Volume 45, Issue 4

A comparative study of the relative sensitivity to ultraviolet radiation (UVR) among seven marine microalgae from the classes Cyanophyceae ( Synechococcus sp.), Rhodophyceae ( Porphyridium cruentum ), Cryptophyceae ( Rhodomonas salina ), Prymnesiophyceae ( Isochrysis galbana ), Bacillariophyceae ( Chaetoceros sp.), Chlorophyceae ( Dunaliella salina ), and Prasinophyceae ( Tetraselmis suecica ), was carried out. Daily exposure for 4 h over a 4-day period with daily increasing doses of UVR (mainly ultraviolet-B, UV-B) led to a continuous decrease in the effective quantum yield (ϕ PSII ) in Rhodomonas salina , Chaetoceros sp. and Isochrysis galbana . In contrast, Tetraselmis suecica did not show a significant inhibition over the 4-day period of exposure. Synechococcus sp., Dunaliella salina and Porphyridium cruentum were able to restore, at least partially, the values of ϕ PSII during the recovery period (white light only, 20 h), even though a significant decrease in ϕ PSII was also measured in these algae after each exposure. Relative inhibition, defined here as the decrease in ϕ PSII after exposure as compared to the value before exposure and normalised to the latter value (RI = ∆ PSII /ϕ PSII ), was fitted against UV-B irradiance according to an equation of the type y = 1 − (a x) c e −bx , where y is RI, x is the UV-B irradiance (W m −2 ), and a, b and c are constants determined from the fit, using unweighted and weighted irradiances. From the fit, the UV-B irradiance for 50% relative inhibition of ϕ PSII (RI = 0.5, E 50 [W m −2 ]), was calculated for each alga. Rhodomonas salina and Isochrysis galbana exhibited the lowest values of E 50 (0.21 and 0.25, respectively, for unweighted irradiance), being the most sensitive algae to UV-B, while the highest value was calculated for Dunaliella salina (0.47 for unweighted irradiance). The E 50 could not be calculated for Tetraselmis suecica since this alga showed an RI maximum of 0.1, and was therefore considered as a species which was highly tolerant of UV-B. A rise in optical density of each algal cell suspension at 680 and 750 nm, as well as in chlorophyll a content determined from methanolic extracts, was evident over the experimental period in all of the species except for Isochrysis galbana and Rhodomonas salina . In these two algae, in contrast to the other species, there was a notable increase in the carotenoid/chlorophyll a ratio, although this had negligible effects for the protection against deleterious UV-B. The phycobilin/chlorophyll a ratio showed a gradual decrease with time in the three phycobilin-containing algae, but it was particularly evident in R. salina after the third day of exposure.

Species composition and spatial variability inside algal turf communities within territories of the damselfish Stegastes nigricans have been studied in a shallow reef flat environment of the Saint Gilles-La Saline reef complex, at La Réunion Island. The sampling of 50 small portions (2 cm long) of staghorn coral Acropora branches and accurate identification and quantification of algal species under a dissecting microscope provided a list of 19 species. Green algae Enteromorpha clathrata and Cladophora socialis and red algae Anotrichium tenue and Gelidiopsis intricata were the most abundant species in the turfs overgrowing Acropora coral branches. A correspondence analysis applied to the samples revealed three major groups of species characterised by (1) Enteromorpha clathrata , (2) Cladophora socialis , and (3) Gelidiopsis intricata . A gradient has been observed from Enteromorpha clathrata turfs usually occurring at the apical parts of the coral branches, to Gelidiopsis intricata turfs present at the basal parts of the branches. The algal composition of the gut contents of Stegastes nigricans was analysed and compared to the algal composition in the field. The feeding selectivity of the fish was established for several algal species. We suggest that Enteromorpha clathrata -dominated turfs correspond to initial aspects of algal colonisation of recently dead corals, while Gelidiopsis intricata -dominated turfs correspond to mature communities; Cladophora socialis -dominated turfs would correspond to the most intensively grazed turfs.

