mm length fed at rates equivalent to clearance rates of 250 to 1 800 ml h^-1.     

14CO2-Fixation by the endosymbiotic alga Platymonas convolutae within the turbellrian Convoluta roscoffensis

Photosynthetic assimilation of ¹⁴CO₂ by the symbiotic green alga Platymonas convolutae Parke et Manton in the marine flatworm Convoluta roscoffensis Graff has been investigated and compared with that in free-living P. subcordiformis and P. tetrathele. All Platymonas species investigated rapidly incorporate ¹⁴CO₂ into a complex variety of soluble and insoluble assimilates. The rate of dark fixation is considerably lower in P. convolutae. Typical ¹⁴C-assimilate patterns are rather uniform in all Platymonas species, but the time courses of ¹⁴C-labelling of several compounds are very different. The percentage of ¹⁴C-aspartate and ¹⁴C-malate is significantly higher in P. convolutae after short-term-photosynthesis, whereas ¹⁴C-labelled phosphate esters predominate in the free-living Platymonas species. A comparison of the kinetics of ¹⁴C-labelling and of the distribution of ¹⁴C-activity between soluble and insoluble fractions suggests that glucose and fructose, not mannitol, as well as several amino acids (especially alanine) move from the algal partner to the tissue of the animal host. The significance of these findings is discussed.     

Toxische Planktonalgen

Plankton algae occasionally produce water blooms in which cell density may be so high as to colour the water reddish or yellow-brown. Some of these organisms exhibit considerable toxicity. While the marine toxic species belong almost exclusively to the dinoflagellates, toxin producers of limnic habitats are mostly blue-green algae. Some chemical and pharmacological properties of algal toxins are discussed.     

Urban Ecosystem Services for Resilience Planning and Management in New York City

We review the current state of knowledge about urban ecosystem services in New York City (NYC) and how these services are regulated, planned for, and managed. Focusing on ecosystem services that have presented challenges in NYC—including stormwater quality enhancement and flood control, drinking water quality, food provisioning and recreation—we find that mismatches between the scale of production and scale of management occur where service provision is insufficient. Adequate production of locally produced services and services which are more accessible when produced locally is challenging in the context of dense urban development that is characteristic of NYC. Management approaches are needed to address scale mismatches in the production and consumption of ecosystem services. By coordinating along multiple scales of management and promoting best management practices, urban leaders have an opportunity to ensure that nature and ecosystem processes are protected in cities to support the delivery of fundamental urban ecosystem services.