Joel C. Goldman

Nitrogenous Nutrition of Marine Phytoplankton in Nutrient-Depleted Waters

Variability in the small-scale temporal and spatial patterns in nitrogenous nutrient supply, coupled with an enhanced uptake capability for nitrogenous nutrients induced by nitrogen limitation, make it possible for phytoplankton to maintain nearly maximum rates of growth at media nutrient concentrations that cannot be quantified with existing analytical techniques.

Outdoor algal mass cultures—II. Photosynthetic yield limitations☆

The photosynthetic conversion of sunlight energy into algal biomass in large-scale outdoor cultures is controlled by the availability of sunlight, the photosynthetic machinery of algae, nutrients, temperature and the design characteristics of the culture system. For the situation in which light is made the growth rate limiting factor, there is an upper limit in the light conversion efficiency of a large-scale culture, which translates to a maximum potential yield of 30—40g dry wt m2 day1 under ideal sunlight conditions. In practice, the best yield data for outdoor cultures in various locations in the world has been 30–40g dry wt m−2 day−1 for short periods and considerably less for longer durations. The development of large-scale mass cultures involves many considerations, but the two major design parameters for optimizing yields at a particular time of year are the flow rate through the culture and the depth.

Potential role of large oceanic diatoms in new primary production

Very large phytoplankton species >50 μm in size, particularly diatoms, generally are found in background numbers throughout the euphotic zone of oceanic waters. Yet, when responding to episodic injections of new nutrients across the nutricline at the base of the euphotic zone these phototrophs may make a disproportionately large contribution to new primary production. To test this concept, we isolated a group of large diatoms from the Sargasso Sea and found that the specific growth rate of several of these species in culture was great enough at the ≈2% light level in oligotrophic waters to meet the requirements of several hypothetical scenarios in which annual rates of new production from the sum of one or more episodic blooms were equal to contemporary estimates. Two of the fast-growing species, Stephanopyxis palmeriana (Greville) Grunow and Pseudoguinardia recta von Stosch, formed giant flocculant masses while growing. Such masses could sink rapidly out of the euphotic zone or be a direct food source for invertebrates or fish higher up the food chain. Not only would a short, simple trophic system with low losses result, but the events would virtually be impossible to observe with conventional sampling.

Physiological Processes, Nutrient Availability, and the Concept of Relative Growth Rate in Marine Phytoplankton Ecology

After more than thirty years of intensive research in phytoplankton ecology, our knowledge of how to measure accurately growth rates of photosynthetic organisms in nature is still very limited (1–3). Difficulties in extrapolating results from in situ bottle tests involving standard rate-measuring incubation methods (such as the 14C-labelling technique) are becoming increasingly evident (3–6); hence, we now are faced with conflicting opinions regarding the magnitude of phytoplankton growth rates in the marine environment (5,7–10).

Experimental studies on an omnivorous microflagellate: implications for grazing and nutrient regeneration in the marine microbial food chain

Abstract A phagotrophic marine microflagellate Paraphysomonas imperforata was found to graze on a wide assortment of phytoplankton species as well as bacteria; it also resorted to cannibalism when food was in short supply. Growth rates of the microflagellate were higher than those of the phytoplankton prey, although in some cases lower measured growth rates were found when there was aggregation of cells. This aggregation seemed to be bacterially mediated. The ratio of predator to prey cell length varied from about 2 for the phytoplankton prey to 7 for bacteria. Nitrogen regeneration by the microflagellate, primarily as NH 4 + , never exceeded 50% of the nitrogen originally incorporated by the phytoplankton and bacterial prey. The role of bacteria in regenerating nutrients was found to be minimal relative to microflagellates. These results imply that both omnivory by small protozoa and a greater flexibility in the relationship between predator and prey sizes should be incorporated into the contemporary “microbial food loop” concept. In addition, to achieve nutrient regeneration efficiencies in pelagic surface waters of 80–90%, as is generally believed to occur, requires that the microbial food web be exceedingly complex with a hierarchy of at least several grazing steps. Alternatively, nutrient regeneration efficiencies in surface waters may be lower than envisioned.

Outdoor algal mass cultures—I. Applications☆

Abstract Algal mass culturing research has been carried out in many parts of the world for past 30 yr. Whereas early efforts were directed towards single-celled protein production for human consumption, many new applications have evolved including wastewater treatment, water renovation, nutrient recycling, production of chemicals, aquaculture and bioconversion of solar energy. Photosynthetic yields over 30g dry wt m −2 day −1 have been attained on occasion in many locations for short periods and yields between 15 and 25 g dry wt m −2 day −1 for longer periods are now common. It appears that bioconversion of solar energy with algal cultures is not attractive because of the tremendous quantities of land, water and nutrients required. Similarly, single-celled protein from microalgae is beset with numerous problems associated with nutritional quality, toxicology and economics. The main attractiveness of algal mass cultures is that they have great versatility to be integrated into multi-use systems for simultaneously solving several environmental problems. Their use probably will be limited to small specific applications and not on the massive scale projected in the past.

