Volume 44, Issue 3

Phosphoenolpyruvate carboxykinase (PEPCK) is responsible for light-independent carbon fixation (LICF) processes in a wide range of marine algae, however, little is known about the intracellular localization of the enzyme among different algal groups. Antibodies against PEPCK recognized polypeptides in electrophoresed samples of cell-free extracts from only non-green phytoplankton and macrophytic Phaeophyta while antibodies against phosphoenolpyruvate carboxylase (PEPC) recognized polypeptides in samples of only chlorophytes. This supports the hypothesis that PEPCK is the dominant enzyme in LICF processes in chromophytes while PEPC is the enzyme responsible for non-photosynthetic processes in the chlorophytes. The enzyme PEPCK was immuno-localized in the chloroplasts of the diatom Skeletonema costatum and the kelp Laminaria setchellii which differs from the localization of the enzymes in most vascular plants. While LICF processes occur in the cytoplasm of most vascular plants, the results of this study suggest that in marine chromophytes, LICF processes are catalyzed in the chloroplasts and that the flow of carbon varies between these groups of autotrophs.

The importance of thallus fragmentation in the recruitment of the invasive, introduced alga Caulerpa racemosa (Forsskål) J. Agardh at the margins of Posidonia oceanica (L.) Delile beds was studied. A multifactorial experiment was designed to estimate the importance of detachment time on the seasonality of establishment of vegetative fragments and whether this pattern was consistent at different temporal and spatial scales. The approach consists of dispersing drifting fragments of Caulerpa racemosa , detached from substratum 0, 5 and 10 days before, along the margin of a bed of Posidonia oceanica and recording the number of fragments established after 1 month. The results showed that a large number of fragments became established in this habitat and that the greatest number of fragments were found during summer. Surprisingly, the time of detachment from substrate was not found to influence the probability of success in establishment. The results of this study indicated that dispersal by fragmentation is likely to contribute to the wide spread of this alga in the Mediterranean Sea. The spread of this alga via fragmentation is predicted to be the greatest during summer when the largest proportion of fragments are re-established. Geographical patterns of dispersal can thus be interpreted on the basis of this reproductive strategy, of hydrographic studies and experimental evaluation of resistance of fragments to desiccation and drift. The results obtained in this study, together with those obtained at another site using the same experimental approach for Caulerpa taxifolia (Vahl) C. Agardh, suggest that vegetative fragmentation plays a large role in the dispersal of rhizophytic introduced fast-spreading species in the Mediterranean Sea. This reproductive strategy would be in accordance with invasive and fast-spreading abilities exhibited by members of the Bryopsidales.

Ten species of benthic marine algae, new distribution records for the Azores achipelago, are itemised; two other species records ( Heterosiphonia crispella and Laminaria ochroleuca ) are confirmed for the islands. Six species ( Bryopsis pennata , Cottoniella filamentosa , Dasya baillouviana , Feldmannia paradoxa , Heterosiphonia crispella and Lomentaria clavellosa ) show an amphi-Atlantic distribution pattern; four ( Bonnemaisonia asparagoides , Laminaria ochroleuca , Pterosphonia ardreana and Stylonema cornu-cervi ) show a European-African-Mediterranean distribution pattern. The occurrence of Dudresnaya crassa , a western Atlantic warm-water species, represents an extension of its known distributional range to the east. An Ahnfeltiopsis was found which resembled A. intermedia , a species that occurs in the Atlantic Ocean to the south of the Azores.

The effect of nutrient availability on Macrocystis pyrifera recruitment and survival of juvenile sporophytes was examined at its southern limit off Baja California, Mexico. Nitrate levels were inversely correlated with water temperature (r 2 = 0.70) at the experimental location. Low concentrations of nitrate occurred during most of 1998 (< 3 μM) except in spring (4.8–18.8 μM ). Experimental seeding with sporophylls and fertilizing the plants with a slow-release inorganic fertilizer produced successful recruitment when the water temperature was declining (18.7 °C). Survival of transplanted juveniles was significantly higher when fertilized during a period of particularly warm water and low nutrients in 1998 caused by El Niño. Analysis of tissue nitrogen suggests that plants were nutrient-limited during this period, and possibly affected synergistically by temperature stress. The results indicate that nutrients directly affect recruitment and survival of giant kelp at its southern limit, particularly during El Niño conditions.

