Volume 42, Issue 6

Species of the diatom genus Thalassiosira are an important component of the marine phytoplankton all over the world, and the Mexican Pacific Ocean planktonic flora is also rich in species of this genus. In this study 37 net plankton samples from the Gulf of Tehuantepec, Mexico were analyzed, yielding 23 taxa of the genus. Most of the species were studied using combined light and electron microscopy. New records for the Mexican Pacific Ocean are Thalassiosira hendeyi , T. intrannula , T. pseudonana , T. tenera and T. visurgis . The species of Thalassiosira recorded here seem to indicate that the Gulf of Tehuantepec represents a subtropical zone at least in one period of the year.

Mycosphaerella eurypotami sp. nov. and Paraphaeosphaeria apicicola sp. nov. are described from senescent leaves of the endemic needlerush, Juncus roemerianus , an estuarine plant of the U. S. east coast and the Gulf of Mexico. Whereas M. eurypotami fruits in the middle and tip of the leaves, P. apicicola appears only in the apices. Both species are exposed to extreme conditions, such as salt spray and rain, freezing in the winter and subtropical summer temperatures, and alternations between wetting and drying. So far, M. eurypotami has been collected in North Carolina and Virginia, and P. apicicola in North Carolina. Mycosphaerella eurypotami is compared with Monascostroma innumerosum and Mycosphaerella juncellina , and P. apicicola with other Paraphaeosphaeria species.

A highly methylated agar was isolated from Gracilaria arcuata which was harvested from Ishigaki Island, Okinawa, Japan. The yield of the agar was 33.2% (w/w dry algae). Gelation occurred at a concentration of 0.35% (w/v) at room temperature. The total carbohydrate, sulphate, ash and methoxyl content were 85.0, 0.8, 3.8 and 13.4% (w/w), respectively. The methylated sugar was identified as 6-O-methyl-D-galactose and 2-O-methyl-anhydro-L-galactose residues, respectively, by 13 C- and 1 H-NMR spectroscopy. The methylated agar was composed of D-galactose, 6-O-methyl-D-galactose, 3,6-anhydro-L-galactose, and 2-O-methyl-3,6-anhydro-L-galactose.

Assays of nitrate reductase activity (NRA), glutamine synthetase activity (GSA), and alkaline phosphatase activity (APA) were used to measure nitrate, ammonium, and phosphate assimilation in five macroalgal species in three estuaries of Waquoit Bay, Massachusetts, U. S. A., subject to different N loading rates. The NRA significantly increased as loading rates of nitrate increased in Cladophora vagabunda and Gracilaria tikvahiae , with C. vagabunda exhibiting the greatest response. The GSA was always higher than the recorded NRA activity, but did not respond to the nitrogen loading gradient in any of the macroalgal species. The APA depended on nitrogen load in Cladophora vagabunda only. The NRA increased as internal nitrogen pools increased in Cladophora vagabunda , Gracilaria tikvahiae , and Fucus vesiculosus . Higher percent tissue N and lower C : N were found in Cladophora vagabunda , Gracilaria tikvahiae , and Fucus vesiculosus in higher N estuaries. Increases in percent tissue N, and increases in NRA, were due to higher loads of nitrate entering the estuary. Increased nitrogen loads correlated to increased C : N in macroalgal tissue, which correlated to increased NRA in Cladophora vagabunda and Gracilaria tikvahiae . This link illustrates that these two opportunistic macroalgal species best access the available inorganic nitrate pool in estuaries subject to eutrophication in Waquoit Bay.

Cultured Grateloupia filicina was used as the material for observations on spore development and the ultrastructure of pit plugs. The general characteristics of the pit plugs were the same in the discs, filaments and frond-like thalli of this red alga. The pit plugs were naked (no cap layers) with a cap membrane and a plug core. The matrix was diffuse in the center and dense in the outer portion. However, the sizes and shapes of the pit plugs varied. Pit plugs of the filament-like medullary cells of the frond-like thalli were the largest. These pit plugs were H-shaped with a deep central constriction. Pit plugs of the filament cells, were bead-shaped and were smaller than those of the medullary ones. In contrast, pit plugs of the cortex of the frond-like thalli were the smallest. The pit plugs of disc cells and terminal ball-like structures on filaments, were a little larger than the cortex and filament cell pit plugs, and were roughly round-shaped, like those of the cortex. This study confirms that the pit plugs of red algal vegetative cells have taxonomic value, even among the same species in different growth phases.

