Ulothrix Zonata Research Articles

The rhizoid ofUlothrix zonata (Chlorophyceae)

Ulothrix zonata was studied under natural conditions in situ on slides exposed in a river. On them specimens grow in all stages of development. Older filaments are fixed on the substrate not only by the pointed basal cell but mainly by a branched, horizontally expanded rhizoid produced by this cell. The rhizoid grows in correlation with the growth of the filament as a whole. In addition to the basal cell the following cells of the lower portions of the filament are incapable of division and reproduction. Through these cells the upper fully vital cell grows downwards in older stages.

Algal nitrogen fixation in Californian streams: seasonal cycles

SummaryUsing the acetylene reduction technique, nitrogen fixation was measured in Rocky Creek, a small seasonally dry Californian stream. In the 3 years since 1970 nitrogen fixation varied seasonally and spatially, being highest in the early stages of colony growth in shallow, clear regions where there was little shade. The annual rate of N2‐fixation was similar to that found recently for Arctic tundra, but was greater than rates for Antarctic rivulets and less than rates for temperate rocky shores. A hetero‐cystous Nostoc appeared to be the sole organism responsible for this fixation. Nostoc occurred in variously sized gelatinous clumps on the stable boulders on which the co‐dominant alga, Ulothrix zonata, also grew. Maximum nitrogenase activity yielded 70 nmoles C2H4 mg‐1 drywt day‐1 and 123 nmoles C2H4cm‐2 day‐1. Estimated annual amounts of nitrogen fixed in 1971 ranged from 42 in shade to 360 mg N fixed m‐2y‐1 in the most favourable areas. Nostoc biomass reached 33 g dry wt m‐2 and peeled off each year in June‐July. Because Nostoc was confined to stable rocks the biomass per unit area of the stream as a whole was much less, ranging from 0.054 to 1.26 g dry wt m‐2 in the most favourable site. Nostoc was common throughout the length of Rocky Creek and also plentiful in eight out of ten adjacent streams but not in the main river (Eel River South Fork), probably due to high turbulence and turbidity. N2‐fixation in these streams makes a significant, but probably small contribution to the nitrogen income of the nitrogen‐deficient Eel River system. Nostoc colony establishment appears to be controlled by a combination of reduced turbulence and firmer attachment of the colonies to the substrate. Nostoc colony disappearance in June is probably due to nutrient depletion.

SEASONAL CHANGES IN THE PROXIMATE AND FATTY ACID COMPOSITION OF SOME NATURALLY GROWN FRESHWATER CHLOROPHYTES1

SUMMARYThe protein content of the filamentous Cladophora glomerata (L.) Kz., Ulothrix zonata (Web, & Mohr) Kz. and Spirogyra sp., collected from natural populations for 1 year, averaged 8.0–12.4% of the total dry weight; whereas, the corresponding levels of lipid, cellulose and ash were 11.9–16.1%, 10.0–17.8% and 14.6–24.0%, respectively. Mean values for carbohydrates, estimated by difference, ranged from 32.8 to 56.0%. The colonial Scenedesmus dimorphus (Turp.) Kz. and the unicellular Cosmarium laeve Rab., on the other hand, contained more protein, lipid and carbohydrate (estimated by difference) averaging 13–15.0%, 22.5–25.9% and 415–46.8%, respectively, and less cellulose (7.5–9.8%) and ash (8.2–9.8%). A consistent pattern of seasonal variation in the proximate composition was not normally evident for any species, reflecting the influence of several environmental parameters on the algae. Cladophora contained the greatest amount of phospholipid averaging; 10% by weight of total lipid with the smallest quantity (5%) in Scenedesmus. The predominant phospholipid fatty acid in all species was C18:1 followed by C18:2, C18:3 and C16:1 in Cladophora, Ulothrix and Spirogyra, and C16:1, C18:2 and C16:0 in Scenedesmus and Cosmarium. Oleic (C18:1) and hexadecanoic (C16:1) acids were predominant in the neutral lipids of all the algae, followed by C16:0, C18:2 and C18:3. The concentration of the different fatty acids of each Species varied considerably during the year with the proportion of C16:0 and C16:1, usually rising and that of C18:1 failing during the colder months.

A continuous flow apparatus for the culture of filamentous green algae

An apparatus is described in which filamentous algae can be grown under conditions of continuous flow at river levels of nutrients and be harvested at the end of an experimental period. Details of a trial experiment involving the culture of Ulothrix zonata (Weber et Mohr) Kütz. are given.

Attached Algae on Artificial and Natural Substrates in Lake Winnipeg, Manitoba

The attached algal assemblage on navigational buoys and natural rock substrate in Lake Winnipeg in 1969–70 was examined, in the fall after 145 days growth, as part of an overall limnological survey of this important Canadian Great Lake. Only three phyla were represented: Cyanophyta, Chlorophyta, and Chrysophyta (Bacillariophyceae). Green and blue-green algae were more abundant in the south basin, and diatoms were more common in the more oligotrophic north basin. Ulothrix zonata occurred only on substrates in the north basin, and Cladophora cf. callicoma was found only in the south basin. On both natural and artificial substrates a distinct zonation pattern related to water transparency or available light was prevalent. Preliminary results indicated that light was the most important physical factor affecting growth and specific composition of attached algae on substrates in Lake Winnipeg. Biomass values from all stations (dry weight) ranged from 1.7 to 29.1 mg/cm2; with the greatest values consistently occurring between 10 and 25 cm deep on buoys in the south basin. Diatom density and diatom volume were estimated from buoy samples and varied respectively, within the range 2.00 × 105–6.65 × 106 diatoms/cm2 and 0.32–10.00 mm3/cm2. Though direct evidence is lacking, it appears that nutrients may limit growth of attached algae in the north basin, whereas in the south basin, light is the major limiting factor. The specific composition of the algal assemblages on particular buoys was more related to the physical–chemical features of a major river plume in close proximity to the buoy than to a homogeneous Lake Winnipeg water mass. This factor, together with greater turbidity in the shallower south basin, is largely responsible for the observed heterogeneity among the attached algal assemblages in Lake Winnipeg.