The ecology of Dunaliella salina (Chlorophyceae, Volvocales): Effect of environmental conditions on aplanospore formation

The conditions leading to aplanospore formation in the green halophilic flagellate, Dunaliella salina (Dunal) Teodoresco, were studied using mixed cultures established from field collected samples. Aplanospore formation generally requires reduced salinity, (at salinities > 20% w/v NaCl aplanospores are rarely formed), nitrogen depletion and the presence of sulphate. Cool temperatures and short daylength may also promote spore formation, whereas pH and irradiance have no effect. Aplanospore formation takes place once the culture has reached stationary phase and, in such cultures, up to 36% of the total cells present can be aplanospores, although percentages of spores of less than 5% are most common. The only exceptions to this are high-phosphate cultures where aplanospore formation occurs early in the growth cycle and then ceases. However, not all cultures are competent to form aplanospores, and some mixed or unialgal cultures never formed aplanospores under conditions identical to those where aplanospore formation was observed in others. The factor(s) leading to competency are not known. Unlike free-living cells of D. salina, the aplanospores contain the ketocarotenoid, canthaxanthin

A rapid and inexpensive method for surface sterilisation of Ecklonia radiata (Phaeophyta) for tissue culture

Sections of the thallus of the brown alga Ecklonia radiata (C. Ag.) J. Ag. were surface sterilised for tissue culture by dipping in 70% ethanol for 30 s, followed by sterile deionised water for 30 min. A high percentage of aseptic viable explants could be obtained using this treatment, and growth in vitro was initiated

Growth of microalgae on undiluted anaerobic digestate of piggery effluent with high ammonium concentrations

Anaerobic digestate of piggery effluent (ADPE) is extremely high in ammonia toxic to many microorganisms. Bioprospecting and nutrient enrichment of several freshwater and wastewater samples combined and further acclimation resulted in a mixed culture containing at least three microalgae species capable of growing on undiluted ADPE. Outdoor growth of the mixed culture using raceway ponds showed potential for up to 63.7 ± 12.1 mg N-NH4 + L −1 d −1 ammonium removal from the ADPE. The microalgal consortium was dominated by Chlorella sp. and was stable at between 800 and 1600 mg N-NH4 + L −1. Regulation of CO2 addition to the ponds to maintain a pH of 8 increased chlorophyll content of the microalgal consortium. Average microalgal biomass productivity of 800 mg N-NH4 + L −1 culture conditions during five weeks semicontinuous growth was 18.5 mg ash-free dry weight L −1 d −1. Doubling the ammonium concentration from 800 to 1600 mg N-NH4 + L −1 resulted in a 21% reduction of productivity, however the culture grown at 1600 mg N-NH4 + L −1 with the addition of CO2 by keeping pH at pH = 8 led to a 17% increase in biomass productivity

Tissue culture of brown seaweed

The harvesting of macrophyte algae (seaweeds) is well established and on a world-wide scale more than 180,000 tonnes dry weight of algae such as the phaeophytes Laminaria, Undaria,Sargassum and Macrocystis, the red algae Eucheuma, Gracilaria and Porphyra, and the green algae Ulva, Monostroma and Caulerpa are harvested annually. Much of this algal biomass comes from farmed rather than wild species. The red and brown algae are the source of the phycocolloids agar, alginate, agarose and carrageenan which are of fundamental importance to the development of biotechnology; i.e. for the culture of microorganisms (agar), for the separation of biomolecules (alginate and agarose) and for the production of food products (agar, carrageenan, alginate). The successful large-scale cultivation of these algae requires, amongst other things, the ability to select fast growing and disease resistant strains which produce large quantities of the desired phycocolloid. To this purpose classical plant breeding programs are being carried out, however these are slow and the production of superior cultivars takes much time and effort (Van der Meer 1988). In recent years there has therefore been much interest in developing protoplast and tissue culture systems which would allow more rapid selection and propagation of suitable cell lines, the possibility of producing hybrids by cell fusion and new strains by genetic engineering (Polne-Fuller and Gibor 1987b, Le Gallet al. 1990). Work in our laboratory has concentrated mainly on the brown algal genera Ecklonia and Cystophora. Ecklonia was chosen because it is easily obtained and is a potential source of alginate, and Cystophora, a genus endemic to Australia and New Zealand, because previous studies indicated that this genus appears to be a good source of tocopherols and tocotrienols (Gregson et al. 1977, Kazlauskas et al. 1981, unpubl. results). The tocopherols are of interest and also provide a convenient model for the study of the production of secondary metabolites in algal tissue culture. In this paper we describe some of our findings on the tissue culture of these species and on their tocopherol content

