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We measured biomass yields of 17 clones of marine phytoplankton in media with different concentrations of iron. The biomass yields of all the clones except two were limited by iron. All cyanobacteria tested were dead at iron concentration of 10−9 M, still limited severely at up to 10−7 M. Coastal dinoflagellates showed evident limitation of biomass yield by iron. Different levels of biomass yield limitations were found among the seven coccolithophorid clones. Among other clones, Micromonas (A2167) was only slightly limited by low concentrations of iron, while Heterosigma akashiwo (OLISTH) showed no growth below 10−10 M. In two oceanic clones, Mantoniella sp. (MC-1) and Umbilicosphaera (A2390), no significant limitation of biomass yields were measured at all the different concentrations of iron.

Our objectives were to determine: 1) the influence of different N forms (NH4 +, NO3, and urea) on the growth rate and on the nitrogen and carbon content of four microalgae, and 2) to relate the N form-induced physiological and biochemical differences to a shortage in energy (presumably reductant for NO3 − reduction), or a rate-limiting step in the N uptake and/or assimilation. The use of NO3 − instead of NH4 + resulted in a decrease in growth rate in Thalassiosira pseudonana and in significantly smaller N quotas and higher C:N ratios in T. pseudonana and Chaetoceros gracilis. Growth on urea instead of NH4 + resulted in a lower growth rate in C. gracilis and Gymnodinium sanguineum and in a lower N quota and a higher C:N ratio in most species tested. Growth on NO3 − rather than on NH4 + often resulted in a smaller (less chlorophyll a cell−1) and less efficient (lower quantum yield for oxygen production, higher chlorophyll a fluorescence yield) photosynthetic system, suggesting that NO3 −-grown cells were not energy-limited. On the other hand, since urea-grown cells have a reductant requirement similar to that of NH4 +-grown cells, the urea-induced decrease in growth rate and/or N quotas cannot be attributed to reductant limitation. The rate-limiting step for growth is more likely the activity of nitrate reductase (NR), nitrite reductase (NiR), or urease. Our results also show that symptoms of N limitation in algae (low N quotas, high C:N ratios) may be introduced by the N form, even at saturating N concentrations.

Growth studies were undertaken with two diatoms, the oceanic diatom Thalassiosira oceanica and the estuarine species Thalassiosira pseudonana, using radiolabelled 55Fe in Gulf Stream seawater having an EDTA-trace metal buffer. Intracellular Fe in exponentially growing cells was determined following treatment with titanium(III) EDTA-citrate reducing solution to dissolve adsorbed and noncellular iron. The two species showed different growth responses. T. oceanica grows at its maximum rate over a wide range of Fe concentration. Growth rate is reduced slightly (less than 20%) at the lowest Fe levels. Such low levels result in the growth rate of T. pseudonana dropping to almost zero. T. pseudonana shows a graded response to increased Fe, and a maximum growth rate that is 50% greater than that of T. oceanica. Fast growth by T. oceanica at lowest Fe levels is explained almost entirely by a much lower cell Fe requirement, or quota, rather than by more effective transport at low Fe conditions. T. oceanica cells at near-maximum specific growth rate of 1 day−1 have a cellular iron:carbon ratio of about 2 × 10−6. T. pseudonana at the same growth rate requires several times this amount, and even more at its highest growth rate. Cellular Fe required for rapid growth of the oceanic diatom is substantially lower than values for coastal or estuarine species in this and other studies. Computations concerning the phytoplankton carbon that can result from use of a particular amount of Fe give different results; therefore, the Fe: Cratio for a genetically adapted low-iron oceanic phytoplankton species is used, rather than values for coastal species as were applied in the past.

These pages describe relatively simple and reliable methods for the culture of marine phytoplankton species useful for feeding marine invertebrates. The methods suffice for the most fastidious algae now routinely cultivable, and simplifications indicated for less demanding species are easily made; for example, omission of silicate for plants other than diatoms. Certain modifications of techniques, ancillary methods, and precautions will be treated briefly because questions often arise concerning them, but documentation will be minimal and hopefully restricted to publications readily available.

Effects of differing levels of ultraviolet-B radiation on cell concentrations, maximum specific growth rates, and pigment content of the diatom Thalassiosira pseudonana were investigated. Increased UV-B compared to the base UV-B level (intended to simulate the natural level of UV-B present in the environment) tended to show detrimental effects in all parameters. When compared to our normal culture conditions (UV-B excluded), even the base level of UV-B radiation showed detrimental effects in all parameters except chlorophyll a concentrations, the only tested parameter which increased with the addition of UV-B radiation.

The transport and impact of toxic substances are matters of major concern to management of coastal zones. Man’s love for the coastline and its attendant bays and estuaries ensures that, as population and industrial growth continue, the loading of toxic substances into estuaries and the coastal ocean will continue to increase. It is imperative, therefore, that society address the potential toxic effect of anthropogenic inputs to these areas. However, there are two impediments to successfully addressing these concerns.

UV-B radiation (e.g. 310 nm) penetrates approximately the upper 10% of the coastal marine euphotic zone before it is reduced to 1% of its surface irradiance (Jerlov, 1976). There is good evidence that current levels of solar UV radiation depress near-surface primary production in marine waters (e.g., Steemann Nielsen, 1964; Jitts et al., 1976). Marine animals may tolerate current levels of solar UV-B radiation by means of protective screens, avoidance behavior, and repair processes which reverse much of the potential damage inflicted by the radiation. However, as early as 1925, scientific investigators have documented the damage inflicted on marine animals by exposure to sunlight, especially the UV component of the sunlight (Huntsman, 1925; Klugh, 1929, 1930; Harvey, 1930). Utilizing currently available laboratory and field data the present contribution will review the literature relating to the impact of UV-B radiation upon marine organisms.

At a 1977 meeting at the Bigelow Laboratories, there were two recurrent questions: (1) What is the value of the assimilation number? and (2) Do different values signify changes in the nutrient supply? The answers we would currently give to these questions are (1) there is a range of values determined primarily by the light regime in which the alga has grown, and (2) the assimilation number appears to be insensitive to nutrient stress except perhaps when the stress is very severe. The bases for these answers will be presented.

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).

The soda ocean hypothesis (Kempe & Degens, 1985) suggests an early alkaline ocean of high pH and low calcium and magnesium concentrations. The dissolved carbonates were gradually lost during the Precambrian, leaving the present sodium chloride ocean. The Precambrian paleontological record and the calcium physiology of living cells implicate that the stepwisebuildup of calcium in the ancient ocean was of primary importance for the generation of multicellular life and the onset of biocalcification.

Plants carry on two forms of respiration — mitochondrial or dark respiration and photorespiration. Dark respiration, as the name implies, occurs in the absence of light. It also occurs in the presence of light, although the rate of dark respiration may be different in the light than in the dark. Photorespiration, in contrast, occurs only in the light, as the substrate required for photorespiration is generated in the light and is rapidly depleted in the absence of light. In this paper, these two forms of plant respiration will be discussed, with particular emphasis placed on their rates and their effects on primary productivity in marine algae.