The ultrastructure of vegetative and reproductive cells in Sporocladopsis novae-zelandiae has been studied for the first time to determine the precise taxonomic position of this genus. Vegetative cells contained one parietal chloroplast with 5–8 ulvophycean-type pyrenoids and transverse cell walls with plasmodesmata. The growth of the transverse walls was centripetal by furrow ingrowth. Ovoid zoosporangia initially had one nucleus and a large basal vacuole. Zoospore release occurred by the apical disintegration of the zoosporangial wall and expansion of an apical mucilage plug. Emptied zoosporangia could be occupied by a series of successive new zoosporangia developed from the same mother cell. Zoospores were bi- or quadriflagellate. The flagellar apparatus showed a 180 ° rotational symmetry and overlapped basal bodies with bilobed terminal caps covering their proximal ends. Our study permits us to conclude that Sporocladopsis is an ulvophycean genus. This conclusion is based on the occurrence of overlapping basal bodies, cytokinesis by infurrowing, and ulvophycean type of pyrenoids. Bilobed terminal caps and zoospore release by apical disintegration of the cell wall (which is accompanied by expansion of a mucilage plug) in Sporocladopsis suggest affinities with the order Ulvales. However, the absence of plasmodesmata and the absence of percurrent proliferation of zoosporangia in all members of the order Ulvales challenge this taxonomical position. The plasmodesmata in Sporocladopsis are similar to those in the Trentepohliales and could suggest a relationship with the latter, but the typical features of the Trentepohliales are absent in Sporocladopsis and this absence does not support an affinity between Sporocladopsis and the Trentepohliales. In conclusion, the fine structural characters of Sporocladospsis are paradoxical and it is therefore difficult to relate this genus to an order within the class Ulvophyceae. Molecular data of the genus, which are not available at present, would be necessary before making a final taxonomic decision concerning its ordinal position inside the class Ulvophyceae.

The water-soluble antithrombotic polysaccharide sulfate fraction designated GI-1 was isolated from the marine red alga Grateloupia indica . It consists mainly of D-galactose (Gal), L-Gal, 3,6-anhydro-D-galactose (D-AnGal) and 3,6-anhydro L-galactose (L-AnGal). On the basis of the results from 13 C NMR and methylation analysis of completely desulfated GI-1, we assigned a typical agarocolloid-carrageenan hybrid type of the backbone consisting of both disaccharide repeating units, [→3)β-D-Gal(1→4)α-D-Gal(1→] and [→3)β-D-Gal(1→4)α-LGal( 1→]. In addition, two repeating units, [→3)β-D-Gal(1→4)α-D-AnGal(1→] and [→3)β-D-Gal(1→4)α-L-AnGal(1→], were also suggested for the native GI-1 from partial methanolysis and 13 C NMR studies.

The chemical composition of the brown alga Padina pavonia (L.) Gaill. from the southern Adriatic Sea was investigated. Twelve sterols were identified in the sterol fraction, the main ones being cholesterol and fucosterol. The main fatty acids in the lipids were also identified. The most abundant fatty acid was palmitic acid, followed by oleic and myristic acids. The concentration of polyunsaturated fatty acids was unusually low for a marine alga. By GC/MS analysis of the volatile and polar fractions, 40 compounds were identified. Some of them probably possess defensive functions. In the volatile fraction free fatty acids, aromatic esters, benzyl alcohol and benzaldehyde predominated. Low concentrations of terpenoids, phenols and sulfur containing compounds were also identified. The n-butanol extract contained mainly fatty acids and polyols. Some of the extracts had an antibacterial activity.

Macroalgae are major components of Atlantic shallow coral reef communities and potentially a major competitor with corals. This study investigates the spatial and seasonal distribution of macroalgal species, which includes fleshy algae, turf algae and some geniculate and non-geniculate corallines, on two inshore and one offshore reef from Porto Seguro Bay, Brazil. Data were collected during the dry season (July/August 1999) and the rainy season (February/March 2000), with samples being taken from the reef slope (at 1, 3 and 5 m depth) and from the reef flat. Macroalgal cover ranged from 33% (reef slope) to 60% (reef flat) on the nearshore reefs, and from 36% (reef slope) to 50% (reef flat) on the offshore reef. The largest number of infrageneric taxa was recorded during the rainy season (February/March 2000), the most abundant genera being Sargassum , Padina , Dictyota , Dictyosphaeria , Caulerpa and Amphiroa . Two species were recorded for the first time in the region: Tricleocarpa cylindrica (Rhodophyta, Galaxauraceae) and Avrainvillea longicaulis (Chlorophyta, Udoteaceae). Algal turf dominated the community structure at all reef sites and habitats. Fleshy algae are the second most conspicuous group on the reef flat in both inshore and offshore reefs. On the reef slopes, corals and zoanthids are second to turf algae in the offshore reef and nearshore reefs respectively.

