Volume 42, Issue 4

Carpospore liberation, germination and carposporeling growth were investigated in Gracilaria cornea J. Agardh at different combinations of temperature and irradiance in laboratory cultures. Maximum number of carpospores released per cystocarp approached 2500 at 25 °C and 10 μmol m −2 s −1 . Student Newman Keuls multiple comparisons showed that the number of carpospores released were significantly different (P < 0.05) between low (10, 25, 50 μmol m −2 s −1 ) and high (75 and 100 μmol m −2 s −1 ) irradiances at 25 °C. The highest carposporeling specific growth rates ranged from 4.6 to 5.2% d −1 , corresponding to a doubling time of 19.2 to 21.7 days and occurred at 25 and 28 °C at the lowest irradiance levels tested (10 and 25 μmol m −2 s −1 ). At 31 °C spore release and sporeling growth were significantly depressed regardless of irradiance. Favourable conditions for carpospore release were found at 25 °C and low irradiances (10, 25 and 50 μmol m −2 s −1 ). The best conditions for sporeling growth in G. cornea were at 25–28 °C and low irradiance. These temperatures corresponded to the environmental conditions during spring on the G. cornea beds from the Yucatan coast.

Three species of Sargassum ( S. carpophyllum , S. ilicifolium and S. siliquosum were collected each month for a period of one year from the inter- and subtidal zones of Pangil, Currimao, Ilocos Norte, The Philippines. Average monthly biomass was species-specific and significantly influenced by the effect of fertility states of the seaweed, collecting zone, and collecting months. A higher biomass of reproductive plants was accounted for in all species in both zones. Among the three species, S. siliquosum had the highest reproductive and vegetative biomass in both zones, followed by S. carpophyllum and S. ilicifolium . Maximum fertility was observed in October for S. carpophyllum and in November for S. ilicifolium and S. siliquosum . Minimum and maximum reproductive biomass was recorded in May and December, respectively in all species. Biomass of vegetative or non-fertile plants was highest in September in all species except for S. carpophyllum , while minimum biomass was recorded in March for S. carpophyllum and May for S. ilicifolium and S. siliquosum . Reproductive plants had more biomass than vegetative plants. The average monthly wet biomass (g m −2 ) of other Sargassum species was higher in the subtidal than in the intertidal zone. The biomass of seaweeds associated with Sargassum did not follow a definite pattern. Although water temperature, pH and salinity values were relatively constant, slight variations of temperature were positively correlated (P = 0.05) with subtidal biomass.

The yield (%) and viscosity (cps) of alginate from Sargassum carpophyllum , S. ilicifolium and S. siliquosum collected along the inter- and subtidal zones of Currimao, Ilocos Norte were determined monthly for a period of one year. Results show that each species demonstrated an individual pattern of alginate characteristics which is significantly influenced by the collecting zone, fertility state, and collecting month (P < 0.05). Positive correlations were observed in alginate yield and viscosity with species and fertility states. Among the three species, S. ilicifolium is the best species for alginate production for the food industry based on viscosity characteristics, followed by S. siliquosum and S. carpophyllum .

On the basis of original plankton and sea-ice samples from the Siberian seas the morphology of the theca in the dinoflagellate Peridiniella catenata has been studied using both light and scanning electron microscopy. All available data on the ecology and geographical distribution of the species have been analysed, its range being presented. It is concluded that P. catenata is one of a few Arctic-boreal dinoflagellates, and cold-water, euryhaline, brackish-water-marine, ice-bound planktonic species. It is the only dinoflagellate hitherto known which is able to develop in abundance in the sea ice. Considering the thecal morphology with emphasis on the sulcal plates, the systematic position of P. catenata , along with the two other species, P. sphaeroidea and P. danica , in the same genus seems to be natural.

A catalogue of the benthic seaweeds from Corrubedo salt-marsh (NW Iberian Peninsula) is presented. In all, 84 species were identified comprising 49 Cyanophyta, 6 Rhodophyta, 10 Heterokontophyta and 19 Chlorophyta. For each species littoral level, substratum, habitat, canopy of vascular plants, and season of collection are reported. Many taxa are of biogeographical interest. Vaucheria arcassonensis , V. intermedia and Wittrockiella paradoxa are new records from the Iberian Peninsula. The Cyanophyta and Chlorophyta constitute 81% of the species reported. Chlorophyte algae together with Vaucheria spp. form the most extensive populations in the salt-marsh.

