Volume 42, Issue 5

Iron, Pb, Mn, Zn, Cu, Co, Ni, Cr, Cd, Na, K, Ca and Mg concentrations were determined in leaves, stems and roots/rhizoids of Cymodocea nodosa , in seawater and in sediment from monthly collections from the Thermaikos Gulf (Greece). Statistical analysis demonstrated that only Pb concentrations in the leaves and Co concentrations in the stems displayed significant seasonal variation. However, the variations of Cu, K and Na in the roots/rhizoids between the three seasons (spring, summer, autumn) were also significant. The concentrations of Pb in the leaves and Cu in the roots/rhizoids could, generally, be included in one group of seasonal variation with high values in winter and autumn and low in summer or spring, whereas Co in the stems and Na and K concentrations in roots/rhizoids followed the opposite pattern. The variation of the first group was discussed in relation to the growth dynamics of the plant and of the second seasonal variation with tissue age and with the role of metals in physiological processes. The iron and Mn content in the leaves and Cu in the roots/rhizoids of C. nodosa were negatively correlated with their total concentrations in the sediment and Ca dissolved in the seawater was correlated with the concentrations in the stems. The concentrations of Pb, Cu, Cd and Na in the leaves were correlated with those in the stems; Pb, Cu and Ni concentrations in the stems were correlated with those in roots/rhizoids and Pb in the leaves with those in roots/rhizoids. Leaves of C. nodosa had higher Zn, Cu, Cd, Mn, Ni, Co, K and Ca concentrations than in the stems, whereas roots/rhizoids had higher values of Cu, Cd, Fe, Ni, Co, Cr and K in comparison with stems. The Co and Zn content in the leaves was higher than in roots/rhizoids. Cymodocea nodosa in Thermaikos Gulf could be regarded as a bioindicator for Mn and Cu. Leaves seem to constitute a better bioindicator for Mn, while the best collection time for the plant to be used as a bioindicator for those metals is autumn.

The polysaccharide extracted from Plocamium costatum has been examined by chemical and spectroscopic techniques. Glycosyl linkage analysis of the native polysaccharide revealed a complex sulfated galactan, but the substitution and linkage pattern was not obvious, partly because the 4-linked units are nearly all 3-sulfated and a high proportion of the 3-linked units are 4-sulfated. Glycosyl linkage and 13 C NMR spectroscopic analysis of a solvolytically desulfated sample, however, confirmed a backbone structure of alternating 3-linked β-D-galactopyranosyl and 4-linked α-galactopyranosyl units as expected for a red algal galactan. The 4-linked galactosyl units, however, are present in both the D- and L-configuration in approximately equal amounts.

Photosynthetic activity of the recently-discovered red seaweed Grateloupia doryphora was investigated from oxygen measurements on samples collected in two areas of Brittany (France). Some photosynthetic parameters [maximum photosynthesis (Pmax) and dark respiration (R d )] were studied after short-term incubation at different temperatures and salinities. The results showed that the maximum photosynthetic rate and dark respiration were both increased with temperature elevation. Whatever the seawater temperature, G. doryphora withstood a large range of salinity. Similar results obtained in photosynthetic measurements observed for both populations suggest that they respond to environmental conditions in the same way.

Several studies, mainly in temperate regions, have shown that the polyphenols of brown seaweeds (Phaeophyceae) are responsible for chemical defense against herbivores. In the present work, we tested the susceptibility of 4 species of tropical seaweeds from Búzios, Southern Brazil to herbivory by the amphipod Parhyale hawaiensis Dana, and also analysed the effect of different concentrations of polyphenols from Sargassum furcatum Kützing as a defense against this amphipod. Sargassum furcatum exhibited low levels of polyphenols, consistent with previous observations from other tropical regions, and the natural levels of phenols found in this alga did not inhibited herbivory by Parhyale hawaiensis . On the other hand, high levels of the polyphenols extracted from Sargassum furcatum and the phloroglucinol monomer of the polyphenols inhibited this amphipod. The results obtained reveal that phenolic compounds could be used as an effective defense, but for unknown reasons they are not produced in high quantities by southern Brazilian brown seaweeds, as they are in other regions of the Pacific Ocean.

The following five species of marine red algae are reported from Malaysia for the first time and their characteristic features are described: Cryptonemia yendoi Weber-van Bosse (Halymeniaceae, Cryptonemiales), Caulacanthus ustulatus (Turner) Kützing (Caulacanthaceae, Gigartinales), Chondracanthus intermedius (Suringar) Hommersand (Gigartinaceae, Gigartinales), Griffithsia schousboei Montagne (Ceramiaceae, Ceramiales) and Laurencia flexilis Setchell (Rhodomelaceae, Ceramiales). The presence of Anotrichium tenue (C. Agardh) Nägeli (Ceramiaceae, Ceramiales) in Malaysia is confirmed. Chondracanthus okamurae Abbott, originally described from Japan, is reduced to the synonymy of C. intermedius .

Biogenic agents were isolated from the benthic cyanobacteria Scytonema hofmanni and Calothrix brevissima by various extraction and purification (thin layer chromatography) (TLC) methods. These bioactive compounds were tested on the growth of a benthic diatom. Diatoms present the principal share of biomass of microfouling organisms. Nitzschia pusilla was chosen as the test organism. Extracts obtained from both cyanobacteria species cause strong growth inhibitory effects, Scytonema hofmanni producing the most effective antialgal compounds. The algicides from Scytonema hofmanni are synthesized and localized mainly in the cells, only traces are exuded into the culture filtrates. Antialgal compounds were not detected in culture filtrates of Calothrix brevissima .

The Comacchio lagoonal system has been affected for years by a persistent phytoplanktonic bloom which makes the waters greenish. Surveys carried out from April 1995 to February 1996 showed that this bloom was caused by a Synechococcus sp. and by an Eustigmatophycean belonging to the genus Nannochloropsis . However, while the Synechococcus sp. was mainly present in the summer, Nannochloropsis was always present with constant density values. Moreover, this species shows many ultrastructural features and a pigment composition similar to those of Nannochloropsis spp. and reproduces by autospores. The 18S rRNA gene sequence of this strain is identical to those of five strains of Nannochloropsis gaditana . In this paper, besides phytoplankton (including picophytoplankton), we also report the data of the main chemico-physical parameters. Among them, the salinity and nutrient values showed an anomalous seasonal trend.

The life history, reproduction and impact of fertilization on growth rate of Gracilaria domingensis (Kützing) Sonder ex Dickie were studied in vitro . The life history is of the Polysiphonia -type, and was completed in six months. Carpospores developed into plants which produced tetraspores in 60 days. The gametophytes originated from the released tetraspores became fertile after 101 days with a sex ratio of 1:1. Spermatangia were found in single deep conceptacles, verrucosa -type, as well as confluent ones, henriquesiana -type. Mature cystocarps have a conspicuous fusion cell and tubular nutritive cells formed from the gonimoblast to both pericarp and cystocarps floor. Non-fertilized female gametophytes showed a higher number of new apices during cultivation. Fertilized female branches grew similarly to the unfertilized branches during the first three weeks, but much slower from that time on. The reproductive cost, expressed as growth differential was around 55% smaller than the control.