The allocation of biomass to receptacle, holdfast and vegetative tissues differed significantly between Sargassum elegans and Sargassum incisifolium , two sympatric dominant species of the upper intertidal at Reunion Rocks, KwaZulu-Natal, South Africa. Sargassum elegans , a clumped (many axes per holdfast) species with short primary laterals and a prostrate holdfast allocated a greater proportion of its biomass to the holdfast than did S. incisifolium , an erect species with longer primary laterals, fewer main axes and a conical holdfast. Conversely, S. incisifolium allocated more biomass to the production of receptacle tissue than did S. elegans . These different biomass allocation patterns have previously been considered indicative of different reproductive strategies, i. e. that of sexual reproduction vs. that of persistence and spread in a high wave action environment. At any one time, a low percentage (< 15 %) of the main axes of S. elegans thalli were found to be reproductive, whereas a significantly higher percentage (> 50 %) of main axes of S. incisifolium were found to be reproductive. Per main axis, S. elegans has a greater reproductive effort than S. incisifolium , however at the thallus level, the opposite was observed. It is suggested that the main axes (modules of the genet) of S. elegans function co-operatively to promote sexual reproduction, but minimize any associated costs.

Heydrichia homalopasta sp. nov. is described from the east coast of Australia. The new species lacks the prominent pit plug caps found in the two South African species Heydrichia woelkerlingii Townsend, Keats et Chamberlain and Heydrichia groeneri Keats et Chamberlain. In habit, H. homalopasta grows as a thin crust (to 1 mm thick), similar to H. groeneri , but differing from the massive crusts (to 15 mm thick) found in H. woelkerlingii . The tetrasporangial nemathecia of H. homalopasta are single sporangial complexes whereas those of the South African species are composed of numerous sporangial complexes.

The polysaccharide from Hymenocladia sanguinea and some of its derivatives have been examined by 13 C nuclear magnetic resonance spectroscopy and the spectra analysed with the techniques of set theory. Extracts from a small number of samples from different locations, and from female and tetrasporic stages, were found to have essentially equivalent polysaccharides. The polysaccharide backbone consists mainly of 3-linked D-galactosyl units alternating with 4-linked D-galactosyl, L-galactosyl and 3,6-anhydro-L-galactosyl units in the ratio 0.57 : 0.38 : 0.05. Approximately 25% of the L-galactosyl units contained the 6-sulfate ester, and were converted to 3,6-anhydro-L-galactosyl units on alkaline treatment. No 3,6-anhydro-D-galactosyl units were found, even following alkaline treatment. Almost all the 3-linked units contained 2-sulfate, the 4-linked D-units 3-sulfate and 2,3-disulfate, but the 4-linked L-units were mainly non-sulfated, apart from the anhydroga-lactosyl precursor 6-sulfate.

The polysaccharide extract from Myriogramme denticulata and some of its 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 which consists largely of one diad repeat unit, comprising 3-linked D-galactose-4-sulfate and 4-linked L-galactose-2,3-disulfate. Minor components which occur either as variations in the polymer, or as separate polymers, include an agar, a pyruvylated material, and a galactan with 6-sulfate ester. The alga is a member of the Delesseriaceae, and the limited data available suggests that the 4-linked L-galactose unit may be characteristic of this family.

A transmission electron microscope investigation of the asci and ascospores of Massarina velatospora was undertaken using material collected from Boracay, Philippines. Our collection agrees with the type material although the ascospores were predominantly 1-septate. It was collected on wood of Sonneratia sp. that had been heavily attacked by molluscan borers. The asci are bitunicate with a thick (2–4 μm), fibrillar endoascus and a narrow ectoascus (100–300 nm) that is thickened at the apex with an ocular chamber in mature asci. Ascospore walls comprise a mesosporium, an electron-dense episporium surrounded by an exosporial mucilaginous sheath and bounded by a delimiting membrane that ruptures in water. A comparison of the ultrastructure of M. velatospora and other aquatic Massarina species is made.

Two species of the genus Sphacelaria, S. solitaria and S. recurva sp. nov., from Korea are described. Sphacelaria solitaria, not previously recorded from Korea, is characterized by the occurrence of both symmetrical propagules with two primary arms and asymmetrical propagules with one of the primary arms branched after its second secondary segment to form two secondary arms. Sphacelaria recurva is a new species, based on specimens collected from intertidal habitats on Namhaedo Island, the southern coast of Korea. The plants are erect, tufted, epiphytic on Hizikia fusiformis , and have sparsely branched filaments. Propagules have two short recurved cylindrical arms without further ramifications and a thick stalk tapering to its base. The subapical cells of these propagules are divided unequally to form the two arms. It is suggested that S. recurva can be placed in the section Furcigerae .