Padina tetrastromatica Hauck was first reported from Pacific México by Setchell and Gardner nearly seventy years ago, and this record has been repeated by subsequent authors. This taxon was not found, however, either in recent collections or in investigations of herbarium material. Padina tetrastromatica differs from other species of Padina by having fewer rows of cells in the central portion of the thallus. The Setchell and Gardner record of P. tetrastromatica is representative of P. crispata Thivy. Padina tetrastromatica does not occur in Pacific México.

An exceptionally productive flowering season was observed in the Mediterranean meadows of Posidonia oceanica (L.) Delile in the autumn of 1994. At that time some hermaphroditic inflorescences were bagged, and set fruits, indicating that this species can be self-fertile. By spring 1995, the fruits of P. oceanica had matured; the seeds from nine Mediterranean meadows [French continental (3 populations), Corsica (5 populations) and Tunisian coasts (1 population)] were harvested, weighed and analysed for enzyme diversity. Genetic variability was estimated based on the enzymatic polymorphism of 9 loci. Three of the loci were found to be monomorphic, two were frequently polymorphic within only one population and the remaining four were polymorphic in most of the populations. This demonstrated there was very little genetic variability, with an average observed heterozygosity of 0.0205 for all loci within all populations. According to the Hardy-Weinberg equilibrium, expected heterozygosity was 0.0226. The observed lack of heterozygotes was not statistically significant. The enzyme polymorphism of seeds did not show a geographic diversity pattern although the bio-mass of seeds increased along a north-south gradient suggesting an increased reproductive fitness towards the southern Mediterranean populations. These results support the hypothesis that P. oceanica meadows are made up of a few clones extending over large areas. The clonal growth and self-fertilisation in these populations suggest a predominance of autogamy resulting in a high degree of inbreeding.

The Bahía Blanca estuary is a shallow, well mixed and highly turbid ecosystem. The phytoplankton is dominated by diatoms with Thalassiosira the major genus in number of species and numerical abundance. A longterm investigation was conducted from 1978 to 1991 including measurements of phytoplankton composition and abundance and environmental factors. Principal Components Analysis (PCA), applied to two periods of four years (1978–1981 and 1988–1991) corroborated the pattern of seasonal distribution in Bahia Blanca estuary; a winter-early spring bloom as the most important event in the annual cycle. This bloom was initiated usually in late-June and extended through September. Seasonal patterns of nutrient concentrations showed a decline coinciding with the diatom bloom and peaks of high concentrations in late summer and autumn. According to the long term observations on phytoplankton and the PCA results, the most important phytoplankton taxa in Bahía Blanca estuary exhibited one of three types of seasonal patterns: very recurrent, winter-early spring blooming species, which included Thalassiosira curviseriata , T. anguste-lineata , T. pacifica , Chaetoceros spp., Skeletonema costatum ; species present year-round, e. g. non-blooming species Thalassiosira hendeyi and Paralia sulcata ; species with peaks of abundance in late-spring or summer, and presenting more seasonal and interannual variability including phytoflagellates, and the diatoms Cerataulina pelagica and Guinardia delicatula .

A new monostromatic species of Rhipiliopsis , R. papuensis , is described from shaded subtidal habitats on the south coast of Papua New Guinea. Closely related to R. novae-caledoniae Farghaly et Denizot, it differs in having a basally corticated stipe, a lack of wall thickenings above the dichotomies of the blade siphons, and by its very regularly sinuous siphons that are linked laterally by evenly spaced cohesion papillae. New distribution records are made of R. gracilis Kraft, from the same locality as R. papuensis , and of R. echinocaulos (Cribb) Farghaly and R. madagascariensis Farghaly et Denizot from the Seychelles Islands in the western Indian Ocean. A key to the monostromatic species of Rhipiliopsis is presented.