Chaetoceros Ehrenberg, subgenus Hyalochaete Gran, section Compressa contains the species Ch. compressus Lauder 1864 and Ch. contortus Schütt 1895. On the basis of apparent intermediate forms, they were synonymized by Gran and Yendo. Rines and Hargraves suggested that they might be distinct taxa. Light and electron microscopy studies of a wide range of material supports that opinion, although further study of Ch. compressus sensu Lauder from the Indo-West Pacific is needed. Differences of opinion as to whether these taxa should be combined or considered distinct can be attributed to increased knowledge of the biology of diatoms, and advances in systematic theory.

The sequence of intertidal colonization by Sargassum muticum at Aramar Beach (North of Spain) was studied during three years following its first recorded appearance. Only two plants were found in a low-shore intertidal rockpool in the first year. The following year mid-shore and low-shore intertidal rockpools were colonized but only a few plants were attached to low intertidal rocks. During the third year plants covered all available intertidal substrata between 0.0–0.4 m above L.A.T. as well as the related rockpools. Differences in percent cover, size of primary lateral branches, density and reproduction were significant between tidal levels and habitats although mortality of recruits was similar (close to 95% at all tidal levels). The low intertidal, with ample free space available, was the main site of attachment after the first two years of colonization. The seasonal cycle of growth and reproduction showed differences in relation to the tidal level, with a shorter period of growth and reproduction as well as a longer dormancy period at mid-shore rockpools. A conceptual model for the spreading of S. muticum at Aramar is also proposed.

Pico- (0.2–2 μm) and small (2–10 μm) nanophytoplanktonic assemblages were investigated along the Strait of Magellan at the beginning of the austral autumn. Three main areas were identified on the basis of hydrological data: an area characterised by high runoff from fjords, a divergence zone and an inland sea in the shallow eastern part of the channel (Paso Ancho). In the study area picophytoplankton abundance ranged from 8.10 × 10 5 to 3.28 × 10 7 cells L −1 . Cyanobacteria outnumbered picoeukaryotes on average by one order of magnitude; however prokaryotes to picoeukaryotes ratios varied along the Strait. Nanophytoplankton (2.20 × 10 5 to 5.0 9 × 106 cells L −1 ) were mainly represented by cells 2–3 μm (60%, mean value). Picophytoplankton and nanophytoplankton accounted respectively on average for 46% and 27% of the total chlorophyll a which ranged from 0.02 μg L −1 to 1.0 μg L −1 with a mean value of 0.32 μg L −1 . Along the Strait phytoplankton displayed quite uniform size structure. Higher chlorophyll a concentrations were observed in the northernmost part of Paso Ancho where microphytoplankton was dominant, while lower chlorophyll a concentrations and lower prokaryotes: picoeukaryotes ratios (2 to 6) were found in the divergence zone.

A lectin from the alga Codium giraffa , reported as an endemic species of Mexico, was purified by a combination of ammonium sulfate fractionation, affinity and anion exchange chromatographies. Giraffine, as we called this lectin, shares some characteristics with other lectins isolated from the same genus. It is a monomeric protein with a relative molecular weight of 17,800, as shown by native and SDS-PAGE and confirmed by mass spectrometry; its isoelectric point was 6.4 and it did not show multiple molecular forms. The agglutinating activity of this lectin was inhibited with low concentrations of N-acetylglucosamine and N-acetylgalactosamine and was independent of divalent cations.

Using light and electron microscopy, the frustular morphology of two structurally related marine Cocconeis species, C. pseudomarginata Gregory and C. caribensis sp. nov. , is described. Cocconeis pseudomarginata has very dissimilar valves: the sternum-valve bears an externally depressed sternum, a longitudinal thickening, external elongated and internal circular areola openings; the raphe-sternum valve is concave between the apical axis and the valve margin. The type material of C. pseudomarginata and C. vitrea has been studied for comparison. Cocconeis caribensis sp. nov. , an epiphyte on mangrove roots in the Caribbean Sea, is distinguished by strongly concave and convex valves, high stria density (28–34 in 10 μm in the sternum valve), the presence of hyaline submarginal areas between the sternum and the margin in the sternum valve, and the sigmoid sternum and raphe-sternum. The areola structure and the morphology of the valvocopula and the fimbriae of the sternum valve of C. caribensis sp. nov. are similar to those of C. pseudomarginata .

External morphology, anatomy and reproductive structures were studied in the plants of different populations from 700 km of coastline (out of 885 km) of Pakistan. All these populations are treated taxonomically as Cystoseira indica (Thivy et Doshi) Mairh instead of Stokeyia indica Thivy et Doshi, due to the presence of a primary holdfast and production of rhizomatous branches secondarily from the stipe; the dioecious nature of the areal axes; the presence of non-axillary receptacles and the development of vesicles in the ultimate vegetative branchlets. Variations in the Pakistani populations from those of India in height of plants, plasticity of apex to flattening, size and position of vesicles and size of receptacles are discussed.