Spatial and Temporal Discontinuities of Biological Processes in Pelagic Surface Waters

The classical paradigm of an unproductive, nutrient-poor pelagic zone where primary production is fueled almost exclusively by nutrient regeneration processes, appears at odds with the contemporary view that new primary production, supported by a stoichiometric input of oxidized nutrients into the euphotic zone, is considerably higher than previously thought. One way to accomodate both scenarios is to invoke the two layer concept in which the bulk of new primary production occurs at or near the base of the euphotic zone in response to pulsed injections of NO3 - and PO4 3-. Productivity in the upper euphotic zone where nutrients and biomass are trapped would be regulated almost exclusively by regenerative and degradative processes that occur within the microbial food loop. Since the microbial food loop which consists of a tightly-knit assemblage of phototrophic and heterotrophic nanno- and picoplankton persists throughout the euphotic zone, most of the energy and carbon processed by these small microbes would be lost through respiration and thus would not contribute to new production exiting to deeper waters. This raises the perplexing question of how biological processes are coupled to the input of new nutrients which, in turn, is controlled by physical events that occur on greatly varying temporal and spatial scales. Possibly, short-lived, local mixing events provide the right combination of light and new nutrients to allow rapid and undetected bursts of growth of larger phytoplankton species, in effect, creating ephemeral eutrophication zones. The resulting food chain may be short and simple so that newly fixed carbon can exit the euphotic zone rapidly while leaving behind an oxygen signal.

Susceptibility of some marine phytoplankton species to cell breakage during filtration and post-filtration rinsing

Abstract Several fragile phytoplankton species among a diverse group of 13 species were found to be very susceptible to cell breakage when exposed to the air under vacuum between the filtration and rinsing steps used to terminate 14C fixation experiments and remove residual [ 14 C]HCO 3 − . Up to 60% of fixed carbon after 15-min incubation was found in the rinse. Losses were even greater when cultures were pulsed with NH 4 + at the start of the incubation, probably because rapid NH 4 + uptake leads to the accumulation of large pool of soluble and low molecular weight compounds. Most likely, the cells, when exposed to the air, are subject to extreme osmotic shock and rupture. Unaccountable losses of 14 C occurred with polycarbonate filiters relative to glass-fiber filters. In addition, vacuum pressure differentials >25–100 mmHg across polycarbonate filters also caused cell breakage that led to the accumulation of 14 C in the filtrate. Avoiding air exposure of the filter between the filtration and rinsing steps or eliminating the rinsing step entirely and acid-soaking or fuming the filters led to virtually complete recovery of fixed carbon. Our results based on 15-min incubations may not be directly comparable with longer-term incubations, but they do serve highlight our concerns about filtration procedures in general.

Physical models of integrated waste recycling- marine polyculture systems

Abstract A combined tertiary sewage treatment—marine aquaculture system has been developed, tested and evaluated using several different experimental sizes and configurations located both at Woods Hole, Mass. and Fort Pierce, Fla. Domestic wastewater effluent from secondary sewage treatment, mixed with sea water, is used as a source of nutrients for growing unicellular marine algae and the algae, in turn, are fed to oysters, clams, and other bivalve molluscs. Solid wastes from the shellfish are fed upon by polychaete worms, amphipods, and other small invertebrates that serve as food for flounder, lobsters, and other commercially valuable secondary crops. Dissolved wastes excreted by the shellfish and other animals and any nutrients not initially removed by the univellular algae are removed by various species of commercial red seaweeds (Chondrus, Gracilaria, Agardhiella, Hypnea) as a final ‘polishing’ step. The final effluent from the system is virtually free of inorganic nitrogen and is incapable of supporting further growth of marine life or of contributing to eutrophication of the receiving waters. A description of experiments with the above food chains and preliminary results with some alternative approaches are discussed, including a detailed account of the nitrogen mass balance through all of the components of one of the experimental systems.

Experimental demonstration of the roles of bacteria and bacterivorous protozoa in plankton nutrient cycles

We have used a model food chain composed of a natural bacterial assemblage, a pennate diatom and a bacterivorous microflagellate to investigate the factors controlling the relative importance of bacteria and protozoa as sources for regenerated nitrogen in plankton communities. In bacterized diatom cultures in which diatom growth was nitrogen-limited, the carbon:nitrogen (C:N) ratio of the bacterial substrate greatly affected which population was responsible for the uptake of nitrogen. When nitrogen was added as NH4+ and the cultures were supplemented with glucose, the bacteria competed successfully with the algae for NH4+ and prevented the growth of algae by rapidly assimilating all NH4+ in the cultures. Bacterivorous protozoa inoculated into these cultures grazed the bacterial population and remineralized NH4+, thus relieving the nitrogen limitation of algal growth and allowing an increase in algal biomass. In contrast, bacteria in cultures supplemented with the amino acid glycine (C:N = 2) were major remineralizers of nitrogen, and the influence of protozoan grazing was minimal. We conclude that the relative importance of bacteria and protozoa as nutrient regenerators in the detrital food loop is dependent largely on the overall carbon:nutrient ratio of the bacterial substrate. The role of bacterivorous protozoa as remineralizers of a growth-limiting nutrient is maximal in situations where the carbon:nutrient ratio of the bacterial substrate is high.