The Fatty Acid Composition Characteristic of a Highly Migratory Fish,with Seasonal Variation of Docosahexaenoic Acid Content in Lipid of Bonito (Euthynnus pelamis)

Present address: Hagoromo Foods Corporation. 151, Shimazaki-cho, Shimizu-shi, Shizuoka 424-85. Japan.

The seasonal variation offatty acid composition in lipids of various organs and stomach contents of bonito (Euthynnus pelamis) was investigated. Although docosahexaenoic acid in the lipids of the stomach contents originating from their prey organisms varied from about 13% to 31%, it was the dominant unsaturated fatty acid and

accounted for more than 25% of the total fatty acids in the lipids of every organ of bonito in and out of season, and its seasonal variation was comparatively small.     

Non-photosynthetic enhancement of growth by high CO2 level in the nitrophilic seaweed Ulva rigida C. Agardh (Chlorophyta)

The effects of increased CO₂ levels (10,000 μl l⁻¹) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO₂ enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO₂, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO₂ levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO₂ levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO₂ was entirely dependent on the enhancement effect of CO₂ on N-assimilation rates. The increase in nitrate reductase activity at high CO₂ was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO₂ in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO₂ levels is discussed. Received: 27 March 2000 / Accepted: 9 October 2000     

SEASONAL VARIATION OF PHOTOSYNTHETIC PERFORMANCE AND LIGHT ATTENUATION IN ULVA CANOPIES FROM PALMONES RIVER ESTUARY1

The primary production of Ulva populations relies on their photosynthetic performance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic performance of two different species (Ulva rotundata Blid., Ulva curvata (Kütz.) De Toni) blooming in the Palmones river estuary. Light within canopies differed from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. In addition, light was spectrally filtered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are frequently found covering the intertidal mudflats, and therefore, thalli within these mats may be subjected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspecific differences were observed for light-saturated photosynthetic rates (P_max) and light compensation points (L_CP), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima were recorded in winter for P_max, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (R_d) was not seasonally affected, and a maximum L_CP was found in summer. To extrapolate these data to field situations, the temperature dependence of photosynthesis should be considered. The Q₁₀ values were 2.44 for R_d and 1.79 for P_max, whereas the photosynthesis rate at subsaturating light levels was unaffected. The Q₁₀ values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal differences on P_max were damped.     

Topographic cues guide the attachment of diatom cells and algal zoospores

Surface topography plays a key role in the colonization of substrata by the colonizing stages of marine fouling organisms. For the innovation of marine antifouling coatings, it is essential to understand how topographic cues affect the settlement of these organisms. In this study, tapered, spiked microstructures and discrete honeycombs of varying feature dimensions were designed and fabricated in order to examine the influence of topography on the attachment of zoospores of the green macroalga Ulva linza and cells of the diatom (microalga) Navicula incerta. Contrasting results were obtained with these two species of algae. Indeed, the preferred location of cells of N. incerta was dominated by attachment point theory, which suggested a positive correlation between the density of cells adhering and the amount of available attachment points, while the settlement of spores of U. linza was mainly regulated by both Wenzel roughness and local binding geometry.     

BACTERIA THAT INDUCE MORPHOGENESIS IN ULVA PERTUSA (CHLOROPHYTA) GROWN UNDER AXENIC CONDITIONS1

Marine foliaceous green macroalgae such as Ulva lose their typical morphology when cultured aseptically in defined synthetic media. However, after reinfection by certain marine bacteria (isolated from unialgal cultures of Ulva pertusa Kjellman), the organisms regain their typical foliaceous or tubular morphology. To investigate the morphogenesis (MG) induced in U. pertusa by bacteria, we isolated and identified bacteria with MG activity on U. pertusa and studied the distribution of such bacteria in seawater and on various marine macroalgae. We isolated 1555 bacterial strains from 18 species of marine macroalgae (six Chlorophyta, five Phaeophyta, and seven Rhodophyta), from seawater and from sediment collected at the beach at Omaezaki, Shizuoka Prefecture; Japan. Of these, 676 bacterial strains (43.5%) showed MG activity. They were classified into six bacterial groups, Flavobacterium, Vibrio, Pseudomonas, Deleya, Escherichia, and gram-positive cocci. These bacteria were ubiquitous among the samples and were not specific to U. pertusa. Several plant growth regulators had no MG activity. Filter-sterilized supernatants of culture media of MG-active bacteria strains did not induce MG. Cocultivation of Ulva with active bacterial strains is so far the only way to induce the MG effect, which suggests that for MG direct contact between Ulva and the bacterial strain is necessary.     

EFFECT OF CURRENT VELOCITY ON THE DETACHMENT OF THALLI OF ULVA LACTUCA (CHLOROPHYTA) IN A NEW ZEALAND ESTUARY

Experiments were undertaken in a recirculating flume to determine the relationships among water velocity, thallus area, drag, and the probability of thallus breakage or detachment in the foliose green alga Ulva lactuca L. In all specimens tested to breaking point, thalli detached from their bivalve substrates as a result of stipe breakage rather than in midthallus or by holdfast detachment. There was no relationship between thallus size and drag at which detachment occurred. Rather, the probability of detachment was normally distributed about a mean drag of 0. 70 N (95% confidence limits 0.55–0.85 N). Average breaking stress of stipes was 345 kN.m^-2 (95% cl 250–485 kN.m^-2). Similar results were obtained in field experiments where the horizontal force required to detach thalli was measured directly as 0.93 N (95% cl 0.69–1.15 N). Drag coefficients of plants were not constant with water velocity but increased up to 0.4 m.s^-1, declining exponentially at velocities above this. Empirical relationships were established between coefficient of drag and Reynold's number and, hence, among drag, thallus area and water velocity. These relationships permitted estimation of mean water velocity at which plants of a given area would detach .     