Growth and toxin production of a noxious phytoflagellate Heterosigma akashiwo (Kagoshima strain) were investigated at a salinity range from 20–40‰. The maximum growth (0.68 ± 0.03 divisions day −1 ) was obtained at 25‰, while the lowest growth (0.48 ± 0.02 divisions day −1 ) was attained at 40‰. The lower salinity was found suitable for maintaining a better morphological condition and motility of the cells. The Kagoshima strain became more toxic at 20‰, and the toxicity decreased with increased salinity. A negative correlation between salinity increase and toxin production was found on HPLC analysis of H. akashiwo toxins (HaTx-I, II, III and IV). Toxin HaTx-IV (corresponding to oxidized PbTx-2) was most dominant and peaked at 20‰ with a yield of 0.3 pg cell −1 . Considerable amounts of HaTx-I and III (corresponding to PbTx-2 and 3) were also detected. However, HaTx-II (corresponding to PbTx-9) was detected only as a trace at 20 and 25‰. A sharp decrease in all toxins was found at salinities above 30‰. The increase of specific growth rate raised the toxin content per cell of the strain.

A twelve-month field survey of the genus Pseudo-nitzschia was carried out in Chinhae Bay, an area of commercial culturing and harvesting of oysters. The study used molecular DNA probes and WGA lectins to determine monthly species abundance and relate this to environmental conditions and nutrients. Ten species of Pseudo-nitzschia were identified during the study: Pseudo-nitzschia multiseries , P. pungens , P. multistriata , P. delicatissima , P. cuspidata , P. subfraudulenta , P. granii , P. fraudulenta , P. subpacifica , and an unidentified Pseudo- nitzschia sp. Of the Pseudo-nitzschia species, Pseudo-nitzschia pungens had the highest cell abundance, followed by P. delicatissima and P. multistriata . The presence of Pseudo-nitzschia multiseries was correlated with domoic acid (DA) contamination of shellfish, for example at Stations (Stn) P2, P3 and P4. Where Pseudo-nitzschia multiseries was recorded, trace levels of DA were detected, but at Stn P1 neither Pseudo-nitzschia multiseries nor DA were detected during the period of this study. Pseudo-nitzschia multiseries is regarded as the most toxic of the DA-producing species known in Korea. Korean isolates of Pseudo-nitzschia multiseries were strongly labeled by WGA lectin and the Pseudo-nitzschia multiseries species-specific DNA probe, and were distributed in seawater of lower temperature (≤ 15 °C) and linked with lower nutrient concentrations, although cell numbers were significantly lower than for Pseudo-nitzschia pungens . The use of the probes puD1, deD1 and frD1 led to the recognition of Pseudo-nitzschia pungens , P. delicatissima and P. fraudulenta , respectively. Although Pseudo-nitzschia species varied depending on month and sampling site, most were present at higher cell densities in lower temperature waters except for Pseudo-nitzschia multistriata . It was demonstrated that these methods provide a simple and rapid technique for the identification of a variety of Pseudo-nitzschia in Korean waters, and offer the opportunity for a series of real-time species detection in the future.

The polysaccharide extracts from Lophurella hookeriana and Lophurella caespitosa together with some derivatives have been examined by 13 C nuclear magnetic resonance spectroscopy and the spectra analysed with the techniques of set theory. The polysaccharides are agaroids that consist of 3-linked D-galactose and 4-linked L-galactose or anhydro-L-galactose. The polysaccharides from both algae were partially sulfated at the 2- and 6-positions of both the 3- and 4-linked units. The polysaccharide from Lophurella hookeriana comprised at least 90% anhydrogalactosyl precursor diads, and was otherwise between 65–75% unsubstituted, with approximately 22% of the 4-linked units being 2-sulfated, 12% of the 3-linked units being 2-sulfated, and 15% of the 3-linked units being 6-sulfated. The polysaccharide from Lophurella caespitosa contained approximately 15% anhydrogalactosyl precursors, 40% L-galactose that was not convertible to anhydrogalactose, and no more than 25% unsubstituted agarose diads following alkali treatment. Approximately 55% of the 4-linked units were 2-sulfated, 28% of the 3-linked units were 2-sulfated, and 25% of the 3-linked units were 6-sulfated.

A total of 15 taxa of marine benthic algae from Guinea-Bissau are identified, namely 3 in the Chlorophyceae, 5 in the Phaeophyceae and 7 in the Rhodophyceae. All of these are new records for Guinea-Bissau.

A diminutive new species of Predaea (Gigartinales, Rhodophyta) is described from coral reef habitats in Puerto Rico,Caribbean Sea. It is composed of compressed lobes which radiate to form an irregularly rounded shape. The new species is characterized by its cylindrical cortical cells, 3-celled carpogonial branches, small number of nutritive cells associated with auxiliary cells and initiation of gonimoblasts from connecting filaments.