The fatty acid composition of the tropical genus Halimeda (Halimediaceae, Bryopsidales), represented by the six Caribbean species Halimeda opuntia (Linnaeus) Lamouroux, Halimeda goreauii (W. R. Taylor), Halimeda copiosa Goreau et Graham, Halimeda monile (Ellis et Solander) Lamouroux, Halimeda simulans Howe, and Halimeda incrassata (Ellis) Lamouroux, is reported for the first time. The six species possessed similar fatty acid compositions with some exceptions. Principal fatty acids were 14:0, 16:0, 18:2 ( n -6), and 18:3 ( n -3), followed by 20:4 ( n -6), and 20:5 ( n -3). These species contained only 16:3 and no 16:4 as the key C 16 polyunsaturated fatty acid. In the species of Halimeda studied the 18:1 ( n -7) /18:1 ( n -9) ratio was less than 1, with the exception of H. monile where it was close to 1. The very long-chain fatty acids tetracosanoic acid (24:0), pentacosanoic acid (25:0), and hexacosanoic acid (26:0), were identified in H. copiosa , H. monile , and H. incrassata . The ∆5,9 fatty acids 18:2 ( n -9) and 20:2 ( n -11) ( H. monile ) plus 26:2 ( n -17) ( H. copiosa ) were identified in algae for the first time.

Monitoring cruises were carried out on four coastal transects of the southern Adriatic Sea over two years to investigate the effects of the hydrodynamic regime on environmental factors and phytoplankton species composition and succession. The concentration of nutrient salts is usually low except for the winter months. Biomass levels (in terms of chlorophyll a ) proved to be very low, with values ranging between 0.05 and 1.25 μg Chl a L −1 . Phytoplankton densities showed specific oligotrophic water values and varied in a wide range from 9 × 10 3 to 2.9 × 10 6 cells L −1 ; the maximum values were reached in January-February mainly because of a bloom of the diatom Skeletonema costatum . Diatoms were present throughout the year and represented the majority of the population (44.3 %) together with phytoflagellates (39.6 %), while dinoflagellates and coccolithophorids reached, respectively, 10.3% and 5.8 %. During the year, diatoms were dominant with high cell densities in winter time, while phytoflagellates had a larger distribution over time and reached the highest values in spring and summer. Species diversity values were typical of temperate coastal areas (H' = 2.79 ± 0.73). The type of circulation determined the distribution of thermohaline characteristics, abundance and biomass, as well as species composition and succession of phytoplankton in time. However, no great spatial variations were observed.

A light perturbation experiment on sea ice at Cape Evans in 1996 found significant differences in biomass accumulation between ice algal assemblages exposed to additional UVB, UVA and PAR irradiances and those exposed to either control or elevated PAR and UVA without UVB. Sea ice with its snow cover removed (and thus exposed to additional UVB, UVA and PAR) had a 40% lower rate of biomass accumulation than sea ice with its snow cover removed but covered with UVB-absorbing mylar. Chlorophyll-specific production under PAR was up to 0.05 mg C (mg Chl a ) −1 h −1 although it was approximately 0.02 mg C (mg Chl a ) −1 h −1 at ambient under ice irradiances of 2–6 μmol photons m −2 s −1 PAR. UVB irradiation was found to have a greater impact on highly shade-adapted sea ice algal communities beneath thick ice with a thick snow cover than on thinner ice with less snow.

An experiment was performed in a seagrass bed to examine fertilizer efficiency in enhancing porewater nutrient concentration by analysing nutrient concentration at two levels of a slow-release fertilizer addition (3.6 g and 8.4 g) to the sediment in situ . Nutrient concentrations were analysed in porewater samples taken at different times after fertilization. Ammonium porewater concentration was significantly higher in all experimental treatments than in controls even 20 days after fertilization, while phosphate porewater concentration was enhanced only 2 days after fertilization. The nutrient status of Cymodocea nodosa suggested nutrient limitation at the site for the content either in the below ground and above ground tissues compared with the critical ones reported in the literature. Conversely, the results did not indicate nutrient limitation of Caulerpa taxifolia at the site. Phosphate content in the below ground portion of C. taxifolia grown in medium and high fertilization areas was 88% and 11% higher than in control areas, while P content in blades at the highest nutrient addition decreased by 65 %. Below ground biomass of C. taxifolia was related to the enrichment gradient, while above ground biomass was independent of enrichment.