THE EFFECT OF A HORN SNAIL ON ULVA EXPANSA (CHLOROPHYTA): CONSUMER OR FACILITATOR OF GROWTH?1

To determine whether California horn snails are more likely to be consumers or facilitators of Ulva expansa (Setch) S. & G. growth in estuaries, we conducted manipulative experiments that evaluated algal growth and the movement of N between the water column, algal tissue, and, in the second experiment, sediments. Algae grew poorly in the absence of sediments, drawing on their own sequestered N supplies (3.5% of dry weight reduced to <2%) and N released by snails and by depleting inorganic N in the water column. There was no evidence of consumption when snail densities ranged from 0 to 900.m^?2 (0, 3, 6, and 9 per aquarium), as algal growth was similar for all snail densities, and snail lengths did not increase during the 21–d experiment. when sediment was provided, N was depleted in the sediment and enhanced in the algal tissue. As in the first experiment, the water column was depleted of inorganic N and enriched with organic N, mostly in the dissolved form. Because both snails and macroalgae often dominate the shallow waters of southern California's lagoons and estuaries, our evidence that the snails are primarily facilitators of algal growth (via transfer of N from sediments to the water column) suggests that snails may play an important role in both food web and N dynamics.     

Metabolism-independent binding of toxic metals by Ulva lactuca: cadmium binds to oxygen-containing groups, as determined by NMR

The metabolism-independent metal binding characteristics of Ulva lactuca were investigated using both freeze-dried thalli and cell walls stripped of intracellular material by incubation in Triton-X followed by methanol. Biosorption of Cd, Zn, Cu and Co by freeze-dried thallus was concentration-dependent and followed Freundlich and Langmuir isotherms. The Freundlich plot suggested that freeze-dried U. lactuca had the greatest binding affinity for Cu compared with Cd, Zn and Co. The BET (Brunauer–Emmett–Teller) plot, which indicates a more complex form of adsorption, and the Scatchard plot were not adequate models for Cu adsorption. The Scatchard plot of Cd suggested that two Cd binding sites were available on the freeze-dried thallus, with the second, lower affinity site only becoming available at Cd loading capacities greater than 4.9mmol g dry wt. Cd nuclear magnetic resonance (NMR) studies confirmed that two binding sites were available for Cd on the freeze-dried algal powder, though only one was available on the cell wall, and that the affinity of the binding sites was greater for Cu than for Cd. The results of the NMR experiments suggested that Cd binds to oxygen-containing functional groups in the algal powder and on the cell wall. It is proposed that sulphate or hydroxyl groups attached to polysaccharide subunits are possible sites.     

TEMPORAL AMMONIUM PATCHINESS AND GROWTH RATE IN CODIUM AND ULVA (ULVOPHYCEAE)1

The growth rates of two chlorophyte macroalgae, Codium fragile and Ulva curvata, are compared in response to varied, but non-random, NH₄⁺ enrichments (pulses). The species were chosen to contrast radically different morphologies. Pulse frequency and pulse duration were varied independently; however, an equivalent mass of NH₄⁺ was added in each treatment. The growth rate of Codium varied neither as a function of pulse frequency nor duration; the growth rate of Ulva varied with pulse frequency, but not pulse duration. These data are combined with life form and physiological characters, and are discussed in the context of the “function form” hypothesis. From the evidence we argue that by virtue of its life form, Ulva is capable of utilizing transiently high NH₄⁺ concentrations and is capable of high growth rates, attributes contributing to its role as a ruderal species. In contrast, Codium's life form does not allow utilization of transiently high NH₄⁺ concentrations or high growth rates, thereby contributing to its role as a persistent species.     

COMPARATIVE CYTOLOGY AND TAXONOMY OF THE ULVAPHYCEAE. I. THE ZOOSPORE OF ULOTHRIX ZONATA (CHLOROPHYTA)1

This fine structural study of the quadriflagellate zoospore of Ulothrix zonata (Weber & Mohr) Kützing, with special attention to the flagellar root system, demonstrates that it is very similar to the zoospore of Ulva lactuca L. in several aspects. Common features include the presence of a cruciate root system (4-2-4-2 type), a non-striated band that connects basal bodies, a so-called terminal cap, and system I and system II striated root components. Only slight differences exist, i.e. in the shape of the terminal cap, and in the number and position of the system II root components. It is concluded that the taxonomic affinities of U. zonata lie with the Ulvaphyceae sensu Stewart and Mattox rather than with the Chlorophyceae. Additional support for this conclusion is the discovery of tiny, flat body scales on the zoospore of U. zonata. A summary of the distinctive characteristics of the Chlorophyceae, Charophyceae and Ulvaphyceae reflecting the current state of knowledge is given.