Species of ascomycetes are the principal microbial secondary producers in standing-decaying shoots of smooth cordgrass ( Spartina alterniflora ), the foremost and highly productive grass of saltmarshes of the eastern USA. Rates of expulsion of ascospores from wet, standing-decaying leaves of S. alterniflora were measured in spore-capture chambers seasonally, over a 3-year period. Extents of occupation of decaying leaves were determined by measuring sizes of characteristic patches associated with different species or species groups. Patches of leaf blades not occupied by at least one of the ascomycetes of the smooth-cordgrass ascomycete community occupied less than 0.2% of leaf abaxial area. Patches of the ‘black-peppered’ appearance (containing ascomata of one or more of the following: Phaeosphaeria spartinicola , Mycosphaerella sp. 2, Phaeosphaeria halima ) occupied 91 to 98% of abaxial leaf area for mid-shoot blades at subsites containing tall and intermediate-height shoots. At short-shoot sites, ‘peppered’ patches occupied 53% of leaf area, due to higher levels of periwinkle grazing at short-shoot sites; size of ‘peppered’ patches was negatively correlated with extent of severe invertebrate grazing of leaves ( r = −0.87). Blackened patches (containing ascomata of Buergenerula spartinae ) had an overall average occupation percentage of 17% of leaf area, and the percentage was not significantly affected by periwinkle grazing ( r = −0.13). Attached decaying leaf blades low on shoots and leaf sheaths expelled few spores (< 30% of the average for mid-shoot and upper-shoot blades), and for sheaths, B. spartinae was apparently the principal ascomycete releasing spores. For mid-shoot and uppershoot decaying blades, mean total ascospore-expulsion rate ranged from 14 to 131 spores mm −2 leaf abaxial surface (72 h) −1 , depending on marsh watershed and season. Higher percentages of expelled ascospores for Phaeosphaeria spartinicola were found for autumn and winter (52 to 62% of spores), but for Mycosphaerella sp. 2, peak seasons were summer and spring (42 to 54% of spores). Percentages of ascospores for these two species were uniform over years, marsh watersheds, and tall-to short-shoot marsh subsites, whereas Phaeosphaeria halima exhibited a high degree of spatiotemporal patchiness. Because the ascospore-capture method used does not measure total ascospore release, only minimum values could be calculated for ascospore output m −2 marsh. Calculated minimum rates of total ascospore expulsion for mid-shoot plus upper-shoot blades were 1.3 million spores m −2 marsh h −1 of blade wetness, 5.9 billion spores m −2 marsh yr −1 , and 7.5 g organic mass m −2 yr −1 , amounting to 4.5% of total annual fungal production within these blades.

The lipid and fatty acid compositions of the marine diatom Chaetoceros salsugineus were investigated during the life cycle, including the vegetative and resting stages. The relative proportion of the lipid classes and their fatty acid composition varied during the life cycle. The amount of polar lipids, structural components of the cell membranes, increased rapidly in the period of the resting cell formation. Individual lipid classes were found to have a characteristic fatty acid composition. Changes in the proportion of polar lipids contributed to a difference in the total fatty acids. In polar lipids, polyunsaturated fatty acids, predominantly 16:3(n-4) and 20:5(n-3), composed up to 59% of the total fatty acids, peaking during resting cell formation. The results suggest that in resting cells the structural components of photosynthetic and cellular membranes accumulate, thus ensuring the immediate growth and development of cells upon the return of favourable environmental conditions.

Saldanha Bay and Langebaan Lagoon form together one of the few sheltered habitats within the Benguela Marine Province; a wide gradient in environmental factors is found here. The West Coast National Park was established to protect this unique ecosystem, but at the same time an industrially expanding harbour marks this area. In an effort to understand the biological composition of the Saldanha/Langebaan ecosystem, the intertidal macroalgal assemblages were studied in relation to the relatively well-known South African West Coast flora. Three distinct floral entities were identified using various analytical techniques (similarity coefficients, CCA and TWINSPAN): (i) the species poor, though distinct, salt marshes; (ii) the Lagoon sites; and (iii) the Bay and West Coast sites. The transition between the latter two is located at the mouth of the Lagoon. The species richness of the Bay/West Coast entity is larger than in the Lagoon. The change in algal composition can be explained in terms of the environmental variables of which wave exposure is the most significant. Other important environmental parameters are water surface temperature and salinity, which were found to be negatively correlated with wave exposure. Biogeographical affinities of the different algal entities of the Bay/Lagoon system were also determined in relation to the entire South African shoreline. The Bay/West Coast entity supports a typical West Coast flora, with some noticeable effects of uplift of subtidal species into the infralittoral fringe and morphological variation in less exposed areas. The algal flora of the Lagoon is also dominated by West Coast species, but is typified by species characteristic of sheltered habitats, and with a number of species which otherwise only occur on the geographically distant South Coast (east of Cape Agulhas). The algae from the salt marshes occur widely in tropical mangroves and warm temperate salt marshes.