Influence of the shoot density of Halodule wrightii Ascherson from rocky and sandy habitats on associated macroalgal communities

This study evaluated the influence of the shoot density of the shoal grass Halodule wrightii on the composition of the associated algal community, in rocky and sandy habitats on the coast of Ceará in northeastern Brazil. The phycological community included 18 species in 10 families, members of Rodophyta (72.2%), Chlorophyta (22.2%) and Phaeophyceae (5.5%). The largest proportion were epilithic (50%), followed by epiphytes on H. wrightii (38.4%), epipsammics (8%), and epiphytes on other algae (4%). Epiphytes on H. wrightii occurred mainly associated with rhizomes, but also tendrils of H. musciformis occurred attached to the leaves. The phycological community varied according to the density of H. wrightii, independently of particular characters of the meadows, although both habitat and other environmental variables seemed to influence the macroalgae composition and diversity. The rocky habitat was more diverse than the sandy habitat, but in the sandy habitat the shoal grass was important for algal settlement in areas where hard substrates were scarce or absent

Heydrichia homalopasta sp. nov. (Sporolithaceae, Rhodophyta) from Australia

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

Marine benthic flora of the Dampier Archipelago, Western Australia

Two hundred and ten species of marine algae, seagrasses and cyanobacteria are reported from the Dampier Archipelago, northwestern Western Australia. Included are 114 species of Rhodophyta, 50 species of Chlorophyta, 32 species of Phaeophyceae, 5 species of Cyanophyta and 9 species of seagrasses. This report presents the first detailed account of marine benthic algae from tropical Western Australia. Fifty-seven species are newly recorded for Western Australia, with five species (Codium dwarkense, Dictyota friabilis, Balliella subcorticata, Cottoniella amamiensis, Polysiphonia pentamera) also newly recorded for Australia. The algal flora of the region includes many elements common to tropical areas worldwide

Comparison of water velocity profiles through morphologically dissimilar seagrasses measured with a simple and inexpensive current meter

The influence of seagrass morphology on water flow was studied by measuring water velocity profiles through natural seagrass meadows. An array of eight solid-state electronic current meters was used to obtain profiles through meadows of Amphibolis griffithii (Cymodoceaceae), a seagrass which possesses a profusely-branched erect stem with terminal leaf clusters, and two strap-like seagrasses, Posidonia australis and P. sinuosa (Posidoniaceae). Significant differences were observed in the shapes of velocity profiles of the different seagrass species; in particular, a region of high water velocity was observed beneath the leafy canopy of Amphibolis, but not in the Posidonia canopy. There is a strong correlation between the water velocity profile of Amphibolis plants and the distribution of leaf biomass, highlighting the influence of the 'stem-and-leaf cluster' morphology on the velocity profile. The unusual velocity profile of Amphibolis has implications for the ecology of these ecosystems, and sediment stability in particular. The solid-state electronic current meters used in this study were found to be an effective and inexpensive means of measuring water velocity profiles in seagrass canopies

Alternative culture and treatment systems

Shallow, paddle-wheel mixed, raceway-type ponds (high rate oxidation ponds, HROP) are generally used in the treatment of wastewaters with algae. Recently however, several other types of algal culture systems have been developed which have potential application for the tertiary, or higher, treatment of wastewaters. These include hyperconcentrated algal cultures, immobilised cell systems, dialysis cultures, tubular photobioreactors and algal mats. Depending on the particular application of the algae to wastewater treatment and the ultimate use of the algal biomass, these systems may be much better suited than the 'standard' HROP pond system