Volume 46, Issue 4

A 12-month survey investigated seasonal variations in the vertical distribution of benthic microalgal biomass in relation to major factors potentially controlling their dynamics in the subtropical temporarily-open Mdloti Estuary, KwaZulu-Natal, South Africa. Benthic microalgal chl-a concentrations in the upper 5 cm of sediment ranged from 259 mg m −2 to 977 mg m −2 during the closed phase, and from 6.7 mg m −2 to 305 mg m −2 during the open phase. Significant differences were obtained between sampling sites and among seasons. A distinctive trend of increasing chl-a biomass in the deeper layers of the sediment was noted from the upper reaches (head) to the lower reaches (mouth) of the estuary. Chl-a biomass was virtually homogeneously distributed throughout the upper 5 cm of sediment in the lower reaches. Results suggest that benthic microalgal cells not only exhibited diel rhythms of vertical migration but were actively re-suspended into the water-column of the Mdloti Estuary. While a decrease in salinity, temperature and K d favoured an increase in benthic microalgal chl-a biomass in the upper 5cm sediment, nutrients in the overlying water had no significant impact on the biomass. Results further indicate a physiologically healthy community at all sites during the open phase, as compared to the closed phase of the estuary. During the closed phase, the pheopigment to chl-a ratio indicated an actively growing community in the upper reaches and a “stressed” community in the middle and lower reaches. Thus, the large amounts of “buried” benthic microalgal chl-a biomass found in the upper 5 cm of sediment may represent an important stock of potential primary producers in temporarily-open estuarine systems like the Mdloti.

Thirty-seven different types of dinoflagellate cysts were recorded in surface sediments, sampled at offshore and inshore stations from the southern coastal waters of Korea. Because of their atypical morphologies, Votadinium calvum , Quinquecuspis concretum , Protoperidinium sp. and two types of Brigantedinium are described and discussed in more detail. The concentrations of dinoflagellate cysts were approximately four times higher at offshore stations than those at inshore stations. This study provides a database on dinoflagellate cyst distribution and composition in the southern coastal waters of Korea, where dinoflagellate cysts have been little studied.

Plants of Eucheuma denticulatum collected from Danajon Reef, Bohol, the Philippines were used to produce tissue cultures for the purpose of generating new strains. The plants were sectioned and grown in media encouraging callus growth. New shoots were produced after 3 months of in vitro culture. After another 3 months of laboratory growth, 5 plants were outplanted in the field. After 4 months growth at approximately 0.50 m depth, the five plants grew to biomasses that ranged from 354.9 to 1055.9 g wet weight. They demonstrated growth rates that ranged from 5.8 to 7.2% day −1 . The growth rates of the plants produced through tissue culture in this study suggest that such plants can grow at rates as good as, if not better than, those of ‘seedlings’ produced by the traditional method in the commercial cultivation of E . denticulatum .

The photosynthetic performance of an estuarine population of Ulva rotundata Bliding was determined under natural radiation during a daily cycle. The primary production was estimated following two methods, oxygen evolution and dissolved inorganic carbon (DIC) uptake calculated from the pH change and alkalinity in the media after incubation in closed bottles. Maximum values of oxygen evolution (261 μmol O 2 m −2 min −1 ) were reached during midday. The daily course of the DIC uptake rates was different since the maximum rate (248±10 μmol C m −2 min −1 ) was obtained later in the afternoon. In any case, no photoinhibition was detected by either O 2 evolution or DIC uptake. Additionally, the parameters of photosynthesis vs. photon fluence density curves were similar in spite of the technique used. During the daily cycle, significant changes in CA activity and percentage of photosynthetic inhibition following the addition of an external CA inhibitor (acetazolamide) were produced. However, these changes appeared to have a limited effect on photosynthesis. On the other hand, chlorophyll a and b contents decreased drastically in the afternoon and there was not a good correlation between pigment content and photosynthesis rates. Taken into account the results obtained, the daily primary production of U. rotundata based on oxygen evolution was 20% higher than that based on DIC uptake (1.8 and 1.5 g C m −2 day −1 , respectively).

Dimethylsulfoniopropionate (DMSP) in marine algae has been hypothesized to serve as a compatible solute which functions in osmotic acclimation or cryoprotection. However, many macroalgae that produce large quantities of DMSP live in habitats where they are unlikely to experience large fluctuations in salinities or freezing temperatures. We hypothesized that DMSP has other functions in these algae and that they should not show large changes in DMSP concentrations in response to salinity changes. We tested this hypothesis by placing 1.5 cm 2 diameter disks of the chlorophyte Ulva fenestrata in artificial seawater (ASW) at salinities from 10% ASW to 300% ASW. Over the next 24 h, DMSP concentrations tended to be lower in the algae in the higher salinity media. After 4 weeks, the final DMSP concentrations tended to be highest in the algae grown at the highest salinities, but the mean DMSP concentrations were only 23% higher or 12% lower in algae grown in the high and low salinity media, respectively, relative to algae in 100% ASW. This suggests that osmotic acclimation is not a primary function of DMSP in U. fenestrata . Disks acclimated in 25% ASW, 100% ASW, or 200% ASW then transferred to a higher or lower salinity did not generate measurable amounts of dimethylsulfide (DMS), demonstrating that U. fenestrata is not using DMSP cleavage as a short-term mechanism for reducing internal DMSP stores, as occurs in some phytoplankton. Survival, as measured by the absence of bleaching, was highest in intermediate to high salinities. Growth was highest in low to intermediate salinities and reproduction only occurred in intermediate salinities. These results suggest that U. fenestrata can tolerate salinity changes, but uses metabolites other than DMSP for osmotic acclimation. Based on the results of this and previous studies, we propose that DMSP has other functions in U. fenestrata such as acting as an herbivore deterrent or antioxidant.

A new species of the red algal genus Leveillea , x L . major M.J.Wynne, is described from the Sultanate of Oman, the northern Arabian Sea. This species is distinguished from L . jungermannioides (Hering et Martens) Harvey, a species widely reported from the Indian and tropical western Pacific Oceans, by its larger stature, its erect habit, its bladelets, which are larger, more attenuate, and strongly overlapping, and the absence of tendril formation by the distal portions of axes. Tetrasporangiate thalli are described in the new species, which is known only from the Sultanate of Oman. Leveillea jungermannioides also occurs in Oman, and the two species co-occur in the Al Sharqia region.

A protocol using physical, chemical and enzymatic treatments was developed to prepare cell wall fractions enriched in structural proteins from the red alga Palmaria palmata . The walls obtained from cortical and medullary cells of soft and rigid thalli were chemically characterized. They were all rich in proteins (29–36% DW ) and contained ash (4–34% DW ), xylose (6–19% DW ), glucose (5–13% DW ) and galactose (1% DW ). Fractions from cortical cells were richer in ash, while those from medullary cells were richer in xylose. The amino acid composition of the fractions differed from that of the initial starting algal materials. They were enriched in tyrosine and methionine, which could indicate peculiar protein cross-links such as phenolic couplings and/or disulfur bridges. Extraction of these fractions by 2 M NaCl isolated minor amounts of materials (approximately 10% DW of cell wall fractions) containing glucose, xylose, proteins, galactose and sulfates. The protein-rich insoluble residues were partially degraded by bromelain, papain, trypsin and chymotrypsin into minor amounts of proteic fractions, indicating that the proteases have a restricted access to the cell wall proteins, probably as a result of high proportions of cross-links. Some fragments contained proteins and xylose, galactose and glucose, suggesting the existence of glycoside side-chains on proteins and/or linkages between cell wall polysaccharides and proteins. The difference in the composition and structure of proteins in the cell wall fractions from soft vs. rigid thalli, and from cortical vs. medullary cells demonstrated that these cell wall structures are closely regulated in relation to cell development and specialization.

The structures of the polysaccharides extracted from Griffithsia antarctica and Ceramium uncinatum , both from the family Ceramiaceae (order Ceramiales) were evaluated. Both were based on the agar structure with a high level of precursors. The polysaccharide from Griffithsia antarctica was almost completely sulfated at the 4-position, with approximately half the 4-linked units either anhydrogalactose or its precursor (in about equal amounts comparing the sugar analysis with the linkage analysis), and the other half sulfated at the 3-position and, additionally, with 2-xylosyl, 2-sulfate or 6-sulfate ester as substituents. The polysaccharide from Ceramium uncinatum was somewhat different in nature. One in four of the 3-linked units was sulfated at the 6-position, while half of the 4-linked units were in the anhydrogalactosyl form, with approximately equal amounts of galactose, galactose 6-sulfate (anhydrogalactose precursor) and galactose substituted with xylose making up the remaining 4-linked units. Both polysaccharides showed low levels of 6- O -methylgalactose and 2- O -methyl-3,6-anhydrogalactose.

The structures of polysaccharides from two members of the family Rhodomelaceae have been determined. The polysaccharide from Polysiphonia atterima was very similar to those determined previously from Polysiphonia species, and consisted of substituted agar and precursors, but with the 3-linked units substituted at the 6-position with sulfate ester (60 %), methyl ether (5 %) and low levels of xylose, and 5 % of the 4-linked units being non-sulfated L-galactose. The polysaccharide from Pterosiphonia pennata was a substituted agar with low levels of precursors.Following alkali treatment, the chain comprised only agarobiosyl units, in which 26 % of the 3-linked units were substituted at the 6-position with sulfate ester, and 56 % of the anhydrogalactosyl units were 2- O -methylated.

The polysaccharides from Sarcodia montagneana and from Sarcodia flabellata were examined by 13 C NMR spectroscopy. Analysis of these spectra showed the 3-linked D-galactosyl units were mostly substituted at the 2-position by sulfate ester, and at the 4,6-position by pyruvate acetal. The 4-linked galactosyl units were almost entirely in the L-configuration, the 3-position was almost entirely substituted by sulfate ester, and a high percentage of these were substituted at the 2-position by sulfate ester. However, there was also a significant fraction of the 4-linked units with 2,3,6-trisubstitution by sulfate ester, and these units appeared to be linked to 3-linked units substituted with 2-sulfate ester and pyruvate, that is, these diads had no non-substituted hydroxyl group. A previous report that Sarcodia polysaccharides are equivalent to λ-carrageenan is wrong, but the polysaccharide is similar to the polysaccharides previously isolated from Trematocarpus species, confirming an association suggested previously on the basis of